Questions regarding garage ceiling insulation


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Old 05-04-13, 07:32 PM
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Questions regarding garage ceiling insulation

Hello! Yesterday for the first time I climbed up into the attic and saw that there are loose-filled fiberglass insulation covering the dinning room, living room, the kitchen, and all of the bedrooms (or the rest of the house).. except the garage! Talked to several neighbors and apparently this is common for houses in the area (Austin TX).

Since the attic is open, there is no barrier between the garage and the rest of the house up there, so all of the hot air might just got radiated back down into the garage due to lack of insulation there. I am planning to add Reflextix to the garage door, but seriously thinking of insulating the garage ceiling. Common R-value for house ceiling in Texas is 38, but the reps at HomeDepot recommended me to use unfaced R-13 fiberglass batts. I thought R-13 won't be enough to act as a barrier, as the temperature can easily get up to 140 during the summer? Also, does it matters to use unfaced or faced batts that come with vapor barrier?
 
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Old 05-04-13, 08:59 PM
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Welcome to the forums!

It sounds like you want to make your garage cooler.

The purpose and function of attic floor/living space ceiling insulation isn't to keep heat out of the living space (or the garage), it's to keep heat in. Adding insulation to your garage ceiling will cost you money without improving the situation.

I would build a wall to separate the two attic areas, and provide adequate passive ventilation for each part.

One question. What is
loose-filled fiberglass insulation?
 
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Old 05-04-13, 09:18 PM
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Nash, loose fill fiberglass insulation is just that, chopped fiberglass that is (generally) blown in with a blower as many other types of insulation. I have it in my attic.

nysryus, my garage is exactly the same, very little to no insulation above and the attic is contiguous with the rest of the house. While it hasn't happened yet this year it is common for my garage to be significantly warmer than the living quarters when the hot weather (such as we have in the Pacific Northwest) arrives. Since my garage is purposely not built with regard to air sealing, due to having the furnace and water heater located here, the walls are not insulated either. Unless you are going to insulated the walls and door along with air sealing additional insulation above the ceiling will have little effect. If your furnace and/or fuel-fired water heater are located in the garage you would also need to wall off that area and provide a separate source of combustion and ventilating air.

I seriously doubt that the lack of insulation in the garage ceiling has any effect upon the rest of the house. After all, the attic is usually quite a bit warmer than the outside air, even with adequate ventilation.
 
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Old 05-04-13, 10:38 PM
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Hi Nash, Furd! Thank you for the reply.

The furnace and water heater are located in the garage, and the walls are not insulated. It looks like this will be a major project to get it the entire garage insulated. Hmm, might not worth the money and effort, i supposed. =/

Maybe opening the garage door by a few inches, as well as the small side window, and use a fan to circulate the air would help? The reason is that wife stores her crafting materials in the garage, along with her crafting.painting station. Therefore, she wants it to be cooler so she could work on her hobbies during the summer when she is not working (she is a teacher).
 
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Old 05-05-13, 03:50 AM
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If you do close off the opening between the two, you must still allow it to be accessible, like putting in a door. That is for firefighter access and required by code. Having the same soffit and ridge venting will help dissipate hotter air that accumulates in the garage attic as well.
 
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Old 05-05-13, 04:05 AM
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As stated, I would close off the connection between the house and garage. I believe that is a code requirement for modern construction, fire and CO concerns.

But insulation isn't a bad idea, it does slow the transfer of heat, although I don't like fiberglass in an open application. Hot air can move right through it. I would opt for blown in cellulose or Roxul batts. Not sure what is commonly available in your area.

In the deep south, adding a radiant barrier directly under the roof rafters is frequently used to direct the heat right back to the roof deck and allow it to radiate out into the clouds or be blown away by convection. Anywhere but into your home or garage works. Also, make sure you have sufficient attic ventilation.

Bud
 
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Old 05-05-13, 07:37 PM
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I have talked to several contractors and they have recommended me to fill the walls and the attic of the garage area with blown in, follow with insulating the garage door and one more roof vent.

To seal off the garage and the rest of the house would cost more, so they did not recommended that route.

Now it is up to wife to decide how she wants to go, and how much she is willing to spend.

Thanks everyone for the suggestions and comments!
 
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Old 05-06-13, 03:04 AM
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Check with your local code official to see if a fire barrier between house and garage is required. One of the concerns is Carbon Monoxide (CO) from vehicles running in the garage being able to pass into the house. Pick up a "low level' CO detector for the house.

Bud
 
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Old 05-06-13, 07:52 PM
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Welcome to the forums!

Cooling the garage would require insulating the ceiling from the hot attic air (insulation insulates warm from cold, doesn't matter which side either is on. lol That is why code requires insulation in your hot climate). The ceiling drywall may be enough without extending new material in the attic to the roof peak, check locally- fig.3: http://www.google.com/url?sa=t&rct=j...KscIbQ&cad=rja

To meet local code for a Class 2 vapor retarder; BSI-060: Joe South Assemblies — Building Science Information

The thicker the insulation, the less you need a radiant barrier, #8; A Close Look at Common Energy Claims - Building Science, Energy Efficiency, Energy-Efficient Construction, Energy-Efficient Design, Energy Star, Energy-Efficient Windows, Insulation, Radiant Heating, Building Envelope, Building Performance, Cost-Effe

http://www.mytexasinspector.com/pdf/...heet%20DOE.pdf

Have you thought about a closed roof, if HVAC is in the attic, expect a 10% less service life for asphalt shingles; BSD-149: Unvented Roof Assemblies for All Climates — Building Science Information

Gary
 
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Old 05-07-13, 01:10 AM
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Wow! So much information.

After much discussion with wife, she has decided to move her crafting station into one of the half used bedroom. She thought it would be too much of a trouble to deal with it all. (So now i have to find storage for all my computer parts, miniature models =/..)

However, in the long run, I will still try to get the garage insulated. Probably start by talking to the local code official as Bud has suggested, and see if separating the attic between the garage and living space is ok. Otherwise, starting insulating the garage door, then the walls, and finally the attic.
 
 

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