Interior Continuous Insulation
Has anybody used or see any issues with using Rockwool Comfortboard80 on the interior surface of a house?
I’m renovating a 100+ year old balloon framed house with interior 1” board sheathing, true 2×4 studs, an additional layer of 1” ship lap siding, and a brick veneer.
My approach is the following: insulation the stud cavities with blown in cellulose, install Intello Plus over the interior board sheathing, then install a layer of Rockwool Comfortboard 80 with 2×2 strapping. Following all this with a layer of 5/8” Type X drywall.
Does anyone see issues with installing the Comfortboard 80 INSIDE the house even though it’s meant for outside? Any advice is greatly appreciated. Thanks!
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We used similar wall construction for a commercial project, zone 7A. See pics. It was a very efficient envelope, about 9000 sq/ft. The thermal reflective surface was the vapour barrier. All services were run in the warm cavity, leaving very few envelope penetrations.
Air sealing your envelope will be difficult, so the Intelo will be your best bet if not removing the interior 1" ship lap. Your wall will dry very easily to the outside and having that thermal break will make a big difference. You may want to run all your electrical in that warm cavity (using 2x3 furring) to further reduce penetrations and air leakage. 2x3 will give you depth for electrical boxes.
In a fire, the Roksul will perform vastly better than foam!
My 90’s house has 1” interior polyiso. It is a PIA installing trim, hanging pictures, etc. I don’t recommend it personally.
If you're running furring every 16", it's no different really vs stud walls. For anything not hitting a stud, I use the "E-Z Ancor" self drilling anchors which are excellent for drywall, regardless of wall type.
Interior continuous is seldom discussed here, but I can tell you that in a zone 7A building (winter temps exceed -35 C) the building project I mentioned had a smaller actual measured heat load at 9000 sq/ft than my 1800 sq/ft (old, but retrofitted) home. For a building with an exterior that is not touched during a retrofit, CI makes a lot of sense, particularly if you can give up some interior space. Rim joists at retrofit can be a challenge for interior CI, however targeted spray foam was prescribed and worked well in the commercial project. We also did an insulated slab over-pour (gave up about 4" interior height) which was quite simple to tie into the interior CI. In other words, it was pretty easy at the slab level to get a complete thermal break, carried to the wall CI.
The biggest downside of interior CI is that you're giving up about 5" of interior floor space on exterior walls. It also does not address thermal bridging at rim joists which would be addressed with exterior CI.