Main Roof to Porch Roof Connection w/ Rigid Foam Above Deck
I am working on a new construction (not started) house in GA (zone 3) with a lot of porches around the house, so a very common detail is a 10/12 main roofline intersecting a 3/12 porch roof.
The goal is to have 6″ of polyiso above the roof deck, with the T&G decking exposed beneath in the conditioned 2nd floor area, and open rafters on the porch.
I have the porch rafter connection detail from the architect, and a detail from this site on rigid foam above the deck, but having some trouble thinking of the best way to work the insulation layer where the two rooflines connect.
I am thinking of two alternatives:
Insulation under sistered porch rafters (option 1)
– have the foam continue on the main line, and taper-end into the porch rafters/deck
– run the same insulation along the main rafters (under the porch rafters) from the exterior wall back up to where the porch rafter connects to the main rafter.
– This seems most(ly) continuous, but looks like it would be tricky to sequence the install.
Insulate Runs Over Exterior Wall, Transition Down (option 2)
– continue the insulation out so that it passes the wall, and insulate up the wall to the bottom of the roof deck.
– taper the insulation down past the wall, and add some transition framing to bridge height transition from the 6″ of insulation down to 0” (decking) as quick as possible
– the porch is about 9 feet deep, it is already a 2’4″ drop, so adding 6″ to the drop seems ok
Has anyone put this kind of assembly together before that could offer advice, or have a detail that might show a better solution?
Any advice would be much appreciated. I have attached some sections marked up like a 4 year old, for reference.
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