Insulation for attic conversion with 2×4 framing
Jsobo
| Posted in Energy Efficiency and Durability on
We are converting our attic to living space and I am looking for input on the best way to insulate the space. The home is in Portland, Oregon and there is limited room for insulation because the roof is framed with 2×4 rafters (picture attached) and we can’t fur out the space due to ceiling height. I was considering using closed cell spray foam either alone, or in combination with some other form of insulation. Any suggestions would be greatly appreciated.
Thanks,
Joe
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Replies
Joe,
You are in Climate Zone 4C. According to the 2012 IRC, the minimum R-value for roofs and ceilings in your climate is R-49.
Q. "I am looking for input on the best way to insulate the space."
A. The best way to insulate this space is to put almost all of the required insulation above the roof sheathing. This method requires installing one or more layers of rigid foam above the roof sheathing, followed by a second layer of roof sheathing and new roofing.
Q. "Any suggestions would be greatly appreciated."
A. The 3.5 space between your rafter bays provides room for about R-13 of air-permeable insulation (fiber insulation) or about R-19 of closed-cell spray foam. In either case, the actual R-value of the roof assembly will be less due to thermal bridging through the rafters. That's not much, but it's the best you'll be able to get if you are unwilling to install rigid foam above your roof sheathing.