Open-cell foam with Tyvek?
css1813
| Posted in Green Products and Materials on
Hello:
We will be starting a new home next year. We are located in the mid lower peninsula of Michigan. We are going with the standard 2×6 exterior framed wall, with sheathing, Tyvek, and vinyl siding on top of that. I am pretty much convinced of open cell foam inside the walls.
My question is, using open cell foam is the Tyvek a good idea for the external face of the walls (just under the vinyl siding? Any issues with this?
Thank you.
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Replies
CSS,
There are no issues with using Tyvek as you propose.
Tyvek is a brand of housewrap, and housewrap is the most common type of water-resistive barrier (WRB). A water-resistive barrier is required by building codes and recommended by building scientists. Its purpose is to prevent water that gets past the siding from damaging the sheathing.
For more information on this issue, see All About Water-Resistive Barriers.
The question wasn't asked but...
The middle of the palm of mitt is the cool edge of zone 5, warm edge of zone 6. In zone 5 it'll be fine to use open cell foam cavity fill without interior vapor retarders as long it's back-vented siding such as vinyl, but not with flat-backed siding tight to the Tyvek.
In zone 6 it'll still need a class-II or tighter vapor retarder even WITH vented cladding, unless the sheathing is highly vapor permeable (to water vapor) , or there is sufficient exterior insulating sheathing for dew point control on wood sheathing.
The IRC chapter 7 prescriptives are a good place to start, but not the whole story:
https://up.codes/viewer/utah/irc-2015/chapter/7/wall-covering#R702.7.1
To know which zone you're in, refer to this map:
https://energycode.pnl.gov/EnergyCodeReqs/images/michigan.png
Blue is zone 6, green is zone 5 (purple is zone).
Thank you very much for the replies. I am in zone 5. From what I read in another article here, the internal painted drywall will suffice as the interior vapor barrier?
Very good articles on this site, I have especially found the articles on open vs. closed cell very useful and practical. Thank you for the information.
Jon,
For a lower perm WRB I've found commercial Tyvek works well. It is half the perms of regular Tyvek and much harder to tear - making it easier to install too.
Consider Typar over Tyvek for perms in the "sweet spot". See below for discussion.
https://buildingscience.com/documents/building-science-insights/bsi-061-inward-drive-outward-drying
Maybe also strips of polyiso on the interior side of the studs - or any other design to reduce thermal bridging.