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All About Water-Resistive Barriers

How to choose between asphalt felt, Grade D building paper, housewrap, and a few exotic WRBs

Posted on Jan 21 2011 by Martin Holladay

UPDATED on September 18, 2013

By now, almost all builders know the importance of installing a water-resistive barrierSometimes also called the weather-resistive barrier, this layer of any wall assembly is the material interior to the wall cladding that forms a secondary drainage plane for liquid water that makes it past the cladding. This layer can be building paper, housewrap, or even a fluid-applied material. (WRB) behind siding. Most types of siding leak, so it’s a good idea (and a code requirement) to install a WRB to protect your wall 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. from any wind-driven rain that gets past the siding.

A WRB can be vapor-permeable, like Tyvek, or vapor-impermeable, like foil-faced polyisocyanurate. As long as the wall assembly is designed to dry out when it gets wet, either vapor-permeable or vapor-impermeable WRBs work well.

In most cases, WRBs are not air barriers. (The notable exceptions are Zip System sheathing and liquid-applied WRBs.) If you want to create an air barrier on the exterior side of your wall, it usually makes more sense to create the air barrier at the sheathing layer, not at the WRB.

Although there are at least six categories of WRB — asphalt felt, Grade D building paperTypically referring to Grade D building paper, this product is an asphalt-impregnated kraft paper that looks a lot like a lightweight asphalt felt. The Grade D designation has come to mean that the building paper passes ASTM D779 (minimum 10-minute rating with the “boat test”) and different products are called out as “30-minute” or even “60-minute” based on D779 results. At times confused with roofing felt, roofing felts and building paper differ in two ways: felts are made of recycled-content paper, building papers of virgin paper; felts are made of a heavier stock paper; building papers a lighter stock. See also roofing felt., plastic housewrap, liquid-applied WRBs, rigid foam, and Zip System sheathing — building codes calls for just one: asphalt felt. (One other category — three-dimensional vapor-impermeable barriers — is represented by a single product, Delta-Dry. Although it is often used as a WRB, Delta-Dry has not received code approval as a substitute for code-required WRBs.)

According to the IRC, you need asphalt felt

In section R703.2, the International Residential Code requires builders to install a layer of number 15 asphalt felt or paperbacked stucco lath over the wall sheathing or studs of every new home. The requirement includes a qualification: if you don’t want to use number 15 asphalt felt, you can use some “other approved water-resistive barrier.”

The code requirement calling for walls to be covered with asphalt felt is rather odd, because every asphalt felt manufacturer declares unequivocally that the product is intended for roofs, not walls. When builders install asphalt felt on walls as required by code, the manufacturer of the felt considers the application to be outside of the product’s intended use. In spite of this curious anomaly, asphalt felt performs well when used over wall sheathing as a WRB.

According to tests performed by the International Code Council Evaluation Service (ICC-ESThis is the International Code Council Evaluation Service. ICC-ES is a non-profit public benefit corporation that evaluates building products, issuing final reports on code compliance of building products and materials. These reports on then made available at no charge to the building community at large.), several products have been approved as substitutes for number 15 asphalt felt, including Grade D building paper, plastic housewraps like Tyvek and Typar, liquid-applied WRBs like StoGuard or Tyvek Fluid Applied WB, and certain building assemblies that include rigid foam.

(Just to make matters more confusing, the International Residential Code has a second reference to WRBs in addition to the one in section R703.2 mentioned above. Section R703.6.3 requires that “Water-resistive barriers shall be installed as required in Section R703.2 and, where applied over wood-based sheathing, shall include a water-resistive vapor-permeable barrier with a performance at least equivalent to two layers of Grade D paper.” Although section R703.2 bases the performance of a WRB on the performance of #15 asphalt felt, and section R703.6.3 bases the performance of a WRB on a different product, Grade D paper, the two provisions of the code are not contradictory, since most approved WRBs meet both provisions. The different language in these two sections is a historical accident as well as a glaring example of bad code writing.)

Asphalt felt

One hundred years ago, asphalt felt was a true cloth felt made from recycled cotton rags. Since asphalt felt is now made from a mixture of recycled corrugated paper and sawdust, the term “felt” is a misnomer.

Over the years, asphalt felt keeps getting lighter. “In the old days, it used to weigh 15 pounds per 100 square feet, but not anymore,” explained Allen Snyder, a product engineer at CertainTeed, a manufacturer of asphalt felt.

The main reason that manufacturers have reduced the weight of asphalt felts is to lower their manufacturing costs. “The whole issue comes down to price,” said Ed Todd, technical manager at Atlas Roofing, an asphalt felt manufacturer in Atlanta. Since today’s asphalt felts weight between 7 and 14 pounds per square, manufacturers no longer call the product 15-pound felt; instead, it has been renamed “number 15” felt.

ASTMAmerican Society for Testing and Materials. Not-for-profit international standards organization that provides a forum for the development and publication of voluntary technical standards for materials, products, systems, and services. Originally the American Society for Testing and Materials. has established two standards for asphalt felt. The less stringent standard, ASTM D 4869, requires #15 felt to weigh at least 8 pounds per 100 square feet. The more rigorous standard, ASTM D 226, requires a minimum weight of 11.5 pounds per square. According to the IRC, any asphalt felt used as a WRB on walls must be Type 1 felt complying with ASTM D 226.

Because enforcement of the code requirement for ASTM D 226 felt is relatively lax, most lumberyards stock only lightweight asphalt felt with no ASTM rating; such felt typically weighs only 7.6 pounds per square. In areas of the country with more stringent code enforcement — notably Florida — ASTM-rated felt is widely available.

Asphalt felt is also available in a heavier version, commonly called 30-pound felt. This #30 felt is available in both unrated grades (15.7 to 19.9 lbs. per square) and ASTM-rated grades (26.4 to 27.3 lbs. per square). Since the lightest unrated #30 asphalt felt is still heavier than the heaviest ASTM-rated #15 felt, it a logical choice for builders in search of a felt that approximates the asphalt felt used by their grandparents.

Asphalt felt has a permeance of only 5 perms when dry, but a much higher rating of 60 perms when wet. Fans of felt note one of its advantages over housewrap: if water gets behind felt — either due to a flashing leak or condensation from solar-driven moisture — the felt can soak up the liquid water and gradually dry to the exterior. Plastic housewrap is not absorbent; any water trapped on the wrong side of plastic housewrap can only pass through to the exterior as vapor.

Grade D building paper

Builders in the western U.S., especially in areas where stucco is common, are familiar with Grade D building paper. In much of the rest of the country, however, including most of the East Coast, Grade D building paper is virtually unknown. Although Grade D paper is most often used under stucco, manufacturers point out that it can be used under any kind of siding.

Grade D building paper is an asphalt-impregnated kraft paper that looks like a lightweight asphalt felt. The term “Grade D” originated with federal specification (UU-B-790) which dates back to 1968. The specification requires that Grade D paper have a minimum water-resistance rating of 10 minutes and a minimum water vapor transmission rate that corresponds to a permeance rating of about 5 perms.

The water-resistance rating is based on a test, ASTM D 779, usually called the “boat test.” If a piece of building paper or housewrap folded into the shape of a toy boat can float in a dish of water and withstand soaking for at least 10 minutes, it meets the water-resistance requirements of the Grade D specification.

Many Grade D manufacturers choose to exceed the minimum water-resistance rating, producing 20-minute, 30-minute, or 60-minute papers. Although the UBC referred to these Grade D papers as “waterproof” papers, even a 60-minute paper is, at best, only water-resistant.

Like asphalt felt, Grade D building paper is an asphalt-saturated paper. It differs from asphalt felt in two ways: it uses a lighter-weight paper, and the paper is made from new paper pulp rather than recycled cardboard. Since Grade D paper weighs less than asphalt felt, it also costs less.

Manufacturers of Grade D paper like to point out that because it is lighter, it is easier to crease and install in inside corners. Some experts note, however, that the added thickness of #15 felt is one of its virtues. If Grade D paper gets wet and stays wet, it can rot. Although asphalt felt can also rot, its heavier weight helps it hold up better in extreme conditions.

Because a single layer of Grade D paper may not withstand repeated wetting, the use of two layers of building paper has become a standard detail under many types of siding. But in areas that get a lot of rain, even two layers of building paper can be overcome by regular soakings. “I’ve seen building paper rot, even if you have two layers,” building scientist Joe Lstiburek told me. “Grade D paper rots faster than roofing feltOriginally made with cotton rag content, this asphalt saturated product is now made of paper. At times confused with building paper, roofing felts and building paper differ in two ways: felts are made of recycled-content paper, building papers of virgin paper; felts are made of a heavier stock paper; building papers a lighter stock. ASTM qualifies roofing felts with the following ratings: ASTM D4869 (Type 1 with a minimum weight of 8 pounds per 100 square feet) and ASTM D226 (Type 2 with a minimum weight of 11.5 pounds per 100 square feet). “#15” felt used to weigh 15 pounds per 100 square feet, but not anymore; non-ASTM felts can weigh as little as 7 pounds per 100 square feet. Although felts do not bend as easily as building paper, felts are commonly used or even preferred on walls because of their ability to hold more water without deterioration. See also building paper.. The best paper for a wall is a roofing felt.”

According to Wesley Page, a retired waterproofing consultant from Novato, Calif., Grade D paper cannot withstand repeated wetting. “Grade D building paper will fail completely if it gets wet,” said Page. “It just disintegrates and disappears.” All experts agree that any paper or felt will be less likely to rot if it is installed behind an air space that permits drainage and speeds drying.

Plastic housewraps

Plastic housewraps are made from one of several polyolefin fabrics, generally either polyethylene or polypropylene. Different brands of housewrap have different levels of vapor permeance; the range is from 6 to 59 perms.

Most building science experts downplay the importance of a housewrap’s vapor permeance. In theory, if a wall cavity gets wet, a WRB should be vapor permeable enough to allow the wall to dry to the exterior. Yet the ideal WRB would also prevent water vapor from being driven into a wall by inward solar vapor drive. Unfortunately, no one has yet developed a material that has “one-way permeance,” allowing vapor out but not in. High vapor permeance is probably a desirable feature in a WRB during cold winter weather, but may be undesirable during hot, humid weather, when the action of the sun on saturated siding can cause vapor to be driven into a wall.

According to Lstiburek, the permeance of a WRB “matters very little.” Most types of sheathing, including OSB and plywood, are not very vapor-permeable, at least when dry. “Asphalt felt is rated at 5 perms, and the housewraps have ratings that range from 5 to 50,” said Brad Allshouse, vice-president of marketing for Simplex Products, a housewrap manufacturer. “But commonly used sheathings have a permeance rating of less than 1. So the permeance of the housewrap is a moot point. A housewrap with a perm rating more than the code minimum of 5 is overkill.”

Housewraps can be divided into two categories: perforated and non-perforated. Non-perforated housewraps allow water vapor to pass between the fibers of the plastic fabric, while perforated housewraps are made from vapor-tight plastic films that are needle-punched with small holes to allow the passage of water vapor. Laboratory tests have shown that the non-perforated housewraps resist liquid water better than the perforated housewraps.

Some surfactants, which are chemical extractives that can leach out of wet cedar or redwood siding, have the potential to degrade the water resistance of plastic housewrap. However, surfactants can also degrade asphalt felt. “There have been problems with cedar and redwood sidings leaching wood sugars or surfactants,” said Lstiburek. “This has occurred with all the plastic housewraps and the felts. Everything is affected. But the plastics seem to have more of a problem than the felts.”

Plastic housewraps are rarely used under stucco. “You can’t stick stucco to any plastic housewrap, because if the stucco is in direct contact with a housewrap, the housewrap loses its water repellency,” said Lstiburek. Frank Nunes, an officer with the International Institute of Lath and Plaster, has also seen problems using housewrap behind stucco. “Some housewraps are very reactive to surfactants in the cement plaster,” says Nunes. “In one case I observed, the resins of the housewrap dissolved, leaving the fibers. It looked like a silkscreen — there was no material left.” (Because many areas of the country have suffered clusters of wet-wall failures behind stucco, most experts now recommend that stucco should always be installed over a ventilated air space. To learn more, read “To Install Stucco Right, Include an Air Gap.”)

If a wall is well designed and well flashed, any of the plastic housewraps will do the job. “The design of the wall is more important than the choice of housewrap,” said John Straube. Since the most important function of a WRB is to resist liquid water, you should probably choose a non-perforated housewrap (for example, Tyvek, Typar, R-Wrap, or Weathermate Plus) over a perforated one (for example, Barricade, PinkWrap, or Weathermate). “If I want to keep the water out, maybe I wouldn’t choose a housewrap with a whole bunch of holes punched in it,” says Straube. Not all experts agree, however. “All housewraps are perforated, because they are stapled or nailed,” said Joe Lstiburek. “Whether or not they come from the factory perforated is irrelevant.”

In general, housewraps cost more than building paper or asphalt felt. Most builders find that housewrap is easier to install than paper or felt, because it comes in wide rolls (usually 9 or 10 feet wide) and it weighs less. On the other hand, builders working alone or working on a very high building may find a wide roll of housewrap more awkward than a narrow roll of paper or felt.

Housewraps stay more flexible in cold temperatures than paper or felt, and they resist tearing better. However, asphalt felt is better able to seal around fastener holes than housewrap.

On the average job site, housewrap is almost never installed as carefully as it is when tested in a laboratory. After performing a field survey of installed housewrap, researchers from the Pennsylvania Housing Research Center reported, “In the majority of the houses where staples have been installed with an automatic staple gun, tears and holes in the housewrap were common.” One possible solution to this problem is to switch to plastic-cap nails, which provide much better sealing than staples.

Wrinkled housewraps

Although most WRBs are able to protect sheathing from occasional wind-driven rain, a WRB can’t act as a drainage planePath that water would take over the building envelope. Concealed drainage-plane materials, such as building paper or housewrap, are designed to shed water that penetrates the building’s cladding. Drainage planes are installed to overlap in shingle fashion (weatherlap) so that water flows downward and away from the building envelope. unless there is an air gap between the WRB and the siding to create a rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. . This can be done by installing vertical 1x4 strapping or by using a three-dimensional plastic mesh product like Cedar Breather or .

A third approach is to use wrinkled housewrap — a type of housewrap that has small vertical corrugations. Examples of such products include , , , , , , , , and .

In order to evaluate these products, one question arises: How thick does a corrugation need to be in order for water to drain? Unfortunately, building experts disagree on this issue, which awaits further research. “An air gap does not have be 3/4 inch,” says Mark Bomberg, editor of Journal of Thermal Envelope and Building Science. “I am quite happy with an air gap that is less than 1/8 inch. It does not ventilate, but it allows local drainage.”

StuccoWrap’s wrinkles are much shallower than 1/8 inch; in fact, they are less than 20 thousands of an inch high. Products that marry a three-dimensional plastic drainage mat with a conventional WRB — for example, EnkaBarrier and Home Slicker Plus Typar — are likely to provide better drainage than wrinkled housewraps like StuccoWrap, RainDrop, or Vortec.

Rigid foam

It is possible to use foam sheathing as a water-resistive barrier (WRB). However, not all brands of rigid foam have been approved for this purpose.

Even if you choose a code-approved foam, you can run afoul of your local building inspector if you don’t follow strict fastening and seam-sealing details. Moreover, some building experts note that rigid foam can shrink, leading to worries that even excellent installations of rigid foam (using an approved foam and approved seam-sealing details) may not be durable enough to create a dependable WRB.

To learn more about the use of rigid foam as a WRB, see Using Rigid Foam As a Water-Resistive Barrier.

Liquid-applied WRBs

Liquid-applied WRBs come in a bucket and are applied to wall sheathing or concrete blocks with a roller or a spray rig. These products cure to form a tenacious, flexible coating that seals small cracks and penetrations.

Although liquid-applied WRBs cost more than housewrap, they also perform better. If air tightness is important to you, and your construction budget can handle the cost, a liquid-applied WRB may make sense.

For more information on liquid-applied WRBs, see Housewrap in a Can: Liquid-Applied WRBs.

Zip System sheathing

is a proprietary 7/16-inch thick OSB panel manufactured by Huber Engineered Woods. Huber advises builders using its Zip System sheathing to tape the seams between the panels with a special tape (Zip System tape), a 3¾-inch-wide polyolefin tape with an acrylic adhesive.

According to Huber, walls sheathed with properly taped Zip System panels do not require any housewrap; the taped panels function as a WRB. The International Code Council Evaluation Service has issued recognizing Zip System wall sheathing as an acceptable alternate to asphalt felt. The main advantage of Zip System sheathing, according to the manufacturer, is ease of installation: “Simply install the panels, tape the seams, and you have a complete structural wall system and a water-resistive barrier all-in-one.”

According to Michael Pyle, a Huber manager, Zip System panels are more water-resistant than ordinary OSB or AdvanTech OSB because they contain a “medium-density, phenolic-impregnated, kraft paper overlay” — in other words, an outer layer of plastic-impregnated paper.

Zip System wall sheathing can be used under most types of siding, including brick veneer. It can be used under wood siding, but only if the siding is back-primed or back-painted before installation. If used under cedar shingles, the manufacturer advises that the Zip System sheathing should first be covered with a layer of Cedar Breather or Home Slicker. If used under stucco, the Zip System sheathing must be covered by at least one layer of Grade D paper. Zip System tape cannot be installed in rainy weather, nor in weather colder than 20°F. Once the tape has been installed, it must be protected by siding within 180 days.

When it was first introduced to the market, Huber offered a warranty on their Zip System panels but refused to offer a warranty on the tape. However, Huber has recently improved their warranty, which now covers the tape as well as the sheathing panels for 30 years. There is a strange wrinkle in the warranty, however: the warranty specifically excludes coverage in a home that has “deterioration of the exterior roof or wall.” This exclusion is odd; taken literally (the way lawyers usually interpret such documents), it is a circular provision that should prevent Huber from honoring any warranty claims. Presumably, the only homeowners or builders who might need a warranty are those with deterioration of the exterior roof or wall. (Homeowner to warranty rep: “If my wall wasn’t deteriorated, I wouldn’t be calling you!”)

Builders who switch to Zip System wall sheathing will have to change some of their flashing details. Those who usually install conventional housewrap are accustomed to lapping the housewrap over window Z-flashing and other penetration flashings, so that gravity helps keep their walls dry. With Zip System wall sheathing, on the other hand, keeping the wall dry depends on chemistry — that is, on the adhesive component of Zip System tape and AC148 flashing tape.

John Straube, a professor of 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. Science at the University of Waterloo in Ontario, is familiar with the Zip System components. “It’s a high quality tape,” Straube told me. “It’s better than any other tape I’ve seen before.” Yet Straube is reluctant to speculate on the longevity of the tape’s bond. “The quality of the installation depends on the adhesion and on workmanship,” he says. “At the end of the day, we don’t know how it will adhere in the long run. It is an unanswerable question.”

According to Straube, one of the Zip System’s best features is that “it is a wonderful air barrier.” As most builders of energy-efficient homes realize, that’s nothing to sneeze at. Many builders who appreciate this fact use Zip System sheathing as part of their air barrier — while still using housewrap, since housewrap can be lapped over window flashings and may be more dependable than Zip System tape.


One relatively new product, , differs in several important ways from most WRBs:

  • Although Delta-Dry is vapor-impermeable, it still allows a wall to dry to the exterior.
  • Delta-Dry is a barrier to inward solar vapor drive.

Although Delta-Dry can fulfill the role of a WRB, it is classified as a “rainscreen product” and has not obtained approval by the International Code Council Evaluation Service for use as a WRB. If you want to use Delta-Dry, you'll probably have to use a housewrap behind it.

Delta-Dry is a membrane made of 22-mil high-density polyethylene. After a thermoforming process, the polyethylene is stiff enough to retain a three-dimensional egg-carton configuration. The total thickness of Delta-Dry is about ½ inch.

The manufacturer of Delta-Dry, Cosella-Dörken, has developed the product for installation over OSB or plywood sheathing. Because of Delta-Dry’s stiffness, the product creates two air spaces: a gap between the siding and the Delta-Dry, as well as a gap between the Delta-Dry and the wall sheathing.

While most housewraps depend on vapor diffusionMovement of water vapor through a material; water vapor can diffuse through even solid materials if the permeability is high enough. to help walls dry, Delta-Dry depends upon air movement (ventilation) between the Delta-Dry and the wall sheathing. Although Delta-Dry is as vapor-impermeable as 6-mil poly, its grooves allow air to move behind it, carrying moisture away from the sheathing.

Like most WRBs, Delta-Dry protects wall sheathing from any wind-driven rain that sneaks past the siding. Unlike such conventional WRBs as asphalt felt or Tyvek, however, Delta-Dry has air channels that provide a 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. break and a rainscreen between the siding and the sheathing, facilitating the drainage of liquid water.

Delta-Dry also beats felt or Tyvek when it comes to handling solar-driven moisture; since Delta-Dry is vapor-impermeable, it is a total barrier to inward solar vapor drive.

Delta-Dry is easily cut with scissors or a utility knife. It must be fastened to the underlying sheathing every 12 to 16 inches in both directions, using ½-inch roofing nails or ¾-inch staples. Each roll of Delta-Dry measures 39 inches by 50 feet; horizontal seams should have a shingle-style overlap of 3 inches.

To be sure that damp sheathing has a chance to dry out, the top and bottom edges of the Delta-Dry must allow for air movement through the gaps behind the product. When Delta-Dry is installed behind stucco, ventilation holes at the bottom of the wall are assured by installing lengths of drainage track with weep holes. When installed behind brick, Delta-Dry is folded at the base of the wall so that it extends flush with the outer face of the brickwork.

There are several possible ways to detail the top of a wall. Perhaps the simplest detail is to extend the Delta-Dry membrane into the soffit. Alternatively, the siding installer can leave a ¾ -inch gap between the top of the siding and the bottom of the soffit. Of course, the ventilation gaps at the bottom and top of the wall must never be caulked.

Cosella-Dörken arranged for Delta-Dry to be tested by building scientist John Straube, who measured the performance of the new WRB in a lab, and by the Oak Ridge National Laboratory’s Achilles Karagiozis, who conducted computer modeling studies of the product. In both cases, the results look good. Straube and Karagiozis concluded that wind and sunlight can drive enough ventilation air through Delta-Dry’s channels to remove significant amounts of moisture from wood sheathing. Straube told me, “It does seem to work better than asphalt felt, especially behind highly absorbent claddings like stucco, brick, or cultured stone. It makes a lot of sense behind adhered veneers. The only caveat is that you need to let air get behind it — there could be problems if someone were to try to seal the air gap at the bottom of the wall.”

Delta-Dry costs about 70 cents per square foot ($114 per roll).

Are WRBs waterproof?

When it comes to resisting liquid water, liquid-applied WRBs and Delta-Dry appear to be the most waterproof, followed by non-perforated housewraps and asphalt felt. Grade D building paper and perforated housewraps trail far behind.

But most conventional WRBs — including most housewraps, asphalt felt, and Grade D paper — can’t keep water at bay for long. “Everyone seems to think of building paper as a moisture barrier,” said George Tsongas, a former professor of mechanical engineering at Portland State University. “In fact, they are not moisture barriers. If you get any significant amount of water behind the siding, the building paper will not hold back water — not even 15-pound felt. All the papers will allow liquid water to go through them in one day.”

Moisture problems in walls are best avoided by good wall design and proper flashing; the choice of WRB is a secondary concern. Regardless of which WRB you choose, including a ventilated rainscreen gap between your siding and your sheathing will go a long ways toward reducing any chance of wet-wall problems.

Portions of this article appeared in and in Energy Design Update.

Last week’s blog: “Questions and Answers About Air Barriers.”

Tags: , , , , , , ,

Image Credits:

  1. Fine Homebuilding
  2. Cosella-Dörken Products

Jan 21, 2011 8:05 AM ET

What about Zip?
by Larry

I can't believe you'd write an exhaustive description of all these different types of water barriers and not mention Zip sheathing. Why is that?

Jan 21, 2011 8:08 AM ET

Drainage Plane for Stucco
by Allan Edwards


Is there any evidence that the back side (the side against the WRB) of the first coat of 3 coat stucco (scratch coat) actually has significant holes and gaps that allow for water to drain? Someone told me that as that first coat dries and cures that it pulls away from the house a very small amount, but enough that it creates some capillary potential. I know the front side of the scratch coat that you see has a lot of roughness and uneveness to it. I will say one thing I've noticed is you never see much evidence of water draining through the weep screeds of stucco. Makes me wonder where all of that moisture is going, surely it can't all dry to the interior of the house.

Jan 21, 2011 8:20 AM ET

Edited Jan 21, 2011 11:25 AM ET.

Response to Larry
by Martin Holladay

Good point! I have edited the blog to include information on Zip System sheathing.

Thanks for the excellent suggestion.

Jan 21, 2011 8:30 AM ET

30 lb felt
by Allan Edwards

Why is 30lb never mentioned, and what measurable benefits does it have over 15 lb? When I do brick or stone houses I always put 30lb over Tyvek and plywood sheathing.

Jan 21, 2011 9:29 AM ET

Response to Allan Edwards
by Martin Holladay

You're skimming instead of reading. There's a whole paragraph on 30-pound felt. Here it is again, in case you're having a hard time finding it:

"Asphalt felt is also available in a heavier version, commonly called 30-pound felt. This #30 felt is available in both unrated grades (15.7 to 19.9 lbs. per square) and ASTM-rated grades (26.4 to 27.3 lb.s per square). Since the lightest unrated #30 asphalt felt is still heavier than the heaviest ASTM-rated #15 felt, it a logical choice for builders in search of a felt that approximates the asphalt felt used by their grandparents."

Jan 21, 2011 9:40 AM ET

On drainage planes for stucco
by Martin Holladay

For years, stucco contractors said that wet stucco caused the outer layer of Grade D paper (assuming two layers of Grade D) to get wet, and that this outer layer of Grade D paper would pucker as it dried out, allowing some drainage.

There is some evidence of this phenomenon, but there is also ample evidence that OSB sheathing under stucco with two layers of Grade D paper can rot due to insufficient drying. So whatever puckering is occurring is clearly not enough for drainage or rapid drying.

I stand by my earlier blog, in which I stated that it is risky to install stucco without a drainage gap between the stucco and the underlying sheathing -- especially if you are using OSB. And when I write about a drainage gap, I mean a real air gap created with the three-dimensional plastic matrix, not just puckered Grade D paper.

Jan 21, 2011 10:15 AM ET

Question for Martin
by Allan Edwards

Sorry about missing the 30# felt info, it was early in the morning. I've always used CDX plywood for sheathing, never cared for OSB because I felt instintively that it couldn't take water like plywood. Although I will say plywood is just a bunch of veneers glued together, so it's not like it is a total "real wood product".

I switched to Zip Wall, wondered if the OSB aspect is completely removed as a moisture/water issue if you tape the seams properly. This would be in a stucco application. Also, do multiple WRB give you eough protection (I know you recommend a drainage plane). The coating on the Zip Wall is considered some kind of WRB protection, I also apply Tyvek then one layer of grade D paper, then lath and stucco, so I am using 3 WRB layers.

I pay close attention to flashing and in fact all of my flashings are copper. I'm looking for the Martin Holliday Seal of Approval :)

Jan 21, 2011 11:34 AM ET

Stucco without a drainage gap
by Martin Holladay

So, you use Zip System sheathing, then three layers of WRB, then stucco. Frankly, I don't have enough experience or data to know how your walls will look in 10 or 15 years. It sounds like a better job than many contractors do (ordinary OSB and 2 layers of Grade D paper). But I just don't know if your system is robust enough to keep you out of trouble.

Stucco can be scary, because it's slow to dry. It's also a siding type that makes inspection of the sheathing very difficult (unlike vinyl). If I were installing stucco, I'd want an air gap -- but that's probably because I've seen so many gruesome photos of stucco disasters and sheathing rot.

Jan 21, 2011 11:38 AM ET

so -- local best practice?
by 5C8rvfuWev

Martin, this is another great overview ... thanks from the peanut gallery.

With 48 inches of average annual rainfall, the need for a rainscreen with a good WRB is underlined in this area. We get lots of sun, and when there isn't a drought, lots of water.

For the bungalow we're planning, I've anticipated a 3/4" 1x3 furring rainscreen over #15 felt/1" rigid foam/more felt/plywood. But I wonder if that is the best (or the most cost effective) choice. I would anticipate extra labor in detailing the 1x3, plus the breakdown of the rainscreen every 16"/24" when a new furring strip is applied.

As Martin says in the blog, even the best minds aren't sure how much rainscreen is enough in a given climate.

But I believe that using HomeSlicker (equiv) (unlike 3/4" furring) might save considerable labor and would provide consistent coverage over the enclosure. Am I being too scrupulous (as I tend to be) thinking HomeSlicker may not provide enough drainage over the felt for long term effectiveness and is therefore (to me) a risk not worth the savings?

Delta Dry is more expensive than HomeSlicker but provides more room (1/2") for drainage. It too would provide consistent coverage for walls. Whaddya think?

So, making it into one question -- if you had to decide, based on the evidence available now, which choice would make the most effective rainscreen and most cost effective iinstallation?

I'll appreciate your opinions. And count on y'all to point out things I don't know to consider, lol.

Jan 21, 2011 11:53 AM ET

Response to Joe
by Martin Holladay

I wouldn't hesitate to use Homeslicker. I'm sure it will provide adequate drainage and ventilation, as long as your other details are good.

Most builders find that vertical 1x3 or 1x4 strapping is cheaper than Homeslicker. But either option should perform very well.

I don't think you need two layers of asphalt felt, although they can't hurt. If you want to simplify your wall, choose one layer as your WRB -- make it the layer that is integrated with your window flashings -- instead of installing the felt twice.

Jan 21, 2011 12:36 PM ET

Re: What about Zip?
by Larry

Thanks Martin for the update including the Zip system. I'm guess I'm still feeling a bit squeamish about Zip since you voiced some reservations about using OSB sheathing in an earlier post. When we chose the Zip system for our house I was mainly concerned with air sealing. But as I read more, I've become concerned about Zip's longevity enough to consider adding a house wrap over the zip just to be sure. Thanks again for a great energy nerd post.

Jan 21, 2011 1:55 PM ET

by Carl Seville

Martin -good overview of a very important subject. I have used Delta Dry in the past and like it quite a bit. I'm glad you pointed out the need for vents at top and bottom, this is a detail that is often missed.

It has been a few years, but the last I heard from the manufacturer, Delta Dry is not code approved as a WRB, only as a vented rainscreen, although it should function fine by itself without a separate WRB. Do you have more recent information that says otherwise?

Jan 21, 2011 2:01 PM ET

Is Delta-Dry approved as a WRB?
by Martin Holladay

Thanks very much for your comment. You are right; Delta-Dry has not been approved as a WRB by the ICC-ES. I just confirmed that fact by calling the manufacturer.

That's an important point, and I'll edit my blog to reflect that fact. Thanks again.

Jan 22, 2011 12:05 PM ET

plastic housewraps
by j chesnut

Does anyone know if the plastic housewraps products have improved over the years? I hear rumors every once in awhile from builders that they used to have problems of one sort or another with these products but the product manufactures have addressed the problems. Rapid UV degradation, surfactant degradation, loss of permeability, loss of capacity to resist water infiltration for example. Any evidence to support these claims?

Jan 22, 2011 12:39 PM ET

Have housewraps improved?
by Martin Holladay

Your question is too general for an easy, quick answer. But I know for a fact that after Tyvek was embarrassed by a series of well-documented Tyvek failures, some due to degradation by UV light exposure, and some due to problems arising from cedar extractives, Tyvek was reformulated in a way that, by most accounts, represented an improvement.

Jan 22, 2011 1:12 PM ET

by j chesnut

Tyvek dominates the market here. This sounds precisely like what I have heard. Good to know that it wasn't simply an urban myth spreading around.

Jan 22, 2011 4:55 PM ET

Fastening Tyvek to exterior side of rigid foam sheathing
by Joe Chalat

Tyvek's installation instructions call for fastening the membrane into the studs and not just the sheathing. Their 1 3/4" steel stud screw makes a substantial connection back into the stud. I could not find a recommendation for fastening the Tyvek over rigid foam sheathing. would you use screws that are long enough to have the same depth in each stud?

Jan 22, 2011 7:13 PM ET

Edited Jan 23, 2011 6:50 AM ET.

Response to Joe Chalat
by Martin Holladay

I always thought cap nails were sufficient.

Tyvek literature includes the following information:
"DuPont Tyvek can be installed using a variety of fasteners depending on the application. To attach DuPont Tyvek to wood, insulated sheathing board or exterior gypsum board, use nails with plastic washer heads, such as DuPont Tyvek Wrap Caps. You may choose to use wide staples with a minimum 1” crown."

Elsewhere, Tyvek lists the following possible fasteners:
"• DuPont Tyvek Wrap Cap nails
• DuPont Tyvek Wrap Cap screws
• DuPont Tyvek Wrap Cap Staples for Stinger
• 1.0 inch minimum crown staples (except when installing DuPont Tyvek over foam sheathing)."

Once your siding (or rainscreen strapping plus siding) is installed, the Tyvek isn't going anywhere, so an argument can be made that the Tyvek fasteners only need to be sufficient to keep the Tyvek secured until the siding is on. However, some builders worry that wind pressure can cause Tyvek to "pump" and "belly" back and forth when the Tyvek is installed adjacent to a rainscreen cavity, and that this back-and-forth pumping may weaken the Tyvek over time.

It's unclear whether to worry about his possibility -- we need more research.

Jan 23, 2011 4:35 PM ET

The best tech products since the personal puter
by aj builder, Upstate NY Zone 6a

For readers who know very little about building materials I would like to say;

Zip sheathing is a miracle product that is an order of magnitude better than plain old OSB. Use it instead of OSB if you were going to use OSB.


Delta-Dry, though I have not used it, looks like it too is a miracle product for use in wet humid climates and with stucco and brick and stone siding.

The two products I mention are High Tech Green products.

Low Tech Natural alternatives are available such as rough sawn board sheathing covered with Felt. Is felt natural? Well it is made with the crap leftover from high tech processing so it is not but at least it is not high up on the evil list of products.

Martin, We need to organize this site soon. Natural Green and High Tech Green are two distinctly different topics with distinctly different solutions though someday they may collide.

Jan 26, 2011 3:21 PM ET

WRB and Flashings
by Glen

Great article. I believe there is little performance difference (subject to some special conditions, "cedar" siding, etc and some marketing) between felt and plastic housewraps, the issue of flashing is not discussed. The majority of water intrusions issues do not happen in the field but at corners, openings, penetrations, etc and that is where I see the real benefit of the plastic housewraps. Most of the plastic housewraps having a broad range of self-adhering flashings for almost any condition.

Felt also tears easily, which makes the installation even more important. With an ever decreasing intelligence in the field (as well as in the office), having a product that assists in bridging this gap has some benefits.

At stucco, I almost always see (Texas) 2 layers of Fortifiber's jumbo tex building paper. Maybe the contractors think it was designed for Texas, jumbo and tex in the same sentence:).

In the end, a great product poorly installed isn't any better than a poor product properly installed.

Jan 26, 2011 3:43 PM ET

Response to John Linck
by Jim Dorval

I recently completed a home with exterior polyiscyanurate foam (foil facers both sides) walls and roof.
The roofing is also steel snap-loc.
I still have good cel phone reception inside.
As an aside, my builder used peel & stick for all joints and window flashings.

Jan 26, 2011 3:48 PM ET

Cement board?
by ChrisV

I realize this is off-topic, but I'd like to know whether a WRB behind cementboard siding, without a rainscreen, leads to moisture buildup on the backside of the siding, and if this compromises the integrity of the cementboard. The only answer I've gotten so far is, "nobody puts in rainscreens around here, and there haven't been problems yet."

Jan 26, 2011 3:49 PM ET

DC14 Drainage Mat
by Robert Car

Excellent discussion so far.

As an option, does anybody have any experience with this Pactiv product? It is not a WRB, as it needs one behind, but it does offer a way to ventilate behind cladding. And it costs about $0.375 per per sq/ft.

I'm considering using it instead of furring strips, and I'll be interested in any opinions you might have.

Jan 26, 2011 3:51 PM ET

Response to Chris V
by Martin Holladay

All types of siding dry faster if there is a ventilated rainscreen gap between the siding and the sheathing.

Fiber-cement siding is less susceptible to rot and peeling paint than wood siding, however, which is why fiber-cement siding is often installed without a rainscreen.

Jan 26, 2011 4:02 PM ET

WRB's air barriers etc.
by TC Feick

Thank You, Martin.
This is good stuff, and it does not get enough attention. As was stated, Zip does provide a good air barrier as well as a WRB. We have been involved with builders who use Zip and who have used OSB in the past. Blower door tests on both types of houses, pre drywall, confirmed.

Your comment "Plastic housewraps are rarely used under stucco. " unfortunately is not correct in the Philadelphia market and mid Atlantic, where products like Dupont Tyvek or StuccoWrap are commonly used. Sadly, we have the failures in this market too. The WRB may not always be the culprit, but it often is not up to the task it is in place to perform.

I'm glad Carl Seville clarified the proper application for Delta Dry as a ventilated rainscreen. I talked with these guys at IBS and I like their product for its intended use. Homeslicker plus Typar is an interesting product, if the budget allows, also.

So, how do we incentivize 15# felt manufacturers to improve the quality of a commodity product? Articles like this may just let the genie out of the bottle, if code officials read it.

Jan 26, 2011 4:28 PM ET

by Greg

I just read in your comments that tyvek is susceptible to uv deterioration. Is this true and if not how long since the problem has been corrected. ? This is in reference to some building additions with no siding and just tyvek for 2-3yrs. ( i am a building inspector)

Jan 26, 2011 4:37 PM ET

Edited Jan 26, 2011 4:38 PM ET.

Response to Greg
by Martin Holladay

When installed in accordance with the manufacturer's instructions, Tyvek will not suffer any UV degradation. According to the manufacturer, "DuPont suggests that Tyvek be covered within four months (120 days) of installation." (See ).

If Tyvek has been left exposed to the weather for 2 to 3 years, all bets are off. The builder has failed to follow the manufacturer's installation recommendations, and that's a code violation.

Jan 26, 2011 6:11 PM ET

Adding to Martin's response to Chris V
by Michael T Heffron

I have heard by way of one of Dr. Joe's seminars that cement board siding should be considered a resevoir cladding which means it will hold moisture and that moisture can be driven into the wall due to solar exposure. Therefore a drainage space whether stapping or homeslicker or what have you should be used. My two cents to a great blog.

Jan 26, 2011 6:15 PM ET

Response to Michael
by Martin Holladay

I agree -- a rainscreen gap goes a long way to reducing the chance of inward solar vapor drive. For more ways to limit inward solar vapor drive, see When Sunshine Drives Moisture Into Walls.

Jan 26, 2011 6:20 PM ET

by Andrew

Great article on WRB's, I have read alot on this topic and your writing is clear and descriptive. On a recent remodeling job I debated using 30# felt as a lo-tech "green", non-tyvek solution, with a modest perm rating; but I recalled experiences with felt from the past; course, bulky, heavy, tears when you don't want it to, hot in the sun, stiff, sticky, lays flat until it gets wet and fish mouths all over the place, etc. On the other end there are any number of partially completed buildings in my area that have tyvek flapped to shreds after one season.

On a trip to the lumber yard I stumbled on GAF Deck Armor, a blue colored roof underlayment. I checked it out on the web and discovered it had a perm of 16 and when I made a cup out of it, it held water indefinitely. I bought a 1000 sf roll for a little under $200. I was suprised a how light the material was, the rolls are 54" wide weighing less than 40 pounds. It appears to be a thin plastic film, laminated between two layers of spun fabric. While it is intended for roofs and a proprietary GAF slate system, it worked beautifully on exterior walls, it was tough, when fastened with standard 1/2" type arrow staples it was secured very well. I was not looking for an air barrier so I just lapped it 3" horizontally and 6" vertically. It comes with a 2" grid for easy measuring and cutting. It fit inside and outside corners snuggly and multiple layers don't bulk up under strapping or siding. I have several areas on the building that have gone unfinished for 2 years and the material still looks like new. The areas I have finished I used a ship lap siding with a 1/4" plywood strapping for a capillary break. I was skeptical of the extra labor of building in the rain screen but after deciding I didn't need 3/4" of space and working out flashing details with windows, doors and Deck Armor the process went smoothly. I added a screened vent at the bottom and left a space at the top for air flow behind a barge board.

Jan 30, 2011 1:31 PM ET

Tyvek is dead to me ... And I'll tell you why!
by Michael

We have been using zip system since 2008 and won't go back. It all comes down to installation of the product vs many of the other WRBs. Tyvek is a nightmare to put on and if done incorrectly will fail. The other nice part of zip system is that we can easily apply felt paper to it and moist stop for brick etc. I haven't jumped on board with the zip system roofing product yet based on it's very high cost, but love the advantech 1 1/8" osb flooring.

As for the concerns that the tape will fail, I trust the people at huber ... having tried to remove it within a few days of installing it, I believe in it's longevity.

Apr 2, 2011 1:26 PM ET

Garage Rehab Problem(s)
by Marvin Oosterbaan

To Martin Holladay: Are you available for consulation?

Apr 2, 2011 3:51 PM ET

Response to Marvin Oosterbaan
by Martin Holladay

In general, I have a full-time job that doesn't leave time for moonlighting. But I'll do my best to provide advice if you have a question, which can either be posted here or sent to me: martin [at] greenbuildingadvisor [dot] com.

Jun 19, 2012 5:07 PM ET

Liquid-WRB + paint for OSB shed
by Phil Burman

Hi Martin,
I have built an OSB-sheathed storage shed, whilch I plan to finish in something weather-proof, but don't need insulation etc. The barn-style doors allow lots of ventilation. My plan is to use a liquid-applied WRB (likely StoGuard EmeraldCoat or GoldCoat), and paint over that directly with exterior house paint. I understand this is not conventional, but I think this should work to protect the OSB & frame. What are your thoughts? I'm keen to save on the time & expense of using stucco over mesh etc. Any comments are welcome. Thanks very much

Jun 19, 2012 5:21 PM ET

Edited Jun 19, 2012 5:22 PM ET.

Response to Phil Burman
by Martin Holladay

I can't recommend your suggested approach. Paint is not siding. No manufacturer of liquid-applied WRB would approve of your plan.

Liquid-applied WRBs need to be protected by siding after no more than 4 months of weather exposure. What's going to happen to your WRB when your paint starts to peel?

Jul 28, 2012 3:34 PM ET

Twist on the "How long can Tyvek be exposed" question
by Ray Clark

All questions about "How long can Tyvek be exposed" that I have seen have been from the perspective of someone who intended to use it as-is whenever they got around to covering it.

I have a couple of walls covered with Tyvek, and I fully plan to take it off and put on new when I get there. It has been up for ten months, and I am wondering if it will remain an adequate water / rain barrier for another year or two until I can get the job done, then put on new Tyvek and side. Or do I need to replace it every year I delay?

It is very well fastened (Cleats mostly, some cap nails) and is not going anywhere unless it disintegrates. I just don't want that to happen between November and March!

It is in upstate NY. Thanks.

Jul 28, 2012 4:20 PM ET

Response to Ray Clark
by Martin Holladay

This is a question that is best answered with common sense. If winter is approaching, inspect the Tyvek before the weather gets too brutal. Is it fraying? Coming loose around the fasteners? Showing signs of transparency? If so, replace it.

If it looks good, leave it.

Jul 29, 2012 9:58 PM ET

I was thinking that as the
by Ray Clark

I was thinking that as the sunlight broke it down that it would get weaker, and at some point under stress it would suddenly rip. Of course there is alot of stress when there are high winds in the winter, and if it went then it would be difficult to repair, so sometime around September/October I need to make a judgement as to whether or not it is going to make it. Although there are no guarantees, I was hoping that there were some anecdotal experiences, like "Mine was fine for X years" or "Mine failed after X years" or "After X years it looses its strength and easily rips". Yes, I certainly will look at it, but I would think that it would be weakened too much long before it was apparent, so I was hoping that I could get some experiences to weigh with my observation.

Nov 25, 2012 3:13 AM ET

Combining Housewrap and Asphalt felt?
by Rod Jarboe

My company is a manufacturer of synthetic faux stone panels and we are evaulating our installation instructions for 2013. We would like to know if it makes any sense to recommend a combination of a waterproofing felt and a house wrap for more confidence in keeping water out in case water gets through the interlocking panel seams.. We understand that another option might be a drainage system, but drainage systems are more expensive than asphalt sheets (and yes the drainage system provides a different function).

Nov 25, 2012 7:11 AM ET

Edited Nov 25, 2012 7:37 AM ET.

Response to Rod Jarboe
by Martin Holladay

First of all, I hope that your company has good insurance. Right now, I believe that there are more construction-defect lawsuits arising from faux-stone veneer than any other cladding. (To see some photos of the types of problems that end up in court, see All About Wall Rot.)

Here's my prediction: any manufacturer of faux-stone panels that does not recommend the use of a ventilated air gap between their cladding and the wall sheathing will be bankrupt within a few years.

Frankly, it's a little scary that a manufacturer would seek advice on this website. I strongly urge you to spend a few thousand dollars hiring a consultant from the Building Science Corporation to develop your installation manual. It will be an excellent investment that, over the next few years, will save you thousands of dollars in settlement fees.

I notice from Linked In that your company is Replications Unlimited. A few of the statements in your brochures raise red flags:

which requires several stages and specialized stone mason's labor to install, URESTONE panels installs easily and quickly with screws and/or adhesives . The only tools required are a drill (used as a screw-driver) and any wood type saw for trimming to exact fit. Anyone that knows how to use these simple tools can easily install several hundred square feet in a day!"

Nov 25, 2012 11:48 AM ET

Faux Stone question
by Rod Jarboe

Thanks for your response and appreciate your thoughts. - Regarding exterior applications - our company focuses on Metal building and Modualr building applications that are over exisitng exterior systems. Regarding projects outside this area - i am not totally in the loop but management is aware of the issues with the EFIS system and has addressed surface preparation systems prior to adding the faux stone system. After coming accross your article - just was curious if there were any other options - got the message.

Nov 28, 2012 6:17 PM ET

Moisture damage
by Todd Noice

I'm a General Contractor in the Pacific Northwest and I specialize in rot repairs. I have contended for the past 6 years that if you have a home built with OSB, a WRB and vinyl windows and it faces south you have a problem. If you are frustrated with the lack of information, the conflicts and inconsistencies in manufacturer installation instructions and the lack of solutions or the high cost of screen systems you are not alone. Close scrutiny of expert advise from engineers with little or no bloody hands experience in the forensics of rot damage reveals there is a lack of cohesive advise on solving moisture rot problems. My situation is unique in that I take care of 111 homes in a condo association and I see a tremendous amount of product failures, installation errors and maintenance issues. The use of primed white wood trim, Masonite, Hardie siding and vinyl windows exacerbates the problem of moisture rot as well. The solution is early detection and correction and ideally a meticulously installed screen and siding system. Bring your money. I have attempted to illustrate what I see with my website. I have also tried to get as many manufacturer representatives on site as I can but they are in the sales volume business not bloody hands on constructive advise business.

Dec 25, 2014 11:47 PM ET

felt paper with strips for ventilation
by Tristan Roberts

When all is said and done I remain intrigued by felt paper as an inexpensive, effective, time-tested WRB.

One thing I would like to see felt paper improve on is the rainscreen issue. Let's say I feel that furring strips are overkill as far as a rainscreen for my climate and specific project location. But as a nod to rainscreens I'm looking at a textured housewrap like Hydrogap.

I was just reviewing some and there is a recommendation to install 2" strips of felt paper over studs to provide a bit of ventilation behind the clapboards. This seems like a low-cost, low-fuss way to get the best of both worlds. I am not familiar with this practice but I get the impression that it's been around.

What do you think—Martin or others? Thanks.

Dec 26, 2014 6:31 AM ET

Edited Dec 26, 2014 6:40 AM ET.

Response to Tristan Roberts
by Martin Holladay

A variety of materials can be used to create an air gap between the back of the siding and the WRB or sheathing. Many builders use the trick you are talking about -- installing vertical strips of folded-over asphalt felt to create a small air gap. The vertical strips are usually installed over a continuous layer of asphalt felt, although there is no reason why the strips couldn't be installed over plastic housewrap.

I wrote about this approach in an article called "Another Rainscreen Tip." The article was published in the March 2007 issue of Energy Design Update. In that article, I wrote:

"The latest tip for creating an airspace between siding and the water-resistive barrier (WRB) is simple and inexpensive: install vertical strips of folded-over asphalt felt every 16 or 24 inches on center. Depending on the choice of asphalt felt (#15 or #30) and the number of folds, a variety of thicknesses can be created; in fact, by varying the strip thickness, the strips can be used as shims to correct minor framing irregularities.

"According to Troy Sprout of Hendersonville, Tennessee, the method has many advantages. It’s ‘a simple, fast and efficient means to mark the studs over the housewrap,’ he notes. ‘The system prevents the siding from bowing over random button-caps [housewrap nails], and maintains an air gap/drainage plane to prevent the paint from being forced off the siding.’

"Sprout is a fan of asphalt felt. ‘I prefer felt as a sheathing wrap to any of the newer woven products,’ he says. ‘I’ve witnessed it still doing its job after 50 years behind brick. I even use it under modern housewraps when a building inspector will only accept the modern plastic wraps. It is inexpensive, durable, easy for one person to install and, most importantly, very effective at preventing water damage to the framing.’ "

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