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This post is prompted by an interesting 9 page article in JLC on “sheathing wrap “(8/2000 p. 79). They used the term “sheathing wrap” to include asphalt felt, gradeD building paper (common in Western USA), and plastic housewrap – either perforated or non-perforated (woven). The article contained some interesting points that I felt some of you would like to hear…

The article says that it is difficult to compare the performance of the various sheathing wrap products, partially based on the fact that there is no standard testing practice. It goes on to say that studies have proven that the moisture content of the sheathing on a wrapped house is less than that of an unwrapped house – regardless of what type of wrap is used.

The article also says that many folks don’t realize it but that when siding is nailed flat to the sheathing wrap, you do not really have a drainage plane. This is not a problem with.. oh-oh, here it comes, the V word… vinyl siding as it is not nailed tight (my deduction). Further, since vinyl siding, inherently has airspace between it and the sheathing wrap, and is non-absorbent, siding drying to the inside of the building is not a problem. To answer the need for a drainage plane, some house wrap manufacturers have come up with corrugated housewrap. Another solution is strapping (firing strips).

The article downplays the importance of how permeable the “sheathing wrap” is. Further it says that: “Unfortunately, no one has yet developed a material that has “one way permeance” allowing [water] vapor out but not in.” This statement contradicts a , < Obsolete Link > previous post by one of our more prominent BT contributors that insinuated that housewraps are supposed to provide one way vapor transmission.

Asphalt (roofing) felt: Today’s asphalt felt is a different product than that used a hundred years ago. The original was actually cotton felt – today’s is recycled cardboard. Therefore, I can’t necessarily buy the argument common here at BT – “if asphalt felt has worked for a hundred years, it works for me”. Asphalt felt has the advantage that it becomes more permeable when wet. It is also somewhat absorbent; therefore allowing water trapped between the sheathing and the wrap layer to be wicked out to the exterior when the assembly gets wet. This property enhances the ability of the house to dry out. Also, it seals more effectively around nail & staple penetrations than plastic housewrap.

Grade D Building paper: (which I personally have never used) is often used under stucco but manufacturers say that it can be used under any kind of siding. It is thinner and rots easier than asphalt felt. An advantage to the grade D building paper is that it is less susceptible to degradation due the leaching of various chemicals present in siding such as cedar, redwood and possibly stucco.

The article says that this problem of a deteriorating sheathing wrap (both asphalt felt and plastic housewrap) due to chemicals present in the siding can be largely reversed by backpriming wood and fiber cement products.

Plastic housewraps: 2 categories; perforated and non-perforated (woven) housewraps. Most all are made of either polyethylene polypropylene. Most housewraps are more waterproof than felt/paper products.

Plastic housewraps are rarely used under stucco, because the stucco being in contact with the house wrap yields the wrap no longer water repellant. Also, some housewraps are severely degraded by surfactants present in some stucco.

In summary, I gather what the article is saying is that no paper/felt/housewrap is inherently superior or inferior although some are better for particular applications (siding types). Further, a house that is wrapped is less prone to water damage to the sheathing than one that is not, but that proper flashing and other water infiltration prevention techniques are still essential.