Sealing cedar wall shingles and air infiltration
Hi. I’m building a house in CA and it’s a craftsman style, and will be using some double dipped cedar shingles as the siding. My GC is planning on using Tyvek as a house wrap, and then a second layer of asphalt saturated paper on top of the Tyvek and nailing the shingles to that. I think it’s planniong on galvanized or steel nails to fastening the shingles
I am worried about all those holes causing a problem with air infiltration through the sides of the house. Is that a problem?
My GC has done a fair number of high end homes here with this 2 layer approach and never had a problem with water infiltration or rot (we don’t get a ton of rain here in 94062), but didn’t know the answer on the air infiltration issue.
thanks!
mike
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Replies
Milo, the nails or staples holding the shingles on do a very good job of sealing the holes they make, so while there is probably increased infiltration, it would take very precise equipment to be able to measure it. In other words, don't worry about it.
I'm curious about the two-layer approach. It won't hurt anything, but I've only done that or seen it done when the WRB has been exposed too long. I wonder if your GC is worried about an old concern about tannins affecting the housewrap, which is no longer an issue, or if they do a lot of masonry-clad homes where two layers is needed? It's good practice to space the shingles off the housewrap with a rainscreen of some sort (Homeslicker Classic is the most common) but in a dry climate it's not as important.
Yes, I think the tannin issue is/was a concern. He is using double dipped shingles painted at the factory and 2-ply paper, he likes the overkill approach as he really wants to avoid water problems on the exterior.
He even uses two layers of materials on the windows to make sure it's a super durable seal.
What is your air barrier(s)? Taped plywood, OSB or a fully adhered film as an air barrier will be better than a loose film like Tyvek.
Consider Typar (over Tyvek) for permeability and tannin reasons.
https://www.greenbuildingadvisor.com/community/forum/green-building-techniques/16146/building-felt-vs-house-wrap-white-cedar-sidewall