What kind of insulation board should I use?
Browncow32
| Posted in General Questions on
I Live in a cold Climate 6A. I live in a cape style house with 2×4 Knee walls, that have batt insulation falling down on the unconditioned side. I want to put insulation board as an air barrier and to add R-value. What kind of insulation board do you recommend and what thickness?
Thanks,
Mark
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Replies
Mark,
Q. "What kind of insulation board do you recommend?"
A. Any kind of rigid insulation -- EPS, XPS, or polyisocyanurate -- will work fine. However, polyisocyanurate is the most environmentally friendly option.
Q. "And what thickness?"
A. The thicker the better. I would start with at least 2 inches of polyiso. If you want to install 4 inches, you won't regret it. Pay attention to air sealing when installing the polyiso.
You'll also need to be sure that there is blocking between the floor joists under the kneewall, and between the rafters above the kneewall. These details can be tricky to install, so you may conclude that it's easier to move the thermal boundary to the sloping roof. More information here: Two ways to insulate attic kneewalls.
Thanks! Also my house is a modular home and the Knee wall floors have house wrap underneath the floor joist holding the insulation up . The house wrap is falling down,creating a big air leak and nearly impossible to seal it back up from the attic side. I don't want to cut the dry wall from underneath to get to it either(i think that would be more work than its worth to try and save the tattered house wrap). would it be better to bypass the hose wrap and put polyiso inside the bottom each joist cavitiy, seal it and put the insulation back on top of the polyiso?
Mark,
I don't know what you mean by the "knee wall floors." If you mean the floor of the small triangular attic behind the kneewall, this floor is usually over conditioned space in a typical Cape. In other words, the room under the attic is heated and includes a finished ceiling. I don't know what you mean when you write that there is "housewrap holding the insulation up."