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Garage Roof Insulation

 
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Old 08-11-2015, 01:18 PM   #1
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Garage Roof Insulation


I am going to insulate my garage roof because I don't want a ceiling and want to keep the extra space open. I wanted to do closed cell spray foam but thought that would present a problem if I ever have to install a new roof having the foam stuck to the chip board. Next I was thinking craft faced fiberglass rolls with a foam board for extra insulation and support for the batts. I was also pondering radiant barrier under the fiberglass insulation.

I don't have any sofet vents and only have a bird cage on the roof whitch I would remove and seal because I am going to AC and heat the garage.

What are your thoughts on the best way to get the max out of this project.
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Old 08-11-2015, 01:29 PM   #2
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Re: Garage Roof Insulation


What do you mean by "bird cage?"

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Old 08-11-2015, 03:26 PM   #3
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Re: Garage Roof Insulation


The turbine vent.
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Old 08-11-2015, 08:58 PM   #4
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Re: Garage Roof Insulation


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... I wanted to do closed cell spray foam but thought that would present a problem if I ever have to install a new roof having the foam stuck to the chip board...
Replacing whatever roofing material used wouldn't be an issue. Are you concerned about some day replacing the decking?
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Old 08-11-2015, 09:33 PM   #5
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Re: Garage Roof Insulation


Yes. I don't want to spray foam up there and have it stick to the decking and get firm up if it needs to be replaced. So was thinking of fiberglass rolls and foam board.
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Old 08-15-2015, 05:04 PM   #6
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Re: Garage Roof Insulation


Where is the home and how about a picture of the inside and exterior?
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Old 08-15-2015, 10:14 PM   #7
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Re: Garage Roof Insulation


So if I understand right, you want to do a "hot roof"?

Since it sounds like you will have no venting
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Old 08-17-2015, 07:07 AM   #8
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Re: Garage Roof Insulation


Yes no venting. Like a cathedral ceiling but instead of sheetrock I pained on using foam board.
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Old 08-17-2015, 07:19 AM   #9
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Re: Garage Roof Insulation


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Yes no venting. Like a cathedral ceiling but instead of sheetrock I pained on using foam board.

Since your roof is probably not air sealed and your finished roof is already on, you are pretty much stuck with doing spray foam. That is my opinion. Closed cell, you could flash and batt. I'd use closed cell and then open cell or dense pack cellulose to finish off the interior. Foam board under the rafters helps with thermal bridging, but it is labor intensive and you still need to install gypsum or ply over foam board for fire code issues.
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Old 08-17-2015, 07:21 AM   #10
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Re: Garage Roof Insulation


Ok. Thanks a bunch.
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Old 08-18-2015, 08:18 AM   #11
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Re: Garage Roof Insulation


Where is the home?

If you are demoing the interior, you have a few options.

SPF is definitely the easiest but isn't cheap. Depending on where you are, OC SPF will work fine too.
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Old 08-18-2015, 05:03 PM   #12
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Re: Garage Roof Insulation


Houston TX. Not demoing. The garage was never finished out.
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Old 08-20-2015, 07:02 AM   #13
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Re: Garage Roof Insulation


Is the roof metal or asphalt? South Facing? Pitch?

You spray a roof in Texas and you can count on it lasting not as long. You can create a below deck vent system or spray it.

If you spray it, I would still put in some rigid foam to to isolate it from the roof deck.
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Old 08-20-2015, 09:43 AM   #14
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Re: Garage Roof Insulation


That's good info thanks.
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Old 08-20-2015, 09:44 AM   #15
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Re: Garage Roof Insulation


The roof is pitched on all four sides. Front is east facing.
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Old 08-22-2015, 10:05 AM   #16
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Re: Garage Roof Insulation


If it were my home, I would create a below deck vent channel with some foil faced ISO board, open the roof at the bottom and the top, and then spray over the foam.

Best of both worlds. Insulation and venting.
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Old 08-22-2015, 01:39 PM   #17
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Re: Garage Roof Insulation


That sounds like a really good idea

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