unfaced Polyiso insulation under sheet rock
user-7515395
| Posted in Energy, Heating & Insulation on
I’m in the middle of a deep rehab for an 1890’s home. We went down to the studs and padded them out to 5 1/2″. From the outside in we will use Hardiboard clapboards, Hydrogap for the spacer, 7/16″ taped Zip system over the original 1″ board sheathing. For insulation we plan to use high density blown in cellulose between the studs and then 1″ unfaced polyiso sheeting directly under the sheetrock to reduce thermal bridging.
Any comments or suggestions? (Spray foam is not an option, this is an historic structure)
Replies
Greenbuildingadvisor.com would be a better place for your question and learning.
I would want a TRUE RAINSCREEN vs the hydrogap. Hydrogap is a good product for a housewrap though.
Thanks RussMill,
I have posted a similar question on Greenbuildingadvisor.com and hope to hear some comments from that site as well.
The rain screen is a new concept for me and, as such, is a late addition to the wall program. We are limited by the existing roof overhang so cannot add much to the exterior walls without causing a new problem. The Hydrogap was the only product I found that would function as a rainscreen and add a scant 1/8" to the wall.
Thats what im pointing out its NOT a rainscreen. 1/4 inch plywood can even be used for the rainscreen and not cause much problem with trim, etc.
What you have described is almost exactly the way I handled the walls for the 1820's Cape that I renovated. Unfortunately my project was some years ago when building science was a just starting to evolve. I used clapboards over Tyvek (no rain gap) and for a couple reasons did not use any panel type sheathing over the original 1" boards. Cellulose in the 'stud' space behind the plaster lathe (minus the plaster) which I left in place. Over this I put 1 1/2" polyiso and sheetrock.
I wanted to preserve the lathe in place for any future historic reference, which assumes the wall would be returned to a plaster finish. For me the main problem was both budget and time, plus working alone. My interest in preservation was often in conflict with the reality of making a place to live in somewhat comfortably. If I did it again I would have polyiso on the outside over Zip system plus a rainscreen. Also, lots of attention to air tightness. Then I could return the interior to a more historically accurate look. But that would mean a lot more work detailing the outside so it never happened. The house was comfortable to a degree, but the lack of careful attention to air infiltration was a big mistake.
It's good to hear that I am not alone in my thinking. As someone with an historic preservation background I have to applaud your work to preserve the original plaster by encapsulating it. I would have thought that the polyiso and cellulose would have made for a fairly tight home, even without extra air sealing, but air sealing seems to get a lot of attention these days.
Can I assume that there were no problems with the polyiso sheeting? Did the sheet rock go over the polyiso sheeting easily? Any undo compression or dimpling? Any suggestions or recommendations?
Thank you for your reply