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rigdi foam baord and rock wool

mack2000's picture

I have a house in central Massachusetts that hs been insulated with fiberglass insulation which is in bad shape.  I would like to reinsulate the roof rafters (the house is basically an A frame).  The rafters are I joists.  My thought is that i would use 3 1/2 inches of foam board, creating a vent by placing the board over the flanges of the joists and then adding 7" of rock wool insulaton on top of the board.  Looking for thoughts on this plan and whether there should be a vapor barrier?

 

Thanks

Once you've got 3 1/2" inches (post #216141, reply #1 of 3)

Once you've got 3 1/2" inches of foam board in you've reached the point of diminishing returns.  The return in savings for each inch of insulation after that would be close to non-existant. Your money would be much better spent with using spray foam to air seal.

Florida Licensed Building Contractor, 50 years experience in commercial remodeling, new homes, home remodeling and repairs and all types building maintenance.

Unfortuantely would not get (post #216141, reply #2 of 3)

Unfortuantely would not get me to nearly the R-value need in the north

Walk in freezers only have 2 (post #216141, reply #3 of 3)

Walk in freezers only have 2 1/2" to 3" of foam.  Why would your house need more? Without air sealing R value is pointless. 

Florida Licensed Building Contractor, 50 years experience in commercial remodeling, new homes, home remodeling and repairs and all types building maintenance.