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Musings of an Energy Nerd

Insulating Old Brick Buildings

If you’re thinking of insulating the interior of a load-bearing brick wall, proceed with caution

Image 1 of 3
Wet bricks can be damaged by repeated cycles of freezing and thawing. The saturated bricks on this old building were unable to handle the stresses created by repeated freeze/thaw cycles. If a brick building is insulated on the interior, the bricks will be colder and wetter in winter, and therefore more vulnerable to freeze/thaw damage.
Image Credit: John Straube

UPDATED March 19, 2013

Older buildings with load-bearing brick walls are common in many northern U.S. cities. While these thick (muti-wythe) brick walls were often plastered on the interior, they were rarely insulated.

Load-bearing brick walls are tricky to insulate. Here’s why: if you insulate the wall on the interior, you’ll make the bricks colder during the winter. As we know from the psychrometric chart, cold bricks are always wetter than warm bricks. Once the wall is insulated, the escaping heat that formerly passed through the bricks is no longer available to drive out the moisture. So your wet bricks stay wet for a long time. In some cases, repeated cycles of freezing and thawing can permanently damage the bricks, causing them to fall apart.

After I began researching and writing this article, I received an invitation to attend the Department of Energy’s Expert Meeting on Interior Insulation Retrofit of Mass Masonry Wall Assemblies, held on July 30, 2011 in Westford, Mass. (The meeting was sponsored by the Building America program.) The presenters at that meeting — John Straube, Henri Fennel, Terry Brennan, Bill Rose, Mark Bomberg, Christopher Schumacher, and Kohta Ueno — all contributed valuable information that helped with this article.

It’s possible to insulate a brick building on the interior

If insulating a brick wall on the interior can make the wall vulnerable to freeze/thaw damage, does that mean such walls should never be insulated? No. But builders who want to insulate an old brick wall should proceed cautiously.

There are no simple rules of thumb when it comes to assessing the vulnerability of an existing brick building to freeze/thaw damage. However, here are the most important points to remember:

  • Most, but not all, existing brick buildings can be safely insulated on the interior.
  • The colder the climate, the greater the risk of freeze/thaw damage.
  • The thicker the insulation, the greater the risk of freeze/thaw damage.
  • The more rain that falls on the wall, the greater the risk of freeze/thaw damage.
  • Some bricks are more vulnerable to freeze/thaw damage than others; there are tests to determine whether your building has good bricks or bad bricks.
  • If you insulate the interior of a brick building, the ends of joists and beams that are embedded in the exterior walls can rot.
  • The first step in assessing the vulnerability of any brick building to freeze/thaw damage is a site visit by a smart observer.
  • If all of this sounds complicated and confusing, you may want to hire a consultant to help you determine the best way to proceed.

The best strategy is to insulate on the exterior

There is a simple way to avoid all of the problems listed above: just insulate your brick building on the exterior. (For more information on this option, see .)

One exterior-insulation approach involves covering brick walls with EIFS — that is, a layer of rigid foam covered with synthetic stucco.

“Exterior retrofit is the preferred building science solution,” says John Straube, a principal at Building Science Corporation in Somerville, Massachusetts. “It’s a great solution for ugly buildings.”

Of course, most owners of historic brick buildings are reluctant to cover up their bricks. As Terry Brennan, the president of Camroden Associates in Westmoreland, New York, explains, “If you can’t do the smart thing — insulate on the outside — then you have to do other smart things to enable you to do the silly thing — that is, to make insulating on the inside work.”

Hiring a consultant

Because of all the uncertainties associated with insulating brick walls, many building owners hire a consultant to advise them. Rather than trusting your neighborhood architect, it’s best to invest in a consultant who specializes in such projects. “The most important thing and the cheapest thing an owner can do is to get Building Science Corporation to send one of our guys to the job site to look at the building,” says Straube.

According to Brennan, “It’s definitely worth hiring an expert, but remember: the experts are still learning.”

Inspecting the building

Don’t assume that the first step in this process is getting your bricks tested. Using a sharp set of eyes, the first step is to inspect the building. “Walk around and look,” says Straube. “Look for stains and rot. Talk to people who have been in the building. Ask them if it has been leaking.”

A humble inspector will speak little and listen much. “The site visit is the most important thing we can do,” says Straube. “Walk around the exterior and interior. The information you gather is invaluable. Look for wetting patterns, signs of erosion. Look where dust is accumulating. Look for rain leaks. Open up walls and look inside of them. Put a hole in the wall — bash some holes in the wall with a hammer. Look at the bricks at grade. Look below windows. Look for freeze/thaw damage. Look at unused chimneys. If the parapet is in good shape, that’s a good sign.”

Since the bricks in unused chimneys and parapets don’t benefit from the heat that usually flows through walls, they act as tell-tales. “You walk around the building, and you notice there is an unused chimney integrated into the exterior wall,” says Straube. “So you ask, ‘How many years has the chimney been not been in use? Oh — twenty years?’ These are bricks in the most exposed part of the building, with no heat flowing through. That’s what I call a full-scale test. Maybe it turns out that this brick in this situation is quite tolerant. If you have tall parapets, they get twice as much rain and no heat flowing from the inside — especially if the parapet is tall. The taller it is, the less heat it sees. In other cases, you might have a building that has been left abandoned, or kept at 40 degrees.” In all of these cases, the bricks have been cold and exposed to freezing weather for years. If they are in good shape, you will probably be able to insulate the building.

“If there are splotches on the bricks away from concentrating rainwater, if you see flaking, then you can tell that the brick is already failing, and you are on the edge,” Straube continued. “Or perhaps you are looking at an in-between case — a building with no parapets or chimneys, where maybe you see some damage at the window corners, some signs of drooling. Maybe there is some metal flashing on the window sills from the last time the windows were replaced, and all the flashing does is direct water to the ends where it dribbles on the walls. Then maybe you see freeze/thaw damage. So now the question is, ‘Can we design water-shedding details that help us step back from the edge?’”

Terry Brennan described a building in Utica, New York, that had problems after it was insulated. “It showed signs of failure after 3 or 4 inches of foam was sprayed on the inside of the 3-wythe brick wall,” Brennan told me. “The building had a bunch of stupid detailing: some projections like gargoyles, as well as a cast-concrete projecting shelf. The rain landing on the coping directed all of the water to the outboard edge, which ends at a mortar joint. The walls were wet. That’s stupid. However, the building didn’t fail until it got spray-foamed, because it was able to dry out. But once it was insulated, the building had bad freeze/thaw damage in just two years. It failed because it’s located in a cold climate and the building had really stupid detailing.”

Deal with the rain

The moral of the story is: If you aren’t willing to manage bulk water issues, don’t bother to insulate your brick building. “You need to deal with the rain,” says Brennan. “You need to do everything you can to keep the rain off the wall. If there are ledges, you want copper flashing to shed it off the ledge — flashing with a projecting drip-edge.”

Building scientist Joseph Lstiburek agrees. “You can insulate walls to a great extent if water isn’t concentrated on the surfaces,” says Lstiburek. “So the first thing that you do before you do any insulation is you install your drip edges, you deal with your flashings, you deal with the rain shedding things that will basically kick the water off of the surface.”

Assess the bricks

Bricks vary. Lstiburek says, “Some brick is really bad, some brick is pretty bad, some brick is pretty good, and some brick is great.”

At the Building Science Corporation, John Straube and Chris Schumacher have been researching which types of tests are most useful. They have developed a testing protocol to determine the thermal conductivity and freeze resistance of bricks. “We now have a test method that allows us to look at the load and the response of the materials,” says Chris Schumacher. “There is a critical degree of saturation at which freeze/thaw damage occurs. You can test the brick to quantify the point at which the material fails. You want to establish a limit for moisture content during freeze/thaw.”

Don’t assume that all of the bricks in your building are identical. “The best bricks were often used on the exterior,” notes Straube. “If I take a brick sample from the exterior, it may be different from the brick sample from the interior.”

Although it’s a good idea to test bricks from all of the wythes in the wall, the inner wythe is often the most crucial one to test. “After you insulate, the biggest change is in the interior side of the masonry,” says Straube. “The outer wythe has always been cold in winter, but now the inner wythe might for the first time flirt with 32 degrees or lower in some climates.”

Hygrothermal modeling

Once your bricks are tested, you’ll have a good idea of their vulnerability to freeze/thaw damage. You’ll also have some values that can be plugged into a hygrothermal modeling program like WUFI.

However, few energy consultants are WUFI experts. Users of WUFI must be careful of the “garbage in, garbage out” problem. When it comes to WUFI, remember: don’t try this at home. “WUFI modeling can guide decision making,” says Straube. “But WUFI modeling requires knowledge, comparison to measured data, and real experience.”

Climate matters

WUFI modeling uses climatic data to model moisture and thermal flows through building assemblies. In general, brick walls in cold climates are more susceptible to freeze/thaw problems than brick walls in warm climates.

“It’s rare that we have to worry about freeze/thaw problems in places like New Jersey and New York City,” says Lstiburek. “I don’t think we have much to worry about in Boston. But I’d be real nervous in Burlington, Vermont, and I’m real nervous in Ottawa, and I’m kind of semi-nervous in Toronto. … When we start getting into, say, Portland, Maine, I’m going to say you probably shouldn’t insulate more than R-10.”

One more worry: embedded beams and joists

The exterior walls of many old multi-wythe brick builders are used to support beams and joists. If the building is insulated on the interior, the ends of these embedded beams get colder — and therefore wetter. Moreover, less energy is available to help them dry out.

“Embedded wood timbers can rot,” says Straube. “Wood and steel are both moisture-sensitive. If steel corrodes, it expands — and that is a problem. There are a number of techniques to address embedded beams. You can inject the wood with borate salts to preserve the wood. You can insert metal wedges to conduct heat to the end of the beam. You can install hot water pipes to heat the end of the beam. Finally, there’s the practical Yankee solution: you build a load-bearing wood wall to support the beam, and then you fire up your chainsaw and cut off the end of the beam.”

Almost all of the solutions to the embedded beam problem have drawbacks except the chainsaw solution.

What type of insulation? And how thick?

Most people assume that you need thicker insulation in a cold climate than a warm climate. While that makes sense for wood-framed buildings, it isn’t necessarily true for an old brick building. In general, brick buildings in cold climates get less insulation than buildings in warm climates. (Thinner insulation allows more escaping heat, keeping the bricks a little warmer and safer. Moreover, in some cases, thin insulation can allow some drying to the interior.)

“So the question is, ‘Well, how much insulation can I add before I get into trouble?’” says Lstiburek. “You’re going to hate this answer or love this answer — depending on whether you’re a client or a consultant. The consultant’s answer is, ‘It depends.’”

Clearly, fiberglass batts should never be used to insulate the interior of a brick wall. (Since fiberglass batts are permeable to vapor and air, they permit interior moisture to condense on the cold bricks. That’s bad.) Most experts agree that the best insulation for the interior of an old brick building is closed-cell spray foam. In most cases, the foam is sprayed directly against the interior side of the brick. To determine how thick you can go, you’ll need to talk to your consultant. “We take samples of brick and send them to John Straube for the hot and cold soak test,” says Brennan. “Then he does WUFI modeling. We generally end up installing about 3 inches of closed-cell foam.”

It’s possible to insulate the interior of an old brick wall with rigid foam; if you want to try this approach, a useful resource is a U.S. Department of Energy document, . Even though this publication provides guidance on installing rigid foam, the authors note that “closed-cell polyurethane foam … sprayed directly onto the brick masonry … is the most effective, though costly, method for insulating the interior of brick walls.”

If the building is vulnerable, don’t insulate the walls

In some cases, your consultant may advise you that it’s best to leave your walls uninsulated.

“Sometimes you just don’t insulate the walls,” says Straube. “Even if the walls are left uninsulated, you can often reduce heating demand by 50% by addressing air sealing, the basement, the roof, and the windows.”

Can I use cellulose?

Some energy experts have insulated old brick buildings on the interior with cellulose. One of the pioneers of this technique is Chris Benedict, a New York City architect.

Benedict described her technique in an article published in the March/April 2010 issue of Home Energy magazine. “In 1998 I started specifying a wall assembly for masonry buildings comprised of 2 5/8-inch metal studs at 16 inches on center, front face of the studs 4 inches or 5 inches (depending on the construction budget) out from the interior face of the existing masonry wall, covered in 5/8-inch gypsum board,” Benedict wrote. “The gypsum board was carefully sealed with caulk to the subfloor at the base of the wall, brought up between the wood joists to the underside of the subfloor above, and sealed. Dry cellulose insulation was then blown into the 4-inch or 5-inch cavity at 3 1/2 lb. per cubic foot density, giving a true R-14 or R-17.5. For the vapor barrier I used flat wall paint, nothing else! All holes in the ADA were sealed. … to date I have yet to see a masonry building destroyed by insulating it.”

Like other experts interviewed for this story, Benedict emphasizes water management. “As part of the scope of my work I make sure that the wall is pointed and in good repair,” she wrote. “The building is thoroughly assessed for any damage to bricks and mortar inside and out. … If a building is showing any problems with liquid water management, these problems must be resolved prior to insulating.”

I asked John Straube how he felt about Benedict’s technique. “I have qualms,” he told me. “But if the air sealing is done right, I don’t think there is a problem. First you have to walk around the building and see if it leaks. Then you ask, can I get it airtight? You need to install a fluid-applied membrane that is vapor-permeable but airtight on the interior surface of the bricks.”

Straube prefers closed-cell spray foam. “One thing about spray foam: it does a really good job or air-tightening, as well as some water tightening,” he says.

More maintenance

According to Bill Rose, a research architect at the Building Research Council at the University of Illinois, anyone who insulates the interior of an old brick building should plan to inspect the exterior on a regular schedule.

Rose imagined a conversation with a building owner. “People say, ‘We have a mandate to put insulation on our walls. How much damage will happen to this building if we insulate at the interior?’ I say, ‘If you do that, during winter the exterior materials will be wetter than they used to be.’ So then I’m asked, ‘What is the range of damage?’ And I say, ‘Everything falls into the maintenance range. You’ll need to increase the maintenance budget.’ There is uncertainty, but I’m happy to go forward if we include the concept of increased maintenance. That’s how we address worry problems. We have to have more eyes on what happens.”

Can I go forward without a consultant?

If you own a building with low risk factors, you may decide to go ahead without hiring a consultant.

An example of a building with low risk factors would be a building in Philadelphia with no signs of exterior water damage, without any deteriorating bricks, and with flashings that do a good job of keeping rainwater off the building.

Last week’s blog: “Utility-Scale Wind Turbines.”

102 Comments

  1. James Brown | | #1

    fiberglass
    "Clearly, fiberglass batts should never be used to insulate the interior of a brick wall."

    is fiberglass so bad? Even when used with a good vapour check on the interior? It will allow the wall to dry to the inside, will closed-cell spray foam allow this?

  2. Kevin Dickson, MSME | | #2

    Foam Injection
    Denver's most respected home energy upgrading contractor has been injecting foam into brick walls for years. In a double wythe wall, you can sneak in an inch of foam for an R value of 6+.

    Dennis Brachfeld of AAS reports no moisture problems (Denver is relatively dry) and much increased comfort. It's a very expensive procedure, even without building a new interior wall, so they rarely do an entire home, just the most uncomforable rooms.

    In my own testing, I found that the "blue can" Great Stuff (low expansion) fills the wythe cavity much better than the cheaper, standard "red can" stuff.

    Note: foam injection may cause worse problems even than insulation on the inner wall. That's because it plugs the cavity behind the exterior bricks. This cavity is traditionally relied on to help drain and dry the brick. So stay away from this method if you have rain in the day with freezing at night.

  3. User avater GBA Editor
    Martin Holladay | | #3

    Response to James
    James,
    Q. "Is fiberglass so bad?"

    A. Yes. It is almost impossible to make drywall so airtight that interior air will never contact the bricks and lead to condensation.

    Q. "Even when used with a good vapour check on the interior?"

    A. The problem has more to do with air leakage and air convection than vapor diffusion.

    Q. "It will allow the wall to dry to the inside."

    A. Precisely my point -- you don't want to allow vapor diffusion to occur between the warm, interior air and the cold bricks -- a vapor-open assembly is counterproductive.

    Q. "Will closed-cell spray foam allow this?"

    A. No, and that's a good thing.

  4. James Brown | | #4

    fiberglass again
    I ask because you don't advocate interior polyethylene barriers because that stops the wall drying to the inside, but you are advocating closed-cell foam which will also stop the wall drying to the inside. Am I misunderstanding something? I don't want to install the wrong material in my renovation. No one over here (UK) uses spray foam on bricks, most use closed-cell foam boards.

    Also perhaps cellulose has worked (as mentioned in the article) as it has vapour resistivity between mineral wool and closed cell foam. (I'm using figures for resitivity from the following document , pg 3 and 4). However, the cellulose manufacturer does not recommend cellulose on solid masonry walls.

    By the way you might be interested in some of the projects on that site (eg the solar slab).

  5. User avater GBA Editor
    Martin Holladay | | #5

    Response to James Brown
    James,
    You're right -- I don't advise the use of interior poly in most climates. However, interior poly makes sense in much of Canada and Alaska -- at least on the interior of wood-framed buildings.

    Load-bearing brick walls differ in many ways from wood-framed buildings, however, as I try to make clear in the article. I don't think you should use any rules of thumb from wood-framed construction when insulating an existing building with load-bearing brick walls. In case you are wondering, I don't advocate the use of interior poly when insulating brick walls.

    Rigid foam boards can be used to insulate the interior of a brick wall, as long as the seams between the sheets are carefully sealed with caulk, canned foam, or tape. All of the other advice in the article above would still need to be followed: deal with the rain, assess the bricks, consider the climate, and don't install too much insulation.

    Cellulose insulation differs in two important ways from fiberglass batts: dense-packed cellulose does a much better job of limiting air infiltration than batts, and cellulose is hygroscopic. If you were to use fiberglass batts to insulate a cold brick wall, condensation could run down the brick wall and pool on the floor. If you install cellulose -- still an experimental method, and probably risky in cold climates -- the cellulose is able to absorb and store a certain amount of moisture that might otherwise condense against the cold bricks. If the wall assembly allows drying to occur at a faster rate than moisture accumulation -- something that can be determined by WUFI -- such walls can succeed. Perhaps.

  6. James Brown | | #6

    fiberglass
    thanks Martin. I've got a better grip on the issues now.

  7. James Brown | | #7

    cellulose
    I know cellulose is best applied damp with a blower machine but these can't be rented in the UK. Is it feasible to mix the cellulose with say, a paddle mixer in a big bucket, adding water and then apply it by hand, a bit like rendering/harling/plastering? This would be for filling the gaps between studs before drywalling over.

  8. User avater GBA Editor
    Martin Holladay | | #8

    Response to James Brown
    James,
    I don't recommend your suggested technique, for a variety of reasons. The technique introduces too much water; you won't be able to fill all the gaps; and the density of the installed insulation will be too low.

    Insulating the interior of a brick wall is tricky. You want a carefully air-sealed assembly. If you want to insulate with cellulose -- I method I don't recommend -- then I suggest you take John Straube's advice: "You need to install a fluid-applied membrane that is vapor-permeable but airtight on the interior surface of the bricks." This is not a method that is appropriate for do-it-yourselfers who spread gobs of insulation with their hands.

    My advice is to hire an insulation contractor experienced at insulating brick walls.

  9. Buildingwell .org | | #9

    Extending existing buildings
    This article brings up a number of good points about insulating brick buildings to help extend their lifetimes. While it's true that the preferred method would be to insulate the exterior, there are a number of reasons that may be impossible - many times related to historic reasons such as for credit, zoning or funding. Insulating the interior as you've stated really comes down to "it depends" which is probably the best way to put it. A professional can be most helpful in determine whether the interior insulation is really the best thing for the brick building and if so, to what extent. In the end, the deciding factor should be the cost and life-cycle assessment for your options.

  10. Robert Haverlock | | #10

    insulating brick house from outside with foam
    As I understand it, your saying insulate from the inside, but not outside. I witnessed a foam company insulate from the outside by drilling holes in the gaps 16in on center, Does this, or could this not also fill up any rain plaine designed into the home? And I have not read in this blog anything about rain plaines being involved? Here in Seattle Washington.

  11. User avater GBA Editor
    Martin Holladay | | #11

    Reply to Robert Haverlock
    Robert,
    All of the information in this article is about multi-wythe load-bearing brick walls. Such walls were commonly built in decades past; most such buildings in the U.S. are between 90 and 200 years old.

    Your comment mentioned "rain planes." I assume that you are referring to the drainage gap in a brick veneer wall. Brick veneer walls are built completely differently from mult-wythe load-bearing walls. The typical brick veneer wall is non-structural. A single wythe of bricks is installed; between the brick veneer and the wall sheathing is a drainage gap that shouldn't be blocked or filled. Most brick veneer buidlings are actually wood-frame buildings; the wood-frame wall is the load-bearing wall.

    If any insulation contractors are installing spray foam in the drainage gap of brick-veneer walls, they are making a mistake. These drainage gaps should not be filled.

  12. James Brown | | #12

    cellulose
    "you won't be able to fill all the gaps; and the density of the installed insulation will be too low"

    It seems unlikely to me that the machine could apply the cellulose with more force than I could apply by pushing it on with a hawk and trowel (or similar, eg tamping it. Or, as you say, literally with your hands!) This is for a situation where you have yet to sheet over the stud walls. I'm not suggesting it would be possible to fill a cavity via holes by hand successfully.

    "My advice is to hire an insulation contractor experienced at insulating brick walls"

    Over here that would result in laminate foam board, or foam board in stud bays then drywalled over. This method has too many detailing requirements to leave to a contractor. I think the spray method ('liquid applied' as you referred to it) is great as it as it would ensure a full fill. My main reluctance to use sprayfoam is the risk it poses to joists / timbers embedded in the masonry. I feel cellulose may buffer the humidity and help move water away from the structural timbers to avoid them rotting.

  13. Eric Novotny | | #13

    Good Read
    Very good read and even. We don't have to worry about many of these issues in my climate region but I thought the article, and follow up, was well done.

  14. Eric Dymond | | #14

    Silane Water Repellent?
    Couldn't you minimize the amount of moisture penetration by using a silane/siloxane water repellent? That would allow the brick to dry to the exterior while preventing moisture intrusion.

  15. User avater
    Jim Baerg | | #15

    Insulating between the wythes
    Hello, very timely subject for me. I've got a double whythe, load bearing house and would like to place insulation between the whythes in the 2.5-3 inch gap. Preserve the exterior and avoid a complete interior remodeling job are the reasons. Plus fantastic thermal behavior in the summer with the added mass.
    Location is dry and cold, 12 inches of precip/year, half in snow. 8000HDD. Absolutely no sign of moisture related deterioration anywhere in the house. The roof is steep and has gutters but the bricks are pretty soft. Interior is plaster directly on the brickj and the basement is dry.
    So, I've looked at UF, Air Crete and low rise 2 part foam primarily because they can be injected in the mortar joints. Part of the difficulty is finding an applicater.
    What would you recommend in terms of insulating the void? Can it be done safely and what type of insulation would you recommend.
    Attached is a photo.
    Thanks, Jim Baerg

  16. User avater GBA Editor
    Martin Holladay | | #16

    Response to Eric Dymond
    Eric,
    In general, historic preservationists and most building scientists agree that, although silane/siloxane coatings may have their applications for specific problems, they should not be used as a general solution to try to improve the hygrothermal performance of all of the walls of an existing building. Their performance and longevity are questionable.

  17. User avater GBA Editor
    Martin Holladay | | #17

    Response to Jim Baerg
    Jim,
    My advice to you is the same as the advice presented in the article: hire a consultant experienced in these issues, and have your bricks tested. (Although if you are unable to locate a contractor willing to do the work you propose, the entire issue may be moot.)

  18. Marcus De La Fleur | | #18

    Lime wash as water repellent?
    Eric asked above about silane/siloxane water repellent. While discussing this topic with a restoration mason, he mentioned lime wash, which is apparently suitable for old(er) load bearing masonry walls. Each lime wash application lasts only for a few years, but it is said to improve the hygrothermal performance of the wall. Any opinion on this option?

  19. Kohta Ueno | | #19

    Internal Insulation of Masonry Walls Measure Guideline
    If anyone is interested in BSC's current document on the subject, our Building America-sponsored research report has recently been finalized:

    RR-1105: Internal Insulation of Masonry Walls: Final Measure Guideline

  20. User avater GBA Editor
    Martin Holladay | | #20

    Response to Kohta Ueno
    Thanks, Kohta. I've added a link to the document in the "More Information" sidebar.

  21. Randy Starr | | #21

    I know this article is a bit
    I know this article is a bit old, but are these concerns basically limited to cold climates? I am down in New Orleans where it only freezes occasionally in the winter but we do have a ton of moisture (both bulk and vapor). Is this freeze/thaw concern really only a problem in the North with repeated and extended freezing / thawing cycles?

  22. User avater GBA Editor
    Martin Holladay | | #22

    Response to Randy Starr
    Randy,
    Yes, these concerns are limited to cold climates. As building scientist Joe Lstiburek, who was quoted in the article, said, “It’s rare that we have to worry about freeze/thaw problems in places like New Jersey and New York City.”

    None of the concerns mentioned in this article apply to buildings in New Orleans.

  23. Randy Starr | | #23

    Awesome. Thanks.
    Awesome. Thanks.

  24. Matthew Emerson | | #24

    Philadelphia
    Thank you for writing this article. My wife and I are currently looking to relocate to another home in Philadelphia, which of course, means old double-wythe construction! As we look I'll pay closer attention to the brick conditions on the exterior, particularly around chimneys and parapets. I found it interesting that you referenced Philadelphia as an area that wouldn't be a problem to insulate from the interior. I would still be a little wary of adding too much insulation, as there can be prolonged periods of wet winter weather, especially the last few years. Additionally, I disagree with the EIFS recommendation, as I believe it's an inferior product as well as a dangerous one. Here in Philadelphia there are a lot of contractors installing it, only to have it redone shortly after. Many times, it's the installation and flashing detailing, etc. I will personally be looking into mineral wool open joint rainscreen on the rear / side where the street presence isn't as important to the block conformity.

    Any articles on insulating attic spaces? I know there are a lot of flat-roofed homes in the Northeast that are un-insulated in the tight void space between the roof and ceiling.

  25. User avater GBA Editor
    Martin Holladay | | #25

    Response to Matthew Emerson
    Matthew,
    The best way to insulate a flat or low-slope roof is with a layer of rigid foam above the roof sheathing. That means that insulation upgrades are usually performed when it is time to install new roofing.

  26. Eddy Trochez | | #26

    Following the question about a flat roof.
    Will Roxul and a vapor barrier be a good solution for a flat roof (NYC area)? Will this method cause problems with the embedded wood joists in a load-bearing brick wall? I will not insulate the walls, only the ceiling and overlap the vapor barrier a few inches with the wall. Thanks in advance.

    Eddy

  27. User avater GBA Editor
    Martin Holladay | | #27

    Response to Eddy Trochez
    Eddy,
    In the response posted on this page immediately above your question, I wrote, "The best way to insulate a flat or low-slope roof is with a layer of rigid foam above the roof sheathing."

    If you want to insulate below the sheathing, I recommend that you use closed-cell spray foam.

    Roxul is a bad choice because it is air-permeable. It can allow warm, moist interior air to reach the cold roof sheathing, leading to condensation.

    A polyethylene vapor barrier is not recommended for this application. It will not prevent air movement from the interior to the sheathing. It's impossible to install poly in a way that is totally airtight -- and in any case the trapped air would inevitably have moisture in it anyway.

  28. Eddy Trochez | | #28

    Thanks Martin for the help.
    Thanks Martin for the help. Some people are installing rigid foam bellow the sheeting and sealing the edges with foam or caulk. How do you feel about this approach?

  29. User avater GBA Editor
    Martin Holladay | | #29

    Second response to Eddy Trochez
    Eddy,
    That approach -- sometimes called "cut and cobble" -- can work, but it has two disadvantages:

    1. Obtaining an airtight installation (which is essential) is fussy, time-consuming work.

    2. Even if the work is perfect, you still have thermal bridging through the rafters.

  30. Eddy Trochez | | #30

    Thanks Martin
    Martin,
    I was doing some reading (your article here on GBA) regarding the possible health issues with spray foam. The situation definitely makes it more difficult for the DIYer, and the cost to hire a professional is sometimes astronomical for this type of job. What kind of advice would you give to somebody who wants to do it himself? Is it worth it? I'm convinced that spray foam is the way to go in my situation, but the thought of having lingering fumes and smells is very scary.

  31. User avater GBA Editor
    Martin Holladay | | #31

    Third response to Eddy Trochez
    Eddy,
    Only you can make that decision. You have to weigh your expected energy savings against the expected cost of the work, and decide whether you feel comfortable using spray foam. It doesn't matter what I think -- only what you think.

    The best approach is to combine new rigid foam on top of the roof sheathing with a re-roofing job.

  32. Eddy Trochez | | #32

    Thanks Martin
    If it wasn't for this site, I would've made a big mistake. Local contractors wanted to blow in insulation.

    Question regarding the rigid foam.
    Will I need a second layer of sheathing on top of the rigid foam? Can you point me to a good online resource on the subject?

    Thanks a million,
    Eddy

  33. User avater GBA Editor
    Martin Holladay | | #33

    Fourth response to Eddy
    Eddy,
    No, you don't need any sheathing on top of the insulation. Here are two articles to help you:

    How to Insulate a Low-Slope Roof

  34. Joanne Alfonsi | | #34

    Spalling
    If old brick walls are patched and repointed with cement based mortar they spall. Spray foam insulation becomes extremely hard and impermeable (like a cement based mortar). if the spray foam is applied to the interior would it not cause the same spalling problem on the interior of the wall. would it be better to apply a rigid foam insulation board and then an inch of spray foam. Would you for see any problems with this method? I would be reluctant to spray directly onto the brick. This would be an R value of 12 or so. We are based in Toronto and our bricks appear in great condition (even in the chimney)

  35. User avater GBA Editor
    Martin Holladay | | #35

    Response to Joanne Alfonsi
    Joanne,
    The problem you describe -- repointing an older brick building (most of which have lime-based mortar) with Portland-cement-based mortar -- is independent of the problem described in this article (insulating an older multiwythe brick wall on the interior). Obviously, there is more than one way to damage an older brick building. Choosing the wrong repointing mortar is one way to damage it. Insulating it incorrectly is another way.

    I stand by the advice given in this article. If you want to insulate a brick wall on the interior, follow all the steps listed in this article before you proceed. If you are sure that it is safe to proceed, then closed-cell spray polyurethane foam (sprayed directly on the interior of the bricks) makes more sense than rigid foam.

  36. S. Tunji Turner | | #36

    Philly Double Wythe Detail
    Hey all, just finalizing on a wall detail for my breezeway double wythe brick wall. I would add 2" polyiso foam board with reflective side showing, with a open joint rain screen system ( Hardie Panel,etc). My inside was my greatest concern. I have decided to frame 1.5" away from the interior brick, with 1 " spray foam sprayed directly on the brick, and then denim insulation in the 2x4 cavity 16"oc. And 3 mil plastic sheathing before 1/2" sheetrock. Any suggestions/advice would be appreciated, thx

  37. User avater GBA Editor
    Martin Holladay | | #37

    Response to S. Tunji Turner
    S. Tunji Turner,
    My advice hasn't changed since I wrote the article. So: if you are leaving the exterior bricks exposed, the only insulation to consider is closed-cell spray polyurethane foam. And that should only be used if you feel confident about your exterior water management details and the quality of your bricks.

    If you are willing to cover up the exterior bricks -- and it sounds like you are -- I would put all of the insulation on the exterior of the building. Two inches of polyiso is better than nothing, but I would aim for at least 4 inches of polyiso if I were you.

  38. S. Tunji Turner | | #38

    Response to martin
    So you are suggesting 4" exterior with a rain screen , soffit box, water management. and then no foam on inside, just the denim insulation on the inside w/plastic.

  39. User avater GBA Editor
    Martin Holladay | | #39

    Response to S. Tunji Turner
    S. Tunji,
    No denim insulation. No interior polyethylene. Otherwise, you've got it.

  40. Anita B | | #40

    Brick walls in Arizona
    Hi- I hope this blog is still active.
    We live in a 1961 brick house in Tucson, AZ, without any insulation of the exterior brick walls. Brick is about 4-inch thick (yes, we basically live in a brick oven). We would like to insulate inside. I don't think we have to worry about the freeze/thaw problems, but not sure what materials do use. Some folks here that have experience say, fiberglass batts are just fine and less expensive. We also looked at the rigid foam-sheets.
    Any advice?

  41. User avater GBA Editor
    Martin Holladay | | #41

    Response to Anita B.
    Anita,
    In your climate, you can insulate the interior of your walls without worrying about freeze/thaw damage.

    I don't recommend that you install fiberglass batts, for two reasons: (1) Fiberglass batts perform worse than all other insulation types, and (2) If they were insulated with fiberglass batts, your walls would be susceptible to inward solar vapor drive problems, especially if your house has air conditioning. (For more information on inward solar vapor drive, see When Sunshine Drives Moisture Into Walls.)

    I advise you to install rigid foam insulation on the interior of your walls. Polyisocyanurate insulation is the most environmentally friendly type of rigid foam insulation, and it has the highest R-value per inch. Polyiso performs well, and it will prevent any problems from inward solar vapor drive.

  42. Jeff Speirs | | #42

    Vermiculite
    Excellent article!
    I have an 180 yr old house with load bearing brick walls in the Philadelphia area. The bricks have an exterior layer of stucco which has been painted. The house roof has a 2 1/2' overhang which keeps the walls fairly dry. The foundation is also brick and this allows some moisture to wick up into the above grade brick. The interior plaster is applied to lath on top of 1" thick furring strips. the gap created by the furring stips is open from the basement to the attic. Would it be advisable to insulate and/or seal the top and bottom of this 1" gap? If so, would vermiculite be an option? It seems like the easiest material to flow down into that narrow space.

  43. User avater GBA Editor
    Martin Holladay | | #43

    Response to Jeff Spiers
    Jeff,
    While some people have used vermiculite to insulate the type of gap you describe, I don't recommend the practice.

    The main problem with vermiculite is that it does little to stop air flow. If your gap is open from the basement to the attic, the most critical step for you to perform is air sealing. Every single channel needs to be carefully sealed in the basement as well as the attic. Unless you are planning to demolish your interior plaster, this work will need to be performed in the basement and attic, using a two-component spray foam kit.

    One inch of air-permeable vermiculite wouldn't provide much R-value anyway.

    Since the exterior of your building has been stuccoed, the best way to insulate the building is with an exterior layer of rigid foam. The most economical way to do this would be to finish the exterior with EIFS (rigid foam plus synthetic stucco). If you call up a few local EIFS contractors, you should be able to get bids for the work.

    If you prefer to do the work from the interior, I recommend that you follow the advice in the article, by installing spray polyurethane foam against the interior of your brick walls. That will require you to demolish the interior plaster.

  44. Diane McAvoy | | #44

    Freeze/thaw concerns in DC?
    The article and commentary have been so helpful for my current predicament. I bought a 100yr. old double wythe end-unit row house about four years ago that had been flipped. This past spring the house started to feel very humid. I started to notice mold in my closet (on an 2nd floor exterior, northern wall). After several consultations with an industrial hygienist, we started to discover more mold on the western and northern walls where the air was stagnate (behind pictures, closets, etc). We determined that the mold was caused by a vapor drive issue from the exterior brick. It was getting caught in middle of the wall and then condensing in the cooler months, not drying, and then providing the conditions for mold to grow inside the wall the spring/summer. The mold I saw behind my pictures was because the drywall was saturated with water. When they flipped the house, they applied drywall directly to the old plaster without a vapor barrier. In some cases there was also wallpaper attached to the plaster and then drywall over it....a recipe for disaster that I am now living out.

    I have performed the mold remediation steps and am now left with very old plaster and in some areas just brick where the plaster has fallen off. My next task is to figure out how to rebuild in a manner that will prevent vapor drive to the inside AND reduce the risk of condensation inside the wall structure. While I've consulted with several structural engineers and performed lots of internet research (love building science articles), I'm still not confident of the best way to address the issue without causing unintended consequences.

    The first step I am taking is to remove the remaining plaster and repoint the interior brick with Type N lime mortar and then apply a brick sealer on the interior. My current plan to finish the wall is to frame out the inside using 1.5" x 3.5" studs, leaving about an inch gap between the frame and the brick and the framing oriented like in the picture below (my current kitchen). From there, I wanted to hire a spray foam contractor to apply 2" of closed-cell spray foam insulation that would fill in the 1" gap behind the framing plus about an inch into the frame cavity. After that, I would reapply drywall. I think this would address both my vapor barrier and condensation concerns, but I am not sure how it would address the freeze/thaw concerns. I read it is not a concern in NYC, so I assume DC is fine to use this method. Do you see any red flags with my approach? This is not my area of expertise and I've found that different people have lots of different opinions. This is all really expensive and unexpected, so I only want to do this once, so am just looking for some validation that I am on the right track. Thank you so much!

    Diane in DC

  45. User avater GBA Editor
    Martin Holladay | | #45

    Response to Diane McAvoy
    Diane,
    Your case raises many questions.

    First of all, the climate in your location (Washington, DC) is mild enough that you really don't have to worry about freeze/thaw damage to your bricks. In general, it should be safe to insulate the interior of your walls with closed-cell spray polyurethane foam.

    But your mold situation is unusual, and the actual mechanism is a little puzzling. I suspect that two factors may be at work here: the exterior of your bricks may be unusually wet -- which would be the case if your house had insufficient roof overhangs or some type of flashing problem -- and (perhaps) the interior finishes on the walls were vapor-impermeable. (The classic problem occurs with vinyl wallpaper, which is a disaster if used in an air-conditioned home in a humid climate.)

    In your climate, an uninsulated brick wall doesn't usually grow mold. During the winter, the indoor air is usually dry, and the bricks are kept warm by your heating system. During the summer, if the house is air conditioned, the indoor air is dry, and any moisture in the bricks dries inward -- unless, of course, there is vinyl wallpaper to mess things up.

    Without a site visit, I can't know what's going on at your house, of course, and you shouldn't take any action based on my speculation.

    You shouldn't proceed with a remedy, in my opinion, until you fully understand the mechanism that created the mold. It's possible, for example, that your house has a wet basement or a wet crawlspace, and that the mold grew during the winter; this might have happened if all of the rooms of your house weren't heated.

    Any remedies have to start with the basics. You need to do everything you can to keep rain off of your bricks, and that might require better roof overhangs. And you need to be sure that you don't have a wet foundation.

  46. Diane McAvoy | | #46

    Thanks
    Thank you for your comments, Martin. I will look into other factors that may have contributed to moisture accumulation in the wall besides just vapor drive-related moisture getting stuck and condensing in between the plaster and paper-backed drywall. I'll keep you posted. Best, Diane

  47. User avater GBA Editor
    Martin Holladay | | #47

    Response to Diane McAvoy
    Diane,
    It's impossible for moisture to "get stuck and condense between plaster and paper-backed drywall." Paper-backed drywall is hygroscopic and vapor-permeable. When it gets wet, it dries rapidly to the interior of the house -- unless someone installed vinyl wallpaper, or unless someone glued a mirror to it.

  48. Colin Marshall | | #48

    We recently purchased a 2.5
    We recently purchased a 2.5 story brick masonry home in Chicago that we plan to renovate. Upon demolition of the kitchen, I discovered moldy batt insulation between a plastic sheathing (the last renovator's vapor barrier form 1983?) After reading your article, and the ones on BSC this made sense. I raised the issue with my architect and asked how we should address and this was his response...

    "We have typically installed a vapor barrier on the inside face of the masonry wall with 2" rigid foam insulation between wood or metal studs, and then we use a secondary vapor barrier on the inside face of the studs (between the studs and the gypsum board). Properly installed, this isolates the insulation and framing from condensation or water infiltration from either side of the interior wall assembly. Rigid foam is considerably more expensive than batt insulation (when calculated as dollars per R-Value) but I will investigate the cost of spray on insulation (I have pricing estimates from another project that I can reference). My concern is that spray on insulation will prevent the masonry wall from properly breathing thus trapping moisture in the wall and causing efflorescence and deterioration of the masonry."

    1) Can you recommend any consultants in Chicago?
    2) Is it time for a new architect?

  49. User avater GBA Editor
    Martin Holladay | | #49

    Response to Colin Marshall
    Colin,
    Sandwiching insulation and studs between polyethylene doesn't work, because it's impossible to make the poly layers completely airtight, especially on a job site. (Even in a university lab, it would be a difficult challenge.) Changes in temperature and air pressure will cause a pumping action that leads to air exchange between the air trapped between the polyethylene layers and the air on the exterior or interior side of the sandwich assembly. When humid air enters the sandwich assembly, it can trap moisture between the poly layers. Later, when one side of the poly sandwich gets cold, water will condense on the poly and run down to the bottom of the sandwich, and will pool at the bottom plate.

    Spray polyurethane foam insulation is the recommended insulation material to use on the interior of a multi-wythe brick wall -- subject to the caveats listed in this article.

    The sentence, "My concern is that spray on insulation will prevent the masonry wall from properly breathing thus trapping moisture in the wall and causing efflorescence and deterioration of the masonry" doesn't make any sense. If the architect wants the brick wall to "breathe" to the interior, why is he suggesting the installation of polyethylene -- a layer that limits "breathing"? Clearly, a multi-wythe brick wall that is insulated on the interior will "breathe" (I would say, will dry) to the exterior, not the interior. There are still risks, of course, especially in freezing climates. These risks are explained in the article.

    If you want to hire a consultant, the consultant doesn't have to live in Chicago. It's hard to beat the consultants at the in Somerville, Mass., or at in Waterloo, Ontario.

    Only you can decide whether it's time for a new architect. It sounds like your current architect will need a little hand-holding or guidance because of an incomplete knowledge of building science. Unfortunately, that's not unusual -- so switching architects may not help.

  50. Owen Sechrist | | #50

    mortar and paint
    In my local many of the buildings are over 100 years old and were constructed with a very soft brick and limestone mortar with no portland cement. My understanding is that because the combination of soft brick and self-healing mortar allows for resiliency in freeze-thaw cycles.

    When I observe buildings with damage to the brick it is often caused by either direct water/drainage issues or re-pointing with hard portland based mortars.

    Is soft brick and limestone mortar more resilient to being insulated on the interior?

    How does exterior painting affect the insulation scenario?

  51. Iain Whyte | | #51

    Confused and uncertain!
    In the UK, spray foam is very rarely ever mentioned yet given the large number of old houses with 9" walls there is a lot of opportunity and much of what you read is conflicting or not well thought through. The simple fact seems to be ask 3 experts and you get three different opinions and each is convinced he is right. I have a 220 year old brick barn with solid 18" lower walls and 13" upper walls, no damp proof course. The weather here is fairly benign with around 22" rain per year and temperatures rarely move outside of a -5 to +25 range with a median around 15 degrees centigrade. Timber joist ends sit directly in the walls bedded in using the same lime mortar that the walls are built with. I have read many many many articles, spoken to a lot of 'experts' and suppliers and have yet to get a consistent picture of what should be done. Some advocate a woodfibre board or a silicate board essentially glued to the wall to provide a vapour open insulation only some 50mm thick so that enough heat leaks through to keep the inside face of the wall above freezing. Others say seal it all up with a PIR type vapour proof board - but the air will still leak through the woodworm holes and old buidings are impossible to seal adequately. So my thinking is to go the vapour open route in conjunction with a central ventilation system to keep dry air moving around inside and allow any excess moisture to evaporate out of the wall into the house and when the sun shines and the wind blows, the outside will dry naturally. The real dilemna here is that I am not sure that I can do nothing e.g. leave the walls uninsulated (even though that's what the conservation people would like) as the heat loss is so high we would need to round in ski-suits in winter in order to keep heating bills down.

  52. User avater GBA Editor
    Martin Holladay | | #52

    Response to Iain Whyte
    Iain,
    I sympathize, but I'm sorry to say that I cannot deviate from my advice. It's unwise to try to invent new ways to insulate this type of building, especially if there are embedded beams or joists.

    Of course, the best way to insulate this type of building is on the exterior, with a layer of exterior rigid foam protected by synthetic stucco (EIFS), or mineral wool panels and synthetic stucco.

    Good luck.

  53. Jason Cuve | | #53

    Brownstone
    We are renovating a circa turn of the century Brooklyn brownstone. The only walls we were considered insulating were the front and back brick walls. There are no joists or beams embedded into these two exterior walls. They are about 17 feet across. My question is, if the facade is covered by a layer of brownstone, does the brownstone provide any insulation or water protection to the bricks behind?

    The back wall is painted white from the outside. Looks like it has been repainted many times. There are no leaks or issues I can detect on the inside of the walls. We have them currently exposed after demolition. We have not discussed the type of insulation with our contractor. After reading your article I am prepared to tell him to go with closed-cell foam. I will note, we have not had a specific brick consultant come out, but we have had several engineers look at the place who said nothing about insulation concerns.

    Oh, and another question. Is insulating the cellar brick walls an issue at all? They are mostly, though not completely, underground.

  54. User avater GBA Editor
    Martin Holladay | | #54

    Response to Jason Cuve
    Jason,
    The easy question first: I don't think you'll have any problems resulting from insulating the cellar walls, although it's always possible that you'll see some spalling or freeze/thaw damage of some of the above-grade exterior bricks (if there are any).

    When it comes to brownstone, I'm going to have to plead ignorance. I suggest you consult local experts familiar with brownstone. If you can't find a local expert, you could work with the Building Science Corporation.

  55. Rich Steenwyk | | #55

    Triple Wythe Wall Question
    I have a home with load-bearing clay brick basement walls that is constructed withe three wythes: the two on the outside abut each other and the third inside wythe follows a 1.5" air gap. All three are held together with tie bricks. Question: Does the air gap mean that the inside wythe is "warm" and the outer two are "cold". After following along with this article and the many comments, the temperature of the wall seems to be key in determining what materials can be placed directly against the brick.

  56. User avater GBA Editor
    Martin Holladay | | #56

    Response to Rich Steenwyk
    Rich,
    Q. "Does the air gap mean that the inside wythe is 'warm' and the outer two are 'cold'?"

    A. During the winter, the innermost whythe of a multi-wythe brick wall will always be warmer than the outermost whythe, regardless of whether the wall has an air gap.

    The air gap will provide some R-value, of course, especially if air leakage through the wall has been controlled (and you probably can't make that assumption). Under ideal circumstances, the R-value of the air gap probably falls in the range of R-1 to R-2.

    In winter, the temperature of the bricks will be colder on the exterior of the wall than on the interior of the wall; and will be colder near the top of the wall than near the bottom of the wall.

    No portion of this wall can be considered well insulated.

    Most building experts would probably note that, in most circumstances and in most climates, it's probably safe to install 2 inches of closed-cell spray polyurethane foam on the interior of this basement wall. However, the rigid foam will lower the wall's drying potential, and this change can lead to an increase in the moisture content of the sill beam resting on the brick wall. If the above-grade portion of the wall is relatively high (more than 8 inches), and is well ventilated (exposed to sunshine and not shaded by vegetation), the risk of rotting your sill beams is lowered. If conditions indicate that your sill is at risk, it may be advisable to jack up the house about 1/2 inch so that you can insert a capillary break (metal flashing or rubber roofing) between the top of the brick wall and the sill beam.

    Here is a link to a relevant article that deals with stone foundation walls (rather than brick foundation walls): . While the walls discussed in this article differ from yours, some of the advice in the article is still relevant to your case.

  57. Edward Lampe | | #57

    Philly rowhouse needs to be insulated
    Now my head is spinning enough to lift right off of my body.

    All that I want to do is reduce my heating and cooling loads. It seemed simple...insulate. But then there's vapor control and condensation and now brick concerns.

    Let me see if I understand; cellulose is out, fiberglass is out, spray foam may be ok, vapor barrier is out, vapor permeable is ok, foam boards may be ok, air movement is bad, fluid applied permeable membranes may be necessary.
    Some or all of what I just said may be partly or completely right or wrong. That's where I'm at.

    There is a parapet wall 3' high in the front of the house that appears to have suffered no damage in 70 years.

    This house is a rowhouse. Just the 19' wide front and back walls are exposed. It's 70yo (1945) and has a block and brick interior wythe and a brick face. The walls were furred with 3/4 stock and then covered in plasterboard and plaster.

    The plaster and plasterboard are fully stripped as is the ceiling below the flat roof. I was going to 2x4 stud the walls and insulate with Roxul or fiberglass but now I'm not sure what to do. How do I get a definitive answer specific to my house and climate?

    Ed

  58. User avater GBA Editor
    Martin Holladay | | #58

    Response to Edward Lampe
    Edward,
    Q. "I was going to 2x4 stud the walls and insulate with Roxul or fiberglass but now I'm not sure what to do."

    A. My article is fairly clear on this point: you don't want to insulate this type of building with an air-permeable insulation like Roxul or fiberglass.

    Q. "How do I get a definitive answer specific to my house and climate?"

    A. I suggest that you take the advice provided in my article. If you don't have the confidence to reach any conclusions based on the recommendations in my article and a thorough inspection of the building, you should invest a few thousand dollars and hire a consultant from the Buildling Science Corporation to help you. The investment in consulting fees will be less than the cost of repairing your building if you make a major insulation error.

  59. Edward Lampe | | #59

    Philly rowhouse II
    Thank you for your reply.

    I've taken the time to do reread your article and others like it.
    I have looked over the brickwork and feel secure that it is robust and unlikely to suffer a freeze-thaw issue. The 3' tall parapet wall appears identical to all other brickwork.

    If I have concluded correctly, good insulation practices would be either closed cell spray foam applied directly to the inside of the masonry wall with a less expensive infill, a flash and batt approach.
    Or, coating the wall with a fluid WRB and then adhering rigid foam board, polyiso, on top of that. The wall is wavy by up to 1/2" so the flash and batt seems ideal.
    And for both, positioning the studs off of the masonry wall as much as is feasible and creating a well executed air barrier.

    My question now is, for a flash and batt, what is the minimum thickness for the flash as far as both reducing the chance of condensation on the flash and providing proper vapor permeance? I know I read it somewhere amongst all of my research but now can't locate it.
    And would the batt be faced or unfaced?

    Thanks again, this article has prevented me from making a serious and costly mistake.

    Ed

  60. User avater GBA Editor
    Martin Holladay | | #60

    Response to Edward Lampe
    Edward,
    Once again, I'm going to stick with the advice in my article. Your attempt to come up with new approaches is risky.

    If you have determined that your bricks are suitable for insulation on the interior, you can install between 2 and 3 inches of closed-cell spray foam against the bricks.

    I do not recommend that you install a water-resistive barrier on the interior side of your bricks.

    I do not recommend that you try to insulate your bricks with rigid foam.

    I do not recommend that you attempt a flash-and-batt insulation job.

  61. J. Sip | | #61

    Philly RowHouse manual and insulation
    Hi,
    My home is a 1909 Philly row home with brick construction. My walls appear to be an inside run of cement brick with more expensive traditional brick for the exterior run. There appeared to be some settling, but no mortar problems or crumbling bricks.
    I'm in the middle of a kitchen remodel which is the back end of the row home. The room has two exterior walls. The whole room was gutted.
    Your site suggests that Philly is ok in terms of freeze thaw. One of my walls is protected by a cantilevered second floor from rain, the other looks onto my neighbors wall with a span of about 8 feet, so some rain exposure, but not terrible and really wind dependent.

    Philly has a RowHouse Manual. They suggest keeping an air space between the interior of the brick and the insulation, then a vapor barrier attached to the studs between studs and drywall. If their recommendations are correct, this will lend itself perfectly to foam boards.

    Can you offer your perspective on Philadelphia's advice?

  62. James Brown | | #62

    blown fiberglass
    I understand fiberglass can be blown in to achieve a higher density and lower air permeability rate than cellulose. Wouldn't this make it a less risky alternative to cellulose?

  63. User avater GBA Editor
    Martin Holladay | | #63

    Response to James Brown
    James,
    It's hard to generalize about the density and air-permeability of blown-in insulations. Either cellulose or fiberglass can be installed at a high density or a low density; much depends on the skill of the installer.

    Cellulose and fiberglass behave differently. Cellulose is hygroscopic, while fiberglass is hydrophobic. In other words, cellulose does a better job than fiberglass of redistributing moisture from one damp location. Because of this, it's dangerous to assume that fiberglass will behave the same as cellulose.

    This article describes the use of cellulose by Chris Benedict to insulate old brick buildings in New York City. The technique makes some experts nervous; in general, spray foam is probably less risky. If you want to experiment with blown-in fiberglass for this application, you are entering unknown territory. Considering the consequences of failure, I don't advise experimentation.

  64. User avater GBA Editor
    Martin Holladay | | #64

    Response to J. Sip (Comment #61)
    J. Sip,
    You wrote, "Philly has a RowHouse Manual. They suggest keeping an air space between the interior of the brick and the insulation, then a vapor barrier attached to the studs between studs and drywall. If their recommendations are correct, this will lend itself perfectly to foam boards. Can you offer your perspective on Philadelphia's advice?"

    I'm going to stick with the recommendations given in this article, even for Philadelphia. If you leave an air space between the interior of the brick and the insulation, you can have convective loops that lower the effectiveness of the insulation. Moreover, interior vapor barriers (presumably, the manual is recommending polyethylene) can cause problems, especially in air conditioned buildings.

  65. Mike S | | #65

    Another Old Philly Row -
    Martin,

    Thanks for all the great info. I'm wondering what you think about the pictures of the major renovation we will be undertaking on a Circa 1900 house in Philadelphia. House is mid-row so only the front and back along with a breezeway of ~1200 SF are exposed. I will be keeping the original front facade so the plan there will be to do 3" of closed cell spray. The sides and back are currently stucco over brick.

    Will applying EIFS be possible without first repairing and cleaning the entire stucco surface? Is 4" of EIFS possible to get the required R- value in Philly?

    Does EIFS make more sense then just doing rigid foam with another cladding like hardie board?

    Is there an argument to re-coat the existing stucco with additional cement based stucco and just do spray foam on the interior for the purpose strengthening the wall assembly?

    Thanks

  66. Roman Stankus | | #66

    Hot-humid climate walls
    Martin, I'm looking at insulating a circa 1900 single story building with 12" brick bearing walls and flat roof. A recent Building Science Corp. article on insulating brick bearing walls says that insulating on the interior with cellulose if OK in a hot/humid climate - brick should have a fluid applied >10 perm air/water barrier coating on the inside face of the brick. Can you suggest some readily available products that fit the bill? Are any of them products that could be installed by a DIY'er? Roller application? What would you recommend if there is an intact/sound interior plaster finish directly applied to the brick? Can the plaster stay? In the BSC article - it also suggests installing an exterior polymer cement parging on the exterior of the brick (or stucco). Do you have any products/manufacturers for the polymer coating? Location is South Georgia. Thanks.

  67. User avater GBA Editor
    Martin Holladay | | #67

    Response to Mike S (Comment #65)
    Mike,
    The best person to answer most of your questions is an EIFS contractor. If you can find an EIFS contractor to do the work you want and stand behind it, you are all set.

    How thick should the insulation be for an EIFS job on a retrofit? That depends on your local code -- most codes don't have minimum R-values for retrofit work -- your budget, and the physical limitations of the EIFS system that your contractor uses.

    If you can't find an EIFS contractor that you feel comfortable with, the other option -- exterior foam, furring strips, and fiber-cement siding -- is also possible. As with any construction decision, you have to weigh the costs and the hassle factor with the advantages and disadvantages of each approach.

  68. User avater GBA Editor
    Martin Holladay | | #68

    Response to Roman Stankus (Comment #66)
    Roman,
    Q. "The brick should have a fluid applied >10 perm air/water barrier coating on the inside face of the brick. Can you suggest some readily available products that fit the bill?"

    A. Products include StoGuard, W. R. Grace's Perm-A-Barrier VP, Henry Company's Air Bloc 31, DuPont's Fluid Applied WB System, and Tremco's Enviro-Dri. For more information on these products, see Housewrap in a Can: Liquid-Applied WRBs.

    Q. "Are any of them products that could be installed by a DIY'er? Roller application?"

    A. Yes and yes. Talk to the manufacturer of the product you want to use before proceeding.

    Q. "Can the plaster stay?"

    A. Probably not, but I'm not an expert on these products. Again, talk to a technical representative for the product you are considering.

    Q. "Do you have any products/manufacturers for the polymer coating?"

    A. No, I'm afraid not. You'll have to start with some online research.

  69. M H | | #69

    does a painted exterior make a difference
    I have a residential home built in '17, double wythe exterior walls that i want to insulate. The plan so far is to fur out all exterior walls with stick framing. Plan to foam the floor joist in the vented attic, exterior walls and attic.
    The plan also includes painting the home, my question is if the exterior of the home is painted does this eliminate the concern about freeze/thaw?

  70. User avater GBA Editor
    Martin Holladay | | #70

    Response to Mark Herndon
    Q. "If the exterior of the home is painted, does this eliminate the concern about freeze/thaw?"

    A. No.

    First of all, paint is temporary, so it can't be depended on as a long-term protection against a threat that is capable of destroying your building.

    Second, most brick experts advise against the use of exterior paint or coatings, because paint and coatings interfere with the ability of damp bricks to dry to the exterior.

    Finally, you didn't tell us your climate zone, so it's hard to provide advice.

  71. M H | | #71

    4A
    The exterior has been painted before, thus the exterior paint question. I understand it is not a long term solution, but if this home is to be insulated with closed cell, will repainting and maintaining the exterior address some of those concerns?

    I also understand I may be concerned over something i dont need to be if this freeze/thaw issue is not going to affect my home in TN.

  72. User avater GBA Editor
    Martin Holladay | | #72

    Response to Mark Herndon
    Mark,
    In your climate, your plan will work. Closed-cell spray foam is a good way to insulate this type of house, and your climate is mild enough that you don't have to worry about freeze/thaw damage.

    If I were you, I would let the old paint flake off so you could see the real bricks underneath. But I don't think it matters one way or another whether a brick house in your climate has paint -- except that you will be faced with a regular maintenance headache due to the need for periodic repainting.

  73. Bob Fortune | | #73

    Never make a mistake to
    Never make a mistake to underestimate the nature of brick differing in quality. Not all of them would behave in a similar fashion. Don’t take a chance if you have some precious structure at stake. No doubt about it, a professional would take the responsibility and they also have appropriate equipments, tools and tests to figure out good bricks from bad.

  74. John Semple | | #74

    Save the bricks and timbers, then worry about insulation
    I just purchased an antique brick cape located in central Vermont. It has survived in good condition for at least 150 years with 2-wythe brick exterior walls and a thin layer of plaster/mortar for insulation. There are 24’ wood timbers that connect the brick walls. They appear to be in good shape, too.

    Is there some minimalist approach we can take to insulate the brick exterior walls so that we stop some of the heat loss without endangering the bricks and timbers? We were planning to add interior studs and drywall. Would that air space, without any insulation, stop some heat loss without endangering the bricks and timbers? Would 1” of spray foam applied to the interior bricks be thin enough to avoid any negative consequences?

    I’m not so worried about minimizing my heating bills as I am about ruining my antique bricks (or damaging the timbers). I will address any drainage issues come spring, but the house is being renovated now.

  75. User avater GBA Editor
    Martin Holladay | | #75

    Response to John Semple
    John,
    The answers to your questions can be found in my article. Adding interior insulation will make the bricks colder and wetter than they would otherwise be, raising the possibility of damage. To assess the risk, you have to assess the quality of the bricks and their exposure to exterior moisture. When in doubt, hire an experienced consultant to help you.

    Adding exterior insulation is far less risky, of course.

  76. Meyer Brendan | | #76

    Type of mortar is critical to performance
    Since adding exterior insulation might not be allowed by local preservation codes, thus making interior insulation the only option, it should be considered that the material of the mortar or the presence of inappropriate cement mortar repairs is an important distinction relevant to this question.

    In historic buildings, mortar in a brick wall assembly is the sacrificial material. It makes up about 20% of the surface area of the wall. A lime based mortar has an absorptive property that allows it to pull liquid out of masonry units. Absorbed water in the mortar will evaporate. Absorbed water in historic mortar triggers a self-healing process where water dissolves calcium in the binder and transports it to voids thereby healing microscopic cracks. After about 75 years, lime based mortar degrades to the point that it needs to be repointed with new mortar. The mortar fulfills its role as the sacrificial material in the wall assembly.

    Modern cement based mortars do not absorb water or self heal like lime based mortars. Cement mortars are more resilient than historic brick. Historic brick repointed with modern cement mortars retains more water, is subject to greater stresses from freeze/thaw cycles and becomes the sacrificial material. Instead of replacing mortar every lifetime, bricks have to be replaced instead.

    Adding interior insulation to a historic brick wall repointed with cement mortar will be more likely to spall brick than adding interior insulation to a historic brick wall repointed with lime based mortar.

  77. Michael Jordan | | #77

    Unusual brick house
    I am hoping to revive this old article. I have a brick house from 1852 but it is a timber framed building with a brick exterior skin and brick nogging between the timber framing. I am not sure how the skin is attached to the building or if the courses of exterior brick are somehow attached to the nogging. The interior walls were originally either plaster and lathe or tongue and groove panelling, I think. That's all gone now and has been replaced with drywall before I bought the place. Has anyone every seen construction like this? I wonder if the insulation concepts in this article would apply to my house.

  78. User avater GBA Editor
    Martin Holladay | | #78

    Response to Michael Jordan
    Michael,
    From your description, I would say that the principles discussed in this article apply to your building.

  79. Jason Holstine | | #79

    Why not rigid foam
    Martin, I'm not clear why you don't believe rigid foam on the interior side of above grade brick is acceptable? Is it because it won't form to the brick pattern, thus leaving air/water channels?

    FWIW, this is for the DC/MD region, all above grade buildings, typically vintage 1895-1950.
    We'd like to avoid framing out walls to minimize floorspace intrusion. Understanding that it's not ideal, our thinking is continuous ~R8 insulation, air sealing and improving flashing is still a significant improvement. Thanks.

  80. User avater GBA Editor
    Martin Holladay | | #80

    Responser to Jason Holstine
    Jason,
    Q. "Is it because it won't form to the brick pattern, thus leaving air/water channels?"

    A. Yes.

    Your climate is relatively mild, so the risk of freeze/thaw damage is low. The use of rigid foam in your climate may work, especially if the perimeter of each piece of rigid foam is carefully air-sealed with canned spray foam. It's your building; you have to assess the risk/benefit equation. Closed-cell spray foam would be a better choice.

  81. Ryan Ch | | #81

    some recent work by a British
    some recent work by a British preservation agency suggests that ivy in the proper circumstances actually protects brick, by mitigating freeze thaw cycles. The surface temperature of brick behind ivy remained far more constant. They had specific recommendations for how to tuckpoint to discourage rootlet penetration.

    I can't find the article at this point, but wonder if anyone had seen it, had any thoughts on this, or would care to venture whether American climate zones might be so distinct as to make the study unuseful in this hemisphere?

  82. User avater GBA Editor
    Martin Holladay | | #82

    Response to Ryan
    Ryan,
    I'd be interested in reading the paper if anyone has a link.

    Two comments: In cold climates, ivy loses its leaves in winter, so it's hard to imagine that it can provide much of an insulating blanket -- especially when the temperature drops to 0°F. So I'm guessing that research based on British ivy during British winters probably won't apply to the colder areas of the U.S.

    .

  83. Ryan Wilson | | #83

    response to Martin on ivy
    For some reason, the spam filter blocked my answer, probably because it had links. Bottom line is that if you use a search engine for english heritage ivy and brick, you'll find the report I was talking about. Though once I rediscovered it, I skimmed it and noticed that more of the research was on limestone walls than on brick.

    The other thing is that if you search for english ivy united states climate zone, you'll find pages that suggest english ivy is evergreen through most of the US. I live in Chicago, and English ivy should be evergreen here.

  84. User avater GBA Editor
    Martin Holladay | | #84

    Here are some links
    Ivy links:

    A news story:

    The paper: .

    A relevant excerpt from the paper: "Looking in more detail at the differences in the aspect, degree of exposure and thickness of ivy cover at each site helps to explain some of the variation in strength of the ‘thermal blanketing’ effect of ivy. The wall studied at Worcester College, Oxford is south facing with high exposure to light throughout most of the day (no nearby shading) and has a relatively thick cover of ivy (c. 45 cm). The thick ivy here has been proved to provide an excellent way of reducing excessive heating under these conditions. In contrast, the wall studied at the Abbey Inn, Byland has a relatively thin cover of ivy (c. 20cm), is east facing and exposed tohigh levels of light (no local shading) and in an area prone to very cold winter conditions. Even this thin cover of ivy has been proven to prevent extremes of cooling in this cold climate – and prevented freezing within the winter months (see Chapter 4, Figure 4). Smaller, but significant, impacts on diurnal temperature cycling were recorded at the south-facing Ramsey site, which has some shading from nearby walls and trees and a thin (c 24 cm) cover of ivy. Even the very thin and patchy cover of ivy at the Nailsea site (< 10cm thick) has been demonstrated to have a significant effect on daily temperature cycling at a west-facing site which is quite heavily shaded all round by other trees. The other sites studied within Oxford showed similar trends."

  85. Sharon Slovenec | | #85

    New construction window installation
    We've gutted the plaster and lathe in the kitchen and the back bedroom we're converting to a bathroom in our 2-wythe brick row house in Pittsburgh. We'll most likely insulate with 3" of closed cell spray foam with the studs held out 1" from the wall per your recommendation.

    However, we're uncertain about the window installation. Should we use masonry clips, install new PT bucking and use a nailing flange or use some other method?

    We're replacing original double hung windows with weight pockets. So, the interior M.O. is several inches larger on each side than the M.O. on the outside edge of the outer wythe.

    I'd appreciate any references to detailed measures or methods for lining and framing around the M.O. and installation.

    Most of the contractors I've spoken to so far don't believe in using spray foam on windows or in the need for pan flashing. So, I'm still searching for someone who believes air sealing and providing a draining plane are as important as I do.

    Thank you for your time and consideration.

  86. User avater GBA Editor
    Martin Holladay | | #86

    Response to Sharon Slovenec
    Sharon,
    You should start by watching GBA's 4-part video series on replacing a window in a brick house. Here is the link to Video #1 in the series: Video: Replacement Window in an Old Brick House (1 of 4).

    The video shows the use of an insert replacement window. If you have no remaining frame in your opening, you would instead buy a new flangeless window, and you would follow the installation instructions provided by the window manufacturer. (Window manufacturers sell windows designed to be installed in brick buildings.)

  87. Claudia Fader | | #87

    dimpel board with spray foam
    We are currently renovating a 130 year old solid brick building (double wythe) in Toronto and had originally planned to use 2" of 2 lb closed cell spray foam sprayed to interior of brick walls with 2x4" framing located 1" off the wall so that we can spray between studs and brick walls.
    After we had started with the renovation the scope got extended quite a bit. We had to replace some of the bricks and repointed some areas using lime mortar. We are going to replace all eaves, downspouts and flashing, ensuring that we will have proper drip edges and water management everywhere. So far all this seems to be in line with your recommendation on how to insulate old buildings.
    However after having read an article from Dr. Kim Pressnail (refer to link below) we consider providing an air space between the brick wall and the spray foam insulation to avoid damage caused by moisture trapped in the inner layer of the brick.
    We would like to entertain the idea of using dimple board to create the air space. Staple dimple board on to the brick wall, have the 2x4" framing 1" offset and install spray foam onto the dimple board and in space between studs and dimple board. How do you feel about this approach?

    https://lakesideca.info/sites/default/files/Solid%20Masonry%20Interior%20Insulation_retrofit%20w-drainage%20mat.pdf

  88. User avater GBA Editor
    Martin Holladay | | #88

    Response to Claudia Fader
    Claudia,
    I think that you should stick to Plan A -- without the dimple board.

    I am aware of Dr. Pressnail's work; I have heard him speak and have written an article about his research. Here is a link to the article: Nuggets From the 2013 Westford Symposium. (Scroll down to the bold heading that reads, "Insulating old buildings with structural brick walls.")

    I think that a fair characterization of Pressnail's work is to call it experimental. Pressnail is still at the data collection and assessment phase. Until Pressnail knows more, and confirms the validity of his approach, it's best to stick with a tried-and-true approach.

    Pressnail's method depends on drilling ventilation holes through the brick. There is always a risk of condensation problems when you have an air space adjacent to cold bricks.

  89. Timothy Lawlor | | #89

    Purchasing an Old Brick Home in Vermont
    We are considering purchasing an old brick home in Vermont, built in 1826. The current owners have updated it with insulation and spray foam in the basement. Would anyone know of a good home inspector in Vermont who specializes in inspecting brick homes and is well versed in these insulation matters?

  90. User avater GBA Editor
    Martin Holladay | | #90

    Response to Timothy Lawlor
    Timothy,
    You can't beat the consultants at the Building Science Corporation. Here's the contact info:

    Building Science Corporation
    70 Main St.
    Westford, MA 01886
    978-589-5100

    Their consultants travel frequently, to locations across the U.S. and Canada. Vermont would be considered close.

  91. Timothy Lawlor | | #91

    BSC Contact
    Thanks very much for the information, Martin. I will contact them soonest.

  92. Jon R | | #92

    See below for a case where
    See below for a case where spalling was occurring and it stopped with better air sealing and negative building pressure.

    Google: 2075-5309/2/4/534/pdf

  93. abcc | | #93

    Leaving air gap with rigid insulation?
    Hi Martin,
    Super informative article! Hope it's still open for discussion...

    We have walls of double and triple wythe exterior loading-bearing brick wall in New York City, a fully detached brick house. We removed the plaster and lath which were attached to 3/4" thick strips of wood nailed directly to the brick.
    What do you think of attaching 2" rigid foam board to the wood strips, leaving a 3/4" air gap between foam board and the brick? I figure this air gap was part of the original design and its worked for 100 years. This would seem to allow the brick to keep 3/4" air gap to still "breathe" since the insulation would not be mounted directly on it. What do you think of this approach? An architect suggested filling in between those wood strips with 3/4" thick rigid foam too, but we were wondering if leaving it empty would help let things "breathe" as it was designed.
    We know you advise spray foam in the best option for insulating exterior brick (if you can't insulate the outside of the wall), but we just can't afford the spray foam cost.
    Please let us know what you think- thank you again for sharing such a helpful article!
    AJ

  94. User avater GBA Editor
    Martin Holladay | | #94

    Response to AJ (Comment #93)
    AJ,
    Q. "What do you think of attaching 2 inch rigid foam board to the wood strips, leaving a 3/4 inch air gap between foam board and the brick?"

    A. I stand by the advice given in my article -- namely, to use closed-cell spray foam, but only if the site assessment for moisture issues and the assessement of brick quality are encouraging.

    The problem with your suggested method is that the rigid foam insulation will make the interior surface of the bricks much colder than previously. Now that the interior face of the brickwork is cold, the surface will be susceptible to condensation or even frost formation. If you leave an air gap, you leave open the possibility that air currents will carry warm, moist interior air into contact with the cold bricks.

    You don't want that type of condensation. That's why you need closed-cell spray foam -- to preclude the possibility of air movement in this critical area.

  95. abcc | | #95

    One more thought...
    Thanks for the quick reply, Martin.
    I definitely get the preferred option is spray foam and we wish we could afford that.
    But the cost won't allow, so if spray foam wasn't an option, would you stick rigid foam right onto the brick or leave the 3/4" air gap?
    I.e. what's your next favorite option?
    And yes, I know you may not like both options, but just imagine spray foam wasn't invented yet :)
    Thank you!

  96. User avater GBA Editor
    Martin Holladay | | #96

    Second response to AJ
    AJ,
    As my article points out, the consequences of bad details in this case are quite serious: your building can start deteriorating, and can literally begin falling apart.

    You're not going to get me to alter my advice, I'm afraid.

  97. abcc | | #97

    Advice received!
    Last question: does the situation change any if the exterior of the brick is covered in stucco already?
    We just have one 40' long wall that was stucco'ed over the brick outside so wondering if this wall can be treated any differently to avoid using spray foam.

  98. User avater GBA Editor
    Martin Holladay | | #98

    Third response to AJ
    AJ,
    I don't have enough experience with stucco over brick in cold climates to answer your question. But I'll provide general advice to GBA readers in your position: If you are willing to consider the application of exterior stucco, by far the best solution to your problem is to install exterior insulation between the bricks and the stucco.

    When this approach is taken with synthetic stucco, it is called EIFS (exterior insulation and finish system). It's too bad that you didn't call up an EIFS contractor instead of a stucco contractor.

    Exterior insulation is always preferable to interior insulation for this type of building.

  99. patrickmay | | #99

    Correcting poor insulation construction in a double wythe home
    Martin,

    Thank you for writing such a thorough article. I am a first time homeowner of a double wythe brick home in Washington DC. The home was built in 1900 and extensively renovated by a company that sold me the house in 2016. The house was gutted down to the point of them installing new joists.

    Due to some issues that I have noticed, I am seriously concerned that parts of the renovation were not done correctly. First, they constructed the interior walls with a furring strip adhered to the brick, followed by 1/2 inch foam board, a layer of a plastic vapor barrier, then drywall. There is no air gap. As a result, in the hot humid period of the year, water condenses on the vapor barrier and runs down the inside of the walls. I discovered this issue when water leaked out of an outlet and I cut open a section of the wall to investigate. In addition to threatening the integrity of the building, I am worried it poses a serious fire hazard to have outlets exposed to water in this way. As far as I can tell, this issue only occurs on one side of the house, which faces an alley way and is fully exposed to the elements. I think this is because this exposure results in the largest temperature differential between the inside and outside.

    The house is painted, and there is some paint cracking and there is limited spalling.

    At this point I am seeking confirmation that this was the incorrect way for the house to be insulated. I think that there is a long path forward for me that includes get an expert to assess the exterior brick as well as getting someone to rip down the drywall and insulation on at least the wall that is experiencing the problems, letting the wall dry out, and then reinsulating and installing drywall.

    I would love any input or advice you can provide.

    Thanks,
    Patrick

  100. User avater
    Dana Dorsett | | #100

    need clarification
    If I understand the stackup correctly you have:

    great outdoors | double wythe brick | furring + air | 0.5" foam | polyethylene sheeting | drywall ???

    If yes, you must have about 1.75" between the interior paint and the brick, and shallow 1.25-1.5" deep electrical boxes(?)

    [Editor's note: This thread has additional comments on Page 3. Click the number 3 below to continue reading.]

  101. User avater GBA Editor
    Martin Holladay | | #101

    Response to Patrick May (Comment #99)
    Patrick,
    Your walls are probably experiencing inward solar vapor drive. For more on this phenomenon, see this article: "When Sunshine Drives Moisture Into Walls."

    If my guess is correct, that means that the wall with the problem is not facing north.

    I agree with your analysis: This wall was not insulated correctly.

  102. patrickmay | | #102

    Correcting poor insulation construction in a double wythe home
    Martin,

    The wall is north east facing, so doesn't see constant sun throughout the day, but I think the combination of high ambient heat, some direct sunlight, and high humidity all contribute to it being enough heat and moisture to cause a problem. The description of solar vapor drive in the article you linked seems exactly like what I am experiencing. I think a variety of factors including shading from neighboring buildings and a thicker front to the house have kept the issue from presenting problems in other areas. Regardless, in addressing it I suppose we will need to cut holes at the base of all of the walls and inspect for condensation. Worst case scenario, we would have to replace all drywall on all exterior facing walls, which is a daunting and expensive task.

    I will have to get an expert to come and look at it themselves to confirm our suspicions. I wonder if I would have legal recourse like the home owners who bought houses from Zaring Homes and then had to have them retrofitted?

    Thanks again for writing the article and taking the time to respond!

    Patrick

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