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Tim Ferringer
Attic workspace insulation

I have an attic over a garage that I want to turn into an office/overnight room. The house is inland in San Diego County and temperatures are regularly in the 90’s in the summer. There is no insulation in the roof, the 2x4s are exposed, as is the plywood sheathing, and the temperature in the attic in summer is probably as high, if not higher, than the outdoor temperature. The asphalt shingle roof is probably 5 or 6 years old, and was installed over new ½” thick plywood.
My question is this. Should I install insulation between the beams and then either ½” or 5/8” dry wall over the beams, OR put up foil radiant barrier insulation to reflect the summer heat and then dry wall over the foil?
I plan to heat and air condition the space but I would also like to save on energy costs. To help with this I recently installed two Velux opening skylights with solar blinds to replace the leaky fixed units that were installed when the house was built in 1953.
I would appreciate any and all thoughts of how to proceed.

MLB Construction
Re: Attic workspace insulation

first thing is that i hope you made a mistake by saying that the roof rafters were 2x4's. i'm assuming that they're actually 2x6's or 2x8's at least. if you're looking for the smartest way to insulate the roof for heat and AC, i would recommend closed cell spray foam insulation. a little expensive but it will do the best job for your heating and AC costs.

dj1
Re: Attic workspace insulation

MLB, just a couple of comments: around Southern California there are many older homes with 2x4 rafters, 16" oc and garages are seldom finished.

MLB Construction
Re: Attic workspace insulation

interesting dj.....is that considered to code? never heard of that over here on the east coast.

dj1
Re: Attic workspace insulation

MLB,

It was to code when they were built. I have a few 60-65 yr old rentals with such rafters. These are one story homes, 1400 sf or smaller.

In attached garages, only wall(s) that touches the interior of the house is/are finished. The rest are not, and that's to code.

Back in the 40s and 50s SoCal homes weren't even insulated.

MLB Construction
Re: Attic workspace insulation

i have seen 2x4 roof rafters but they were always the old true 2"x4" lumber. i don't think anything around here has been built like that since the 1800's or very early 1900's

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