Taping insulated sheathing vs. housewrap
Usesolar
| Posted in Energy, Heating & Insulation on
In a remodel I have going, I plan on using foil-faced closed cell sheathing (on top of 5/8 waferboard), and then taping all joints for my air barrier. I plan on using the airtight drywall method for keeping moisture out of wall cavities. I assume I wouldn’t need to use a housewrap (such as Tyvek). Is this a correct assumption? Are there downsides to this strategy, or is this just a little more labor intensive?
Replies
Welcome to Breaktime.
The answer to your question depends very much on your location.
There have been several recent discussions about similar insulation methods. If you try the search function at the top of the page, you will enjoy several days of reading on your topic.
Look down a few posts in the Energy, Heating & Insulation subforum to this one:
http://forums.taunton.com/tp-breaktime/messages?msg=110319.1
Alfie was asking somewhat the same question.
Short answer to the air barrier question: if you think the taping won't peel off over time, then the foam is ok as an air barrier, in place of a wrap. Pay attention to other places air can leak into the house, such as under the sill, between sheathing and framing, etc. Use a sealant like Tremco accoustical ("black death" - keep it off your hands if you want any afterhours attention during the following week).
Pay more attention to the water vapor issue. General rule: retard moisture from moving into the wall cavity, but don't trap it in there when it gets in during upset conditions. Foam by itself is ok in a 1" layer outside, given that you plan on keeping inside air from leaking into the cavity, but I'd avoid anything with a foil facing in a heating climate.
I've assumed you are in a heating climate, but are you? Fill in your profile.
Thanks for the response, Dick. I am in central Kansas, and we have about 4800 heating degree days, and 1600 cooling degree days, so heating is the primary concern. My main concern with this system was locking moisture in the wall cavity, since foil backed polyisocyanurate is not very gas permeable. The question about longevity of tape is also a great one...probably will have to wrestle with that as well! I'll check out the other references--looks like a lot of info and opinions have already been posted. Ken
In theory, you don't need the tyvek, however, in a similar project that I just completed, I installed a layer of tyvek over the foam. This is primarily a drainage plane to which I could tape the window flanges (and have go over my head flashings). The tyvek also helps to protect the top edges of foam panels.
I've had OK luck getting tape to stick to foil. Have tried numerous kinds of tape, most of it works most of the time, but it seems that all of it fails at least occasionally.