Updating house insulation
Foil-faced polyisocyanurate is almost impermeable to water vapor; a 1-in.-thick foil-faced board has a permeance of 0.05 perm. Pentane does not damage the earth’s ozone layer, although it may contribute to smog. Tape the foam seams and seal the perimeter of each piece of foam with caulk, high-quality tape, or canned spray foam.While polyisocyanurate was formerly manufactured using HCFCs as blowing agents, U. Once this rigid foam air barrier is secured and sealed, the stud bays can be insulated normally.The main disadvantage of this approach is that the felt is not an effective air barrier.But if you end up installing spray foam, that's not a problem, because the spray foam is your air barrier.The advantage of thick rigid foam is that it reduces the chance of condensation or moisture accumulation on the interior side of the foam.
The air barrier can be on the exterior, the interior of the assembly, or both..
There are two possible ways to approach this worry.
The conservative approach (assuming that most of the stud bay will be filled with air-permeable insulation) is to make sure that the rigid foam meets the minimum recommendations mandated by code for this type of assembly.
(For more information on this issue, see Calculating the Minimum Thickness of Rigid Foam Sheathing.) Another (less conservative) approach is to use relatively thin unfaced Expanded polystyrene.
Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. Its vapor permeability is higher and its R-value lower than XPS insulation.