The need for vapor retarder on inside of 2 x 6 wall in Frisco CO (cold climate)
I’m doing major energy retrofit for existing townhouse in Frisco CO. I’m considering insulation and air sealing options with HRV. The code calls for installation of a “continuous vapor retarder” on the conditioned side of all insulation in exterior walls ….. I am considering using open cell foam for the cavity. We have noticed water damage from the exterior in a number of locations and are considering residing. If we pursue residing, I’m considering 2″ of unfaced XPS under the siding, but I’m worried that if I install interior vapor retarder, the wall won’t breath to the inside, and the XPS will limit breathing to the outside,possibly causing condensation difficulties. I have read Builder’s Guide to Cold Climates and it seems to indicate no retarder, beyond the painted drywall is necessary. Do you have any recommendations for properly insulating this wall so it is airtight, warm and without vapor condensation issues?
Thanks
Chet
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Replies
Do as you plan and use a latex vapor retarder primer (several major paint companies offer this) on all the interior surfaces of the thermal envelope. That should meet code and still allow some drying to the interior.
Of course, seal all penetrations into the thermal envelope, use point-source exhaust fans in kitchen, laundry and baths, and ventilate at a rate to maintain no more than 40% indoor relative humidity during the heating season.