Insulating a 5/12 scissor truss system
A builder is building the shell (dried in, with siding) and I’m increasing the insulation and air tightness.
The rear rooms in the house have vaulted ceilings, with a 5/12 roof and 2½/12 ceiling.
The builder doesn’t usually build with raised heel trusses and so the quoted price was high.
As a note, I can not fathom how to blow cellulose on the back side (away from the larger attic) of a scissor truss attic once the sheetrock is covering the ceiling. For this reason, I was going to sheath the vaulted ceiling with osb and create an air barrier before the sheetrock goes in. I will blow cellulose in phases as I sheath off the ceiling.
Anyhow, there is still going to be scant insulation for at least 2′ as the trusses get really shallow as they approach their bearing.
My idea is to install 3″ of polyiso to the ceiling, extending 36″ up the vaulted ceiling. Install 1/2″ battens over (under) the polyiso and screwed into the trusses. Fur the remaining ceiling down with 2x4s on edge (countersunk screws into trusses).
This set up still doesn’t give me R49 to the edge but it does give me R29 aged at the minimum instead of R14.
The great room wall is inset 24″ from the other wall. Both are shown together in the drawing.
Is this a reasonable, second-best solution to the cold edge problem?
[Chrome and Firefox keep crashing when I try to attach the picture. I’ll post it when I can.]