Update to 1910 Duplex in 4a mixed climate attic insulation search
The search continues for a company that will do best practices for insulating my attic! It is a walkup attic (with stairs) with zero insulation, unvented, with two small windows in dormers. Balloon frame, stucco duplex.
To recap, I had one company that started out recommending 5 inches open cell foam against roof decking, told me to do my own air sealing with can foam ahead of time (despite fact that there is a big hole at soffit, like bigger than my fist, and my arms aren’t long enough to reach there). They also recommended closed cell foam at party wall in attic. Even though I use my attic for storage, they said they wouldn’t need to do intumescent paint unless I’m trying to sell soon (i.e. I wouldn’t get caught for violating building code).
Next company wanted cellulose in the 9″ gap between floorboards and plaster ceiling, but said they had no plan for the stairwell in attic that would be affordable.
Asked first company to bid on 2 inches of closed cell foam against roof decking (planning for flash and batt as Dana recommended).
Another company bid on 2 inches of closed cell foam.
The company that came today does do air sealing (hurrah) and did a blower door test. At negative 50, my numbers hovered around 5200… this is about 1300 sq feet, not counting attic and basement.
They also recommended open cell foam at roof decking, but recommended baffles above. Claimed 5 inches of open cell foam was ‘effective R38’. I said that’s not possible because of the R-value per inch of open cell foam. Estimator also claimed no one does closed cell foam in attic, only in basement and crawlspaces because of its water blocking properties. He googled his company’s comparison of kinds of insulation and it showed open cell foam is 3.7/inch. Oops. Then he was trying to say ‘it depends on the pressure of how you blow it in’… I’m like yeah, that’s the difference between open cell and closed cell.
This has been quite a journey!
I don’t know yet what this company is going to charge for air sealing attic walls/soffit/around chimney (They already charged $150 for blower test) but I think I’m going to have to go with them for air sealing, then another company for closed cell foam then install the batts ourselves. (Found out the other side of the duplex has fiberglass batts at their roof decking, so it seems like I can get away with not dealing with party wall)
I’m curious how bad the 5200 number is… any perspective there?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part