Is it worth it to install rigid insulation on the inside face of framing?
I have a small, 1910 home in Seattle. This year, we will be gutting most of the main foor and installing recycled cotton batt insulation in the 2x4 wall cavities. Would it be worth the extra effort to install rigid foam on the inside face of the framing before installing a vapor barrier and drywall? ( I've read that there can be some concern about rigid on the interior and creating a cooler environment for the framing and thus making it more susceptible to moisture issues.) We completely restored the exterior of the house last year (cedar beveled siding over sheathing) so installing rigid on the exterior is unfortunately not an option. We also replaced all the windows and sealed the nooks and crannies so the interior treatment is our last line of defense against tighting up our house.
Thanks!
Asked by Anonymous
Posted Thu, 03/18/2010 - 16:36
Posted Thu, 03/18/2010 - 16:36
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You may want to think about 2x horizontal strapping on the inside of the studs. This will help reduce thermal bridging and give you an extra 1.5 inches of insulation for the wall cavities. Net, and blow in some nice cellulose insulation. Avoid using batts. Airtight Drywall Approach and a vapor retarder finish paint (avoid poly vapor barriers) will keep the moisture laden air from getting to the cold exterior sheathing and condensing.
You will loose a weeee bit of interior space, but its worth the added efficiency.
Posted Thu, 03/18/2010 - 17:33
Lauren,
Yes, it's worth it. Adding foam on the interior definitely addresses thermal bridging through studs and improves the R-value of the wall. Because you're worried about condensation in your wall, it makes sense to pay particular attention to air sealing at penetrations, at electrical boxes (buy airtight electrical boxes), and at the top and bottom plates (use gaskets or caulk under the drywall at these locations).
Posted Thu, 03/18/2010 - 18:31
"Is it worth it?" has many dimensions and as many answers.
You want to improve the thermal efficiency of the house and have chosen a natural, recycled, low-embodied energy insulation material. So it is understandable that you might question the addition of petrochemical foam insulation as contrary to your "green" goals.
As Brett suggested, there are other alternatives which are greener than foam and more effective than cotton batts in the stud cavities. Adding 1½" horizontal strapping and blowing cellulose will eliminate most of the thermal bridging, increase the whole wall R-value, better fill the cavities than batts can do, and allow the thermal envelope to breathe (and dry) in both directions, which is important in a wet climate like yours. Do not use a polyethylene vapor barrier, as it will eliminate drying potential to the interior. Use a latex vapor retarder primer, instead.
And do, as Martin suggests, seal all air leakage points, as that is critical to a durable structure.
Posted Thu, 03/18/2010 - 18:49