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Updating a Massachusetts Colonial

A homeowner weighs the benefits of sealing air leaks and adding insulation in the attic and the basement

Posted on Mar 5 2018 by Scott Gibson

In coastal Massachusetts, Justin Brown is looking for ways to upgrade the energy performance of his very old house. It sounds as if previous owners had taken some steps to tighten up the building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials., but they didn't go far enough with either air sealing or insulation. Now, Brown wants to complete the job.

One area of particular concern is the attic. It's insulated with a mix of fiberglass and cellulose, he writes in a Q&A post, but a cold snap this winter produced some frost on the underside of the roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. .

Completing the insulation of the foundation walls also is on Brown's to-do list (see the floor plan and images below). The foundation is a mix of poured concrete and fieldstone, and while Brown has added 3 inches of rigid insulation to the concrete foundation walls, the fieldstone walls remain to be done.

"I spent hours digging through cellulose and air sealed some wall plates and open wall cavities that the previous homeowner's air-sealing and insulation contractors clearly missed," Brown writes. "There is one 30-foot exterior wall plate in the eaves I cannot reach to air seal from inside the attic."

The 10 recessed lights in the attic floor have been upgraded with LED airtight retrofits, but are not covered with any insulation. In the basement, the rim joists have been insulated with 2-inch extruded polystyrene and spray foam. But the inside of the foundation walls, a mix of poured concrete and fieldstone, have not been insulated.

Brown has found an ally in his efforts to upgrade. Technicians from , a utility energy efficiency program, have visited the house and are offering to remove the existing attic insulation, seal any air leaks that have been overlooked, and add insulation to bring the entire attic up to R-49. After a 75% rebate, Brown would pay $500.

"Is it worth pulling the exterior soffit/fascia board to seal that 30-foot exterior wall plate?" Brown asks. "I have a hard time quantifying how much air loss that will stop. Mass Save says they won't do that; it would be up to me.

"I know quantifying [return on investment] is tough, but will I see substantial benefits going from R-30 to R-49 and really burying the recessed lights in cellulose?" he continues. "I was estimating about a 5-year payback."

That's the topic for this Q&A Spotlight.

Mass Save's offer is a “bargain”

GBAGreenBuildingAdvisor.com editor Martin Holladay urges Brown to jump on the Mass Save offer for attic improvements.

"The air-sealing work being offered by Mass Save (for just $500) is absolutely worth the money," he says, "and the upgrade from R-30 to R-49 is being thrown in for the same price. So do it! It's a bargain."

The case for pulling the soffit and fascia to allow access for more air-sealing work is less compelling. "There is no easy way to estimate the value of pulling the soffit and fascia to gain access to the area for air sealing," Holladay writes. "Do it if you can afford the cost — skip it if you can't."

David Baerg suggests that sealing air leaks in the attic is crucial if Brown wants to avoid moisture problems in the future. "If you have enough air leakage to cause moisture problems in cold weather, insulating without air sealing will make the problem worse," he says. "The attic will be colder and, therefore more condensation will occur."

Brown now uses about 450 gallons of fuel oil a year for heat and hot water. Baerg doubts that Brown will see a five-year payback by increasing attic insulation from R-30 to R-49.

"That upgrade is marginally worth it where I work (northern Ontario — much colder with higher fuel prices)," he says. "Do it to make your house more comfortable and reduce ice dams, and expect a 3%-5% reduction in your oil bills."

Are the can lights a problem?

Recessed lights are a well-known source of air leaks, Baerg adds, and even the sealed LED fixtures Brown mentions may not be as tight as they seem.

"Did you have a blower door test done?" he asks. "Did your advisor find significant leakage at the recessed fixtures? Even if they are ‘airtight’ they can still be improved. There is likely leakage through the wire channel — caulk this from the attic. And the seams in the can likely leak a bit — seal them with aluminum foil duct tape. And, of course, put a bead of caulking between the can and the ceiling from below."

The recessed light retrofits are gasketed, Brown replies, and seem tight to the ceiling. But he wonders whether it would be a good idea to build airtight boxes out of 1-inch rigid insulation and cap the fixtures in the attic before any additional cellulose is blown in.

"Installing LED retrofit kits with gaskets cuts down on air flow through a recessed can, but doesn't stop the air flow completely," Holladay says. "If I were making the decision, I would retrofit some type of airtight cap over each recessed can.

"But it's fussy work," he continues, "and the decision depends in part on how many recessed cans you have to address, how easy or difficult the access is, and who's doing the work (and at what cost)."

Holladay suggests using foil-faced polyisocyanurate because it's easy to tape.

Work in the basement

The basement insulation question boils down to this: Will Brown be wasting his money if he adds rigid insulation to 70% of the walls while leaving the remaining 30% uninsulated? That's what the technicians from Mass Save tell him, but Baerg is among those who disagree.

Go ahead and insulate the poured concrete foundation walls, he advises, and Dana Dorsett is quick to agree.

"Heat loss is a U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. times area type of thing," he says. "It's definitely not a waste of time to fix 70% of the total area.

"Only 2 inches of polyiso won't get you to Massachusetts code minimum (= R-15 continuous insulation)," Dorsett adds, "but it's still way better than nothing. Depending on how much above-grade exposure you have on the foundation, the basement losses (even at cooler basement temperatures) can be 20% or more of the heat loss. Fixing 70% of that with even R-12 (2 inches of polyiso) would result in more than a 10% reduction in overall fuel use, even if the 30% of the basement that's fieldstone is left uninsulated."

And if he does go ahead with insulating the fieldstone foundation walls, Holladay adds, closed-cell spray polyurethane foam would be the best route. "Not cheap," he says, "but effective."

For the fieldstone portion of the foundation, Dorsett suggests 1 inch of closed-cell foam followed by blown insulation in a 2x3 stud wall. That, he says, would get Brown to the code-minimum requirement for basement insulation in a Climate Zone 5A location. But using cellulose in that application could be risky, he says, because in the event of even a minor flood the cellulose would draw up any bulk water "like a sponge and take forever to dry." Blown-in fiberglass wouldn't have that problem.

One last note, Dorsett says: Adding between 2 1/2 inches and 3 inches of polyiso on the concrete portion of the foundation rather than the 2 inches Brown has in mind would help him meet code code requirements. might be a good source of reclaimed insulation, Dorsett says.

Insulation and moisture control

There is one wrinkle in the insulation picture in Brown's basement. He writes that the outside of the basement walls are insulated with what appears to be 2 inches of polystyrene (either extruded or expanded), leaving 2 or 3 feet of foundation above grade.

How does this affect the ability of the concrete to shed moisture, especially in light of his plans to add additional insulation on the interior?

Dorsett offers this assessment: "If the exterior polystyrene insulation is only below grade, it has only minimal affect on the drying capacity of the foundation, but it does limit the rate that ground moisture can reach the walls, and raises the temperature of the concrete, helping it dry toward the interior."

Brown plans to end the interior insulation 1 foot above the basement floor to make absolutely sure that it doesn't wick up any moisture. If he does that, Dorsett says, moisture wicking up from the footing will be able to dry reasonably well to the interior.

But a 1-foot gap is too much, Holladay tells him. "If you are worried that moisture might wick up the polyiso, you can stop the polyiso 1 inch off the floor," he says. "But 1 foot is too much -— it just means that your wall isn't fully insulated."

Our expert's opinion

Peter Yost, GBA's technical director, added these thoughts:

We often follow up with folks whose posts lead to these Q&A Spotlights. We're looking for additional information about their projects so we can make the response at the end of the blog as helpful as possible. But boy, did we hit gold with Justin Brown!

Justin not only provided a ton of useful photos (see photo gallery), but he also drew up a foundation plan to orient us and has responded in detail to a host of follow-up questions that I posed.

Here is what we have learned, and then suggested:

Blower door test: Justin did have a blower door test done early on in his work on the house, but it was more a part of a sales pitch than a bona-fide test. He is certainly open to having one done now. A blower door test would help with two concerns: how much air leakage is taking place at the eaves; and how airtight is the 6-mil polyethylene installed in the highly irregular areas of his fieldstone crawlspace. So when this test is done, it’s important that the test be used to quantify airtightness but also to identify locations of air leakage. It would be great to get it done soon with good indoor-outdoor delta T and add in infrared imaging during the blower door test.

Ice dams: I asked Justin about ice dams because if heat loss (conductive and convective) at the eaves is resulting in ice damming, then dealing with the eaves becomes more important. Justin let us know that while the previous owners reported some problems, he has not noted any but agreed that keeping his eye on this is important as he finalizes his work plan on the house.

Complete the gutters: It’s particularly important to move the roof runoff away from the fieldstone foundation, and it looks as though on the front of the house the gutter and downspout does just that. A gutter on the front porch, particularly on the end adjacent to the fieldstone foundation, is important to add.

Install kick-out flashings: There appears to be more than one shed-roof-meets-sidewall location where kick-out flashings are needed, particularly at the left hand end of the front porch adjacent to the fieldstone foundation section.

RadonColorless, odorless, short-lived radioactive gas that can seep into homes and result in lung cancer risk. Radon and its decay products emit cancer-causing alpha, beta, and gamma particles. testing: Justin has used more than one radon kit (probably the alpha-tracker type, the most reliable), conducted in late summer and early spring, which showed 8 pCi/LAbbreviated pCi/L, this term refers to the relative radioactivity contributed by radon gas to one liter (1,000 cc's) of air. A picocurie is one-millionth of a curie and represents about 2 radioactive particle disintegrations per minute. EPA has established an action limit (the level at which some form of radon mitigation should take place) of 4 pCi/L. in the basement and 0 on the first floor. But he has also purchased a continuous electronic monitoring unit (a Safety Siren Pro Series 3), which showed 6 pCi/L in the basement this past winter.

I have been running two Safety Siren Pro Series 3 units in my home off and on for more than 10 years, twice checking them against state of Vermont provided alpha tracker test kits run for at least three months in the winter. It’s important to check the electronic units over time because they can go wonky. I have found that levels correlate to cold weather and stack effectAlso referred to as the chimney effect, this is one of three primary forces that drives air leakage in buildings. When warm air is in a column (such as a building), its buoyancy pulls colder air in low in buildings as the buoyant air exerts pressure to escape out the top. The pressure of stack effect is proportional to the height of the column of air and the temperature difference between the air in the column and ambient air. Stack effect is much stronger in cold climates during the heating season than in hot climates during the cooling season. in my house: levels rise to 4 and above in the winter in my basement and move up and down with outdoor temperature (which I manage with an HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. dedicated to radon mitigation in the basement) until the spring, when levels move down to the 2 – 3 pCi/L range.

We don’t understand very well how airtightness correlates to radon levels, so it’s a good idea to keep your eye on radon levels as you make any space tighter, but particularly below-grade areas. And understand that any data you have on radon levels become part of the performance record of your home that must be disclosed if or when you sell your home.

Pin-type moisture content testing: I checked in with Justin on this because whenever you have wood framing in direct contact with masonry, it’s important to know how the moisture content of framing members in contact with masonry compares to the moisture content of framing that is not in contact. If temperature and relative humidity levels in your basement are stable, you can use an equivalent moisture content calculator to get a sense of capillaryForces that lift water or pull it through porous materials, such as concrete. The tendency of a material to wick water due to the surface tension of the water molecules. action, or the lack thereof, where framing members have no capillary break with the foundation.

Capillary break: Does Justin need to jack up house to get a capillary break under his sill beams? If the beams are sound and the moisture content by weight is similar to other framing in the basement, probably not. However, as Justin changes the hygrothermalA term used to characterize the temperature (thermal) and moisture (hygro) conditions particularly with respect to climate, both indoors and out. balance of the sill beams by air sealing and insulating around them, things can change. Insulating at the sill beams from the interior will make them colder and more sensitive to wetting. So, Justin should make every effort to keep them dry by managing surface water around his fieldstone foundation and consider insulating his above-grade foundation and sill beam from the exterior, using a water table detail to deal with the planar difference between the new exterior of that section of the wall and the clapboarded wall above. I recommend this because this approach warms the sill beam and leaves it open to inspection over time.

It’s just very cool that Justin has clearly been completely bitten and smitten by the building science bug, learning a ton — with quite a bit of that learning coming from GBA.


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Image Credits:

  1. Justin Brown

1.
Mar 5, 2018 12:11 PM ET

Great project.
by Steve Knapp CZ 3A Georgia

I really enjoy these member case studies. Great job GBA.

While looking at Justin's photos, the crawlspace ducts caught my eye. Should Justin add these to his to-do list? The ducts are not insulated, and I did not see any mastic on the joints. Is this a minor issue overall?


2.
Mar 6, 2018 11:13 AM ET

Ducts
by Justin Brown

The duct seams have been sealed with foil tape. I've weighed insulating them, but decided against it since it's tough to do with rigid foam. And ultimately, if I spray foam the fieldstone walls, I'm not sure it's necessary?


3.
Mar 8, 2018 6:04 AM ET

Spray foaming the fieldstone walls
by shane claflin

Some points to consider when looking at the old stone foundation:
1) Adding foam directly to the stone surface will change the hygrothermal balance, and thus the mortar composition and potential hydrostatic pressure.
2) Anything below the frostline (3 ft.) has a minimal delta T.
3) Once you add spray foam, you cannot remove it without great difficulty.
4) Is the delta T in this area great enough to justify that type of work?
5) The stone foundation is rather aesthetically pleasing, and had been structurally sound for literally hundreds of years.


4.
Mar 8, 2018 6:22 AM ET

Response to Shane Claflin
by Martin Holladay

Shane,
In the middle of a cold, snowless winter, when the ground has frozen to a depth of 3 feet, you're right that the soil that is 3 feet 1 inch below grade hasn't frozen yet. But that unfrozen soil can still be at 33°F or 34°F.

If your basement is at 65°F, is that "a minimal delta-T"? You decide. I think that the soil is cold enough to justify wall insulation. (Lots of people agree with me, including energy modelers and code officials.)

I agree that a fieldstone foundation is aesthetically pleasing. But homeowners rarely set up a sofa in the basement facing the foundation, so that they can invite their guests downstairs to admire the stonework while sipping Cabernet Sauvignon and listening to Bach. It's one of those aesthetic features of a house that, for better or worse, is rarely appreciated.


5.
Mar 14, 2018 10:36 AM ET

Follow-Ups
by Justin Brown

Scott, Peter, Martin & Dana, thanks so much for your feedback, it's been invaluable to me.

Radon: Since we last spoke, I added a sub-slab depressurization system with an RP145 fan, tied into my lower basement French drain. My slab was super leaky I couldn’t believe it! I spent days filling small cracks, and had to invert the fan from suck to blow (no jokes) to find the last few air leaks. System has been on 6 days and radon has dropped from 6 to 2.9pCi/L and dropping. Humidity has dropped from the mid-50% range, to the mid-40% range. Basement temp has held steady so I don’t think I’m losing conditioned air. This is without tapping into the crawlspace or upper sump/drain. Since radon is typically highest in winter, and I’ve got 24” of snow on the ground, I’m hoping my number will keep dropping to the low-2 or high 1pCi/L range with the current setup.

Basement framing moisture: I will begin monitoring my sill and basement framing as I assess spray foaming in the fieldstone – is 1x per week for 6 months or so good? Across all seasons I assume?

Capillary break: I will add gutters and try to manage exterior water. I prefer not to add exterior insulation. If I opt to use closed cell spray foam on interior fieldstone:

1) Any benefit to stopping the spray foam at or just below the sill to allow for some inward sill drying?
2) Spray the foam right on the rock, or add a plastic sheet/barrier on which to spray the foam?
3) Assuming the wood moisture issue is solved for, do you have any concerns about entombing the fieldstone, in terms of the mortar and stone itself? I realize we don’t have hundreds of years of data on this…

Regarding basement ceiling insulation, I currently have faced batts. Basement temps are hovering 55-59 since I’ve insulated the poured concrete with 3” Thermax. If I turn the heat off, temps in my “vented cathedral ceiling wing” drop to 50-52. Should I remove the batts from the basement ceiling? Any downside (colder floor?), or will that help basement heat migrate up?

And relatedly, I can’t tell you how much I don’t like my vented cathedral ceiling. Am I correct that my only real option for solving that would be to rip down the drywall ceiling, spray foam under the rafters, ditch the vents, and re-drywall? If so, seems hard to justify cost…if I remove an outlet in the wall in that section of the house, on a windy day I can feel the wind wash as the builder obviously didn’t air seal the wall top plates, so everything is communicating.

Thank you everyone.

Justin


6.
Mar 14, 2018 11:03 AM ET

Response to Justin Brown
by Martin Holladay

Justin,
Q. "If I opt to use closed cell spray foam on interior fieldstone, is there any benefit to stopping the spray foam at or just below the sill to allow for some inward sill drying?"

A. This is a judgment call. If you decide to leave your sill uninsulated, at least use caulk for air sealing.

Q. "If I opt to use closed cell spray foam on interior fieldstone, should I spray the foam right on the rock, or add a plastic sheet/barrier on which to spray the foam?"

A. If your foundation wall has a history of water entry, you may want to install dimple mat between the fieldstone and the spray foam. The dimple mat should lead to an interior French drain that leads to a sump. If your foundation wall has no history of water entry, you can apply the spray foam directly to the stones.

Q. "Assuming the wood moisture issue is resolved, do you have any concerns about entombing the fieldstone, in terms of the mortar and stone itself?"

A. No. Closed-cell spray foam adds structural strength to the stone wall, and can help hold loose stones in place.

Q. "Basement temps are hovering 55-59 since I’ve insulated the poured concrete with 3-inch Thermax. If I turn the heat off, temps in my 'vented cathedral ceiling wing' drop to 50-52. Should I remove the batts from the basement ceiling? Any downside (colder floor?), or will that help basement heat migrate up?"

A. If your basement is warmer than the room above, and you want more heat to rise to the room above, go ahead and remove the insulation between the two rooms.

Q. "I can’t tell you how much I don’t like my vented cathedral ceiling. Am I correct that my only real option for solving that would be to rip down the drywall ceiling, spray foam under the rafters, ditch the vents, and re-drywall?"

A. That's one approach. You can also install spray foam between the rafters from above, when it's time to re-roof. Or you can install a thick layer of rigid foam on the exterior side of your roof sheathing when you re-roof.


7.
Mar 15, 2018 12:37 PM ET

Edited Mar 15, 2018 12:38 PM ET.

Response to Martin
by Justin Brown

Q. "Basement temps are hovering 55-59 since I’ve insulated the poured concrete with 3-inch Thermax. If I turn the heat off, temps in my 'vented cathedral ceiling wing' drop to 50-52. Should I remove the batts from the basement ceiling? Any downside (colder floor?), or will that help basement heat migrate up?"

A. If your basement is warmer than the room above, and you want more heat to rise to the room above, go ahead and remove the insulation between the two rooms.

JB: Okay, and before I do this...is there any potential downside? Will this cause heat from my first floor to migrate to basement, or is that not really of concern given the basement is warmer in that section of the house?

And once I sprayfoam the fieldstone/totally insulate the basement walls, should I remove all fiberglass insulation from basement ceiling?

What may be confusing me, is that a family member had an energy company spray foam their foundation, but then also install thermax underneath the subfloor between the ceiling joists, which I thought was unnecessary if basement walls are insulated? That house does have radiant flooring however, which could be the difference?

Thank you, just want to be sure before I go rip it down.


8.
Mar 15, 2018 1:00 PM ET

Response to Justin Brown
by Martin Holladay

Justin,
When you basement is warmer than the room above, heat will flow from the basement to the room above.

When the room above the basement is warmer than the basement, heat will flow from the room above the basement to the basement. That's physics.

In general, when a basement has insulated walls, there is no need for insulation in the basement ceiling, unless (a) the insulation is part of a sound control strategy, or (b) the room above the basement has in-floor hydronic heating, and the homeowner wants to keep the basement cool.


9.
Mar 15, 2018 6:07 PM ET

Edited Mar 15, 2018 6:09 PM ET.

Response to Martin
by Justin Brown

Martin,

Thank you.

The area where I want to remove the basement ceiling insulation has a vented cathedral ceiling on the 1st floor above (and that 1st floor area is the only part of house that gets colder than the basement).

I just want to be sure encouraging that warmer basement air to migrate through a floor to an area under a vented cathedral ceiling won't cause a net heat loss. Forgive me if this is a silly question...so holding that heat in the basement provides no net benefit (thermal mass or otherwise) in the face of potential heat loss out the cathedral ceiling?

Just want to confirm -- thank you!

Oh and, do you also agree on removing unvented crawlspace fiberglass ceiling insulation, when the walls are insulated? And, if the wall on one side is more a "slope," and not a vertical wall, should the spray foam run down some of that slope/floor? Or just insulate the vertical?

Thanks again.


10.
Mar 16, 2018 5:03 AM ET

Response to Justin Brown
by Martin Holladay

Justin,
I don't think that removing the insulation in your basement ceiling is going to make a huge difference in the temperature of the room upstairs. But it will make some difference. The laws of physics require this to be true.

To the extent that you end up raising the temperature of the room above the basement, of course your rate of heat loss through the walls and ceiling of the room above the basement will increase slightly -- because the rate of heat loss through these walls and the ceiling depend on the delta-T. If you make the room warmer, the room will lose heat to the outdoors faster, and you will use more fuel. Again, that's physics.

If you want the room above the basement to be warmer, you'll need to burn some fuel to achieve that goal. If you want to save fuel, keep the room as cool as possible.

Q. "Do you also agree on removing unvented crawlspace fiberglass ceiling insulation, when the walls are insulated?"

A. Yes -- because fiberglass insulation above a crawl space often deteriorates and is hard to maintain in good condition. But if the fiberglass insulation is in good condition, removing it isn't urgent (or even necessary, as long as the pipes aren't in danger of freezing). For more information, see Building an Unvented Crawl Space.

Q. "If the wall on one side is more a 'slope,' and not a vertical wall, should the spray foam run down some of that slope/floor? Or just insulate the vertical?"

A. If you have a crawl space wall that leans, I might call up an engineer to evaluate the soundness of the wall. But if an engineer says that the wall is structurally sound, I would insulate all of it.


11.
Mar 16, 2018 9:09 AM ET

Response to Martin
by Justin Brown

Martin,

You are awesome, thank you.

“If you want the room above the basement to be warmer, you'll need to burn some fuel to achieve that goal. If you want to save fuel, keep the room as cool as possible.”

JB: Thank you. I apologize if you feel you’ve answered this and I’m being daft: assuming no changes to thermostat settings, does removing basement ceiling insulation and encouraging (albeit minor) heat migration up from a warmer basement accelerate total house heat loss, or simply change the walls (1st floor vs basement) through which the heat dissipates?

“A. Yes -- because fiberglass insulation above a crawl space often deteriorates and is hard to maintain in good condition. But if the fiberglass insulation is in good condition, removing it isn't urgent (or even necessary, as long as the pipes aren't in danger of freezing). For more information, see Building an Unvented Crawl Space.”

JB: It is in good condition. Crawlspace temp in winter is about 55-59F. I just am not 100% clear on whether, once the crawlspace and basement walls are 100% insulated and the basement is 100% in the thermal envelope, leaving the basement ceiling insulation detracts from, or enhances, overall heating efficiency?

“A. If you have a crawl space wall that leans, I might call up an engineer to evaluate the soundness of the wall. But if an engineer says that the wall is structurally sound, I would insulate all of it.”

JB: It’s not a leaning wall, but rather the crawlspace ground slopes from about 4’ of height clearance to about 1.5’ where it meets the rim joist (there is a picture on the blog). My question is, in a situation where there isn’t a full wall, should I spray foam insulate some of the poly-covered ground of that slope, or only the vertical surfaces?


12.
Mar 16, 2018 9:17 AM ET

Edited Mar 16, 2018 9:18 AM ET.

Response to Justin Brown
by Martin Holladay

Justin,
Q. "Assuming no changes to thermostat settings, does removing basement ceiling insulation and encouraging (albeit minor) heat migration up from a warmer basement accelerate total house heat loss, or simply change the walls (1st floor vs basement) through which the heat dissipates?"

A. To a minor extent, the change you describe would increase the rate of heat loss, because you would be sending heat upstairs to raise the temperature of the room above.

Q. "I just am not 100% clear on whether, once the crawlspace and basement walls are 100% insulated and the basement is 100% in the thermal envelope, leaving the basement ceiling insulation detracts from, or enhances, overall heating efficiency?"

A. Heating efficiency is determined by the type of boiler or furnace you have. I think you mean "overall fuel use." It's unclear whether removing the crawlspace ceiling insulation will change your annual fuel use. It depends partly on whether you have any heating equipment or heating appliances in the crawl space.

Q. "It’s not a leaning wall, but rather the crawlspace ground slopes from about 4’ of height clearance to about 1.5’ where it meets the rim joist (there is a picture on the blog). My question is, in a situation where there isn’t a full wall, should I spray foam insulate some of the poly-covered ground of that slope, or only the vertical surfaces?"

A. Insulating the floor of a crawl space is rarely cost-effective in terms of energy use. Don't bother to install spray foam on the floor.


13.
Mar 16, 2018 10:10 AM ET

Response to Martin
by Justin Brown

Martin,

“A. Heating efficiency is determined by the type of boiler or furnace you have. I think you mean "overall fuel use." It's unclear whether removing the crawlspace ceiling insulation will change your annual fuel use. It depends partly on whether you have any heating equipment or heating appliances in the crawl space.”

Yes, I mean overall fuel use. System 2000 boiler is in the fieldstone basement adjacent to the crawlspace. So it sounds like it’s best to assess framing moisture, and if I proceed with spray foaming the fieldstone, re-assess basement temps and determine at that point whether removing the basement ceiling insulation makes sense?

Thank you.


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