Insulating attic with pitched roof


Old 06-28-20, 09:22 AM
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Insulating attic with pitched roof

Hello everyone, were in the process of remodeling a 1908 craftsman style home. The upstairs has finished space, but has peaked ceiling due to the roof line. The roof structure is made up of true 2x4. We will need to insulate the 2x4 cavities at the roof up until it gets to ceiling height where we created an attic space that will be filled with blown in insulation.

I know to meet code we will need a minimum of r-30 insulation. The problem is we only have a 2x4 space to fill, so fibreglass batts are off the table. I know that there will need to be air flow between the eaves of the roof and the attic space to prevent moisture.

I heard that you can use spray foam insulation to insulate the underside of the roof to prevent moisture. Would the same be true if I were to use 2" foam board, cut to fit the 2x4 bays then sealed really well at all edges and seams?

If that were to be viable, I would use 3 layers of 2" foam board to get the desired r-30. I know this will cause me to loose 2" of space, but it's the right way to do it.
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