GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

roof insulation retrofit

raul4817| Posted inGeneral Questionson

A good friend of mine is having his roof redone soon and would to insulate it. The assembly from seems to be 2×6 ceiling joists with 2×8? rafters above that.

What we know..
A few rafters need to be replaced or sistered accordingly.
2×6 ceiling joist + spacing between joist and rafter + 2×8? possible rafters
4通风开口,2北side and 2 on the southside.

Since he will be replacing the sheathing we will have unrestricted access to the ceiling below.

My original plan was to box out can lights and purchase a spray foam kit and air seal and spray 2 inches topside of the drywall then blow in cellulose or rockwool up to vents.

option 2 was to caulk and spray foam all cracks and gaps in addition to boxing out cans, assuming drywall is a sufficient air barrier with proper sealing topside. blow in insulation in the same manner.

option 3 would be to blow in insulation up to top of 2×6 then staple down an air barrier such as intello plus or 6 mil poly. Followed by some more blow in insulation up to vent openings.

All 3 would be superior to what he has now. I remember reading here that cellulose is a pretty good air barrier on its own with ample amounts. I this plausible just blow in 10-20 inches and call it a day?

Also the vent opening seem a bit frugal to me. For proper air flow and to truly keep this a cold roof will I need to add a few more?

Just preliminary thoughts but eager to hear from the community on this one.

Btw we are in chicago climate zone 5

Raul

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |