Open-cell foam in an old home
We just purchased an 100+ yr old home that has been updated with new plumbing, wiring, and HVac units. There is a new metal roof on the home. There is an area over one of the bedrooms upstairs that is inaccessible for insulation. The room is hotter than the others. We can get some insulation blown in the area. We are trying to decide between open cell foam for the remaining attic or more regular fiberglass insulation. I’ve read a lot about open cell foam. My concerns are:
1) the area that can’t be accessed. Will this let in moisture and cause a problem
2) there has been some previous chimney leakage and I’m worried about more water problems with the open cell foam
3) There is an HVAC unit in the attic. There isn’t much room to maneuver around and I’m concerned about harming the unit with the foam.
Will you please advise on the best insulation given the circumstances.
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Spray foam contractors need to be able to see the surface that they are spraying the insulation on. You wrote, "There is an area over one of the bedrooms upstairs that is inaccessible for insulation." If it really is inaccessible, spray foam can't be used. Either the ceiling will have to be removed, or the roofing will have to be removed.
In the other attic you describe -- the one where access is tight -- you'll have to discuss the situation with your spray foam contractor. The contractor will tell you whether or not there is enough room to work.
If you have HVAC equipment in the attic, it is very important that you find a way to insulate the sloped roof assembly above the HVAC equipment, so that the HVAC equipment is inside your home's conditioned envelope. The insulation can be installed under the roof sheathing (usually, this means by installing spray foam, although other options are possible) or above the roof sheathing (usually, this means by installing rigid foam; note that this approach requires new roofing). Here are links to two relevant articles:
Keeping Ducts Indoors
Creating a Conditioned Attic
Concerning roof leaks at your chimney: This is a flashing problem. Either the problem has been solved or it hasn't. If you see signs of a leak, call a roofer and get the problem fixed.