Low slope shed roof design and insulation
I have a project that we are considering using this roof design. It would be a monopitch shed style roof sloping towards the south at 1/2:12 pitch with 2′ overhangs. I’m scratching my head at how you would detail and insulate a roof like this. Minimum R49 requirement
-Is there a code compliant dense packed option? Using I joists for the roof I could go 14″ which would meet the requirements for my climate zone 6. Does ventilating above the roof deck count? This roof would be wrapped with a air/vapor permeable barrier all the way around.
-If rigid foam is used above the roof deck, does it extend even with the overhangs? If deeper i joists are used below can you just insulate the top half of the joist so the rigid/fluffy ratio stays in line?
-Can you omit rigid foam entirely and frame a perpendicular insulated i joist assembly on top of the roof deck? For example, membrane-sheathing- 11 7/8″ i joist assembly with densed packed cellulose-air sealed sheathing-11 7/8″ i joist assembly with fiberglass batts.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part