installing foam insulation on exterior
user-152671
| Posted in Energy, Heating & Insulation on
Have a home just north of Toronto that was constructed in the early 70’s. Was very poorly insulated and has no vapour barrier, other than craft paper that faces one side of fiberglass bats. We are considering the addition of 1″ foam board insulation and house wrap to the exterior of the building, after which we will re-side. I am concerned that moisture from the interior will end up on the inside face of the foam board. Should I be? Short of removing the drywall and installing a vapour barrier, are there any other ways to tighten up the envelope. I’ve heard that painted surfaces in effect are like a vapour barrier. Is this true? Thanks.
Replies
Using 1" rigid on the outside there will be no reason to use a house wrap. What ever brand foam you use will sell tape to seal all the joints and this becomes your rain screen. You should have a vented space between the siding and the rigid foam. You can use furring strips made out of treated plywood, !/2" rigid foam, or Homeslicker (http://www.benjaminobdyke.com). Back-prime your siding. The rigid foam should prevent any condensation from happening inside the wall. Your going to want to get your windows installed on the outside of the 1 " foam. Keeping moisture out of the wall from the inside will be your biggest challenge in an existing home. Since most moisture will get into the wall through air movement sealing all penetrations on the inside and outside and putting a good semi-permable latex paint on the inside will be your best bet. Now that you have your house sealed up tight with the taped rigid foam on the outside you now have to address indoor air quality, consult your local HVAC contractor. Also go to http://www.buildingscience.com, http://www.eeba.org.