Sealing Screw Penetrations Through Water-Resistive Barrier
curiousgreenzebra
| Posted in Green Building Techniques on
Hello,
We are using a house-wrap WRB like ProClima Mento/Fronta, exterior insulation and a rain screen, with HeadLok structural screws to fasten the battens onto the house.
I don’t see much of people talking about sealing the screw penetrations through the WRB. Is this not an issue because the screw hole is air and/or water tight? I see for the roofs there are products like Tescon Naideck https://foursevenfive.com/tescon-naideck/ to deal with penetrations but I don’t see anything for the walls.
Thanks for your thoughts.
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Replies
I found a few comments that relate to your question and might be helpful in this Q&A thread:
https://www.greenbuildingadvisor.com/article/all-about-water-resistive-barriers
Most notably:
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.
Kiley,
Thanks a lot for your comment and link to that thread! I've read that and will continue researching.
Kiley,
I also found
https://www.greenbuildingadvisor.com/question/airtight-sheathing-sealing-nail-penetrations
which is asking a similar question, although not about the exterior insulation.
Is there any value in angling the screws such that they direct water outward?
Jon,
I think it would depend on the exterior insulation material. If you are using foam as an exterior insulation, capillary action will probably negate any benefit of angling screws up. Mineral wool is a different story. However, angling screws up is beneficial from structural performance of the rain screen assembly.
In general, a screw penetration isn't much of a hole as long as the screw is intact. It would become a hole if you backed the screw out completely.
Beyond that general point, you have to look at where that screw winds up in the total assembly and how much water could possibly hit it. My house has thousands of nails holding the shingles on, but only a handfull are actually exposed. None of them have or will see an appreciable amount of moisture.
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