Cleaning out attic in older 1954 rancher, original batt insulation badly damaged due to moisture (no leaks, but previous owners replaced roof in the winter) and rodents. Attic is vented via soffit vents all around, and original insulation went right to the wall top plate, so access to the edges is difficult from inside the attic.

There is no vapour barrier in place, and I'm trying to decide between re-insulating with fibreglass batt or rigid foam. We plan on interior reno including replacing the ceilings somewhere in the next 1-3 years, and I'd like to re-use whichever insulation I use now.

My contractor friend thinks there will be no issue putting down fibreglass batts without a vapour barrier for a couple years. Several others have recommended cutting up poly and using tuck tape to put a vapour barrier between the ceiling joists, and then putting in batts. I'm not sure how effective this would actually be, and it's also a pretty tedious and time consuming idea.

A local company is selling recycled polyisocyanurate sheets. Using R5.6/in for older polyiso, the cost to insulate to >R20 (single layer of 4" polyiso or R20 batts) comes out to about 1400CAD, and >R40 comes out to 2900CAD for batts, 2800CAD for polyiso. Drywall to cover the polyiso is about 700-1200CAD depending on type.

I'm leaning towards putting down 1-2 layers of polyiso, taping the seams, and covering with drywall. The cost difference isn't huge and the performance and ease of installation look better. Is this a good plan, or should I stick with the fibreglass batts?

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