Attic insulation over attached garage


Old 02-09-03, 07:52 PM
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Attic insulation over attached garage

I would like to know if it would be beneficial to insulate the attic over an attached garage. Here are some specifics:

- new one story house
- attached two-car garage (facing south)
- uninsulated metal overhead door
- currently uninsulated
- house attic and garage attic are shared
- climate - highs of 100's and lows of mid-20's
- location - Houston, Texas
- rest of the attic is insulated with r30 plus blown in fiberglass over that

What do the experts say?
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Old 02-10-03, 07:21 AM
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There is basically no energy saving from insulating between two unconditioned spaces, ex. attic and garage and/or garage and outside. There is a savings for insulation between the garage and the house.

Though there may not be any cost effectiveness to insulating a garage, there is such a thing as comfort. This is considered a value which differs from one person to another. For example, if one was to use the garage for other things, like a work shop, this would more than justify the insulating of the garage. Even though no savings are experienced. However you must balance the cost of doing so with the increased comfort. For example, adding R-13 to the walls and ceiling would increase the comfort in the garage, but adding R-30 would not create that much of a difference from the R-13 installation, yet it would cost you more. This is because the insulation is going between two unconditioned spaces. The same applies to a vapor barrier in this application, there would be no need for one because both are unconditioned spaces, yet the vapor barrier is an additional cost to installation. On the other hand, if using encapsulated insulation makes it easier for you to install, it may be worth purchasing for you. There are other reasons why one might insulate an unconditioned garage, but it would not be to save money nor energy.
Old 02-10-03, 08:54 PM
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If you use a high efficiency insulation such as radiant barrier (RB) material, it could reduce the amount of heat to and from the walls facing the garage. This is because FG is about 10% eff and RB about 97% eff. The RB will not condensate moisture either. If you want details on how to install let me know thru e-mail. You can also install bubble foil over the garage door. That makes a big difference.

You might want to look into installing a RB over the attic insulation too. That could reduce your a/c bills up to 30%.

Thank you for considering my opinion.
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