I have an attic converted to a bedroom and the crawlspace is insulated with rock wool between the joists and foam board (isolofoam) with a rating of R10.1 covered with gyproc over that. The knee wall has fibreglass between the studs.
I had a leak caused by ice damming this winter and was told by a roofing specialist that the rock wool and isolofoam should be removed because it is preventing airflow from the soffit.
Can the isolofoam and gyproc be reinstalled on the knee wall over the fibreglass?
Replies
Do you mean the joists (slope with the roofline) or the rafters (flat)?
In order to see if it is a good idea to put the foam on the outside of your kneewall, you would have to calculate what the net temperature would end up at the inside surface, considering the thickness of the fiberglass and of your foam, using your location.
Yes, I meant the existing rock wool is between the rafters with the isolofoam and gyproc on top of that.
Do you know if the rafter treatment continues over your converted attic bedroom?
If so, it might be that removing rafter insulation from the space outside the kneewall would only move your ice dam problem further up the roof.
I have no idea what is above the ceiling of the converted attic bedroom. There is no access.
Does the wall of the bedroom slope part of the way up?
In other words, does the rockwool/foam/gyproc sandwich continue to form part of the interior wall/ceiling of the bedroom? Or does the wall go all the way up to a right angle connection to the flat ceiling?
Yes above the knee wall it slopes upward until it meets the ceiling. I assume that the rafters behind the slope in the bedroom has the rock wool insulation which appears to be the original insulation when it was just an attic. I added the isolofoam and gyproc over the exposed portion of the rafters to increase the R value but apparently that just compounded the problem of the existing rock wool blocking the soffit air flow.
Where did the ice dam form and leak into the house?
The problem is not just air flow.
it is heat loss to the bottom of the roof deck, that melts snow cover, except the roof further down is not getting heated, so that water that melts over the heated part of the house re-freezes when it hits the part of the roof that covers the overhang and soffit. Then water behind the dam looks for a way through the shingles if such a way is lower than the path over the ice below.
You might want to get a second opinion before tearing into a removal project.