Adding insulation while roof being replaced in a Cape Cod
We have a Cape Cod style home in Zone 5 and I’d like to add some insulation while the roof is being replaced. We had continuous soffits installed, air baffles and blown in insulation in the attic (up from R30 to R49). The second story attic has two main rooms with tall knee walls, one is 6′ the other is 8′. The roof is sloped 8/12 and there is a bit of a short cathedral ceiling of about 3-4 feet long in the room with the 6′ knee walls to the ridge. There is some fiberglass insulation stuffed into the bottom of the knee wall/cathedral but I don’t believe it goes all the way to the top.
With the new roof, I was going to have a ridge vent installed and with the roof off, thought we could peel back some of the roof decking where the knee wall/cathedral ceiling is and install some insulation and air baffles to channel air up and out the ridge vent.
In addition to the knee wall section, there is the section where the stairs go up to the second floor. There are two rafters, one has no insulation in it, the other has some R13 in it. That stair section is the worst though. Typically in the winter, the snow melts off quite readily. (see first pic)
Second pic is a side view of the 6′ knee wall after I installed house wrap for air sealing and keeping the fiberglass wall insulation in place.
The third pic is the top of the vertical chase and the open bay next to the stairs. Talk about air leakage!
The roof rafters are 2×6’s on 16″ centers…
1) Install 4″ of rigid foam (foamular) in the rafter bays, using spray foam (Great stuff) to air seal and hold in place. I can get an R20 that way and still have a 1 1/2″ of an air channel to the newly installed ridge vent. Another benefit, the rigid foam will create a nice air barrier at the bottom of the rafter and along the sides.
2) Fiberglass batts slightly compressed to add air baffles to create the venting. Should get close to R19. Will need to additional air sealing.
3) At least for the stairs section, could fix from the inside. Remove drywall and could even lower the ceiling slightly to get some more insulation.
As much as I’d like to get R49 up there in the rafter bays, R20 is going to be about as good as it gets. Not ideal, but better than the nothing I have now.
Option 1 is my preferred choice, but is there anything that I”m missing or another option not listed? Any watch outs for Option 1?
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