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Old 05-01-2014, 09:16 AM   #16
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How to keep a detached garage comfortable


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Originally Posted by cleveman View Post
I had built a lot of garages and never finished the inside of one. I built a couple of 24x24's with hip roofs like yours, 4/12 roofs. I went ahead and insulated the walls with r-11 or 13, I don't remember which, and sheetrocked the walls. I built them with 2x8 ceiling joists 2' on center and I sheetrocked the ceiling as well, no insulation. I figured I could always blow it in later. One of them I insulated a bit with some r-11 which I gutted out of a basement elsewhere.

For about $400 in sheetrock and insulation, it makes a helluva difference in summer and winter.
cleveman- Thanks for the reply. Hip roof....never knew what it was called, but I have learned to hate it. Any reason why the pitch of the roof is so shallow? I hate going in the attic in the main house because there is no room to move around....I've got more room in the crawl space under the house compared to what I have in the attic.

I wish that I had added insulation to the walls before I put them up. It sounds like blowing insulation in after the fact may be my only option, although it doesn't sound like that would work very well due to the voids/settling that would occur over time. Any other suggestions?

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Old 05-01-2014, 09:19 AM   #17
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How to keep a detached garage comfortable


ddawg16- Thanks for the explanation. I'll take a look at that, and see how hard that would be. I finally had a high enough post count to view the link to your garage build....all I can say is very impressive. I would love to do something like that to my garage, and eventually the main house. That would be really nice.....
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Old 05-02-2014, 12:46 AM   #18
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How to keep a detached garage comfortable


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Once you have the ceiling joists in...hang 5/8" drywall. You don't need to insulate....not in LB.

Next....you need airflow....you need to make some soffett vents on the outside so air can enter the now enclosed attic and go out the roof vent you have or will add.
ddawg16- I was reading through your 2nd story addition thread.....very impressive again....although I don't think that you should call yourself a DIYer....all of the stuff that I saw was better than some of the tradesmen that I've paid to do work.

Your comment about not needing insulation in LB....is that because of the weather, or a city code? Just curious....

I don't have a soffit on the outside. The roof over hangs the walls, and the rafters can be seen extending about a foot and a half from the wall. The 1x6 boards that make up the roof can also be seen. On the house, there are rectangular cut outs in the walls that can be seen from inside the attic. So the exterior wall basically extends up to the roof. I assume that I would have to put some sort of hole here to allow the attic to draw air in.

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Old 05-02-2014, 05:04 PM   #19
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How to keep a detached garage comfortable


The weather....excluding this week

It sounds like you already haves soffett vents. Can you take pics? If they are....that is half the battle.
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Old 05-02-2014, 06:04 PM   #20
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How to keep a detached garage comfortable


No soffit vents on the garage. I do have them on the house. This is a pic of the garage.

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Old 05-02-2014, 08:33 PM   #21
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How to keep a detached garage comfortable


Here's a pic of the vents I have on the house. The garage is a detached garage.
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Old 05-03-2014, 12:06 AM   #22
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I agree with most of the posts on page 1, insulate at the ceiling or insulate just below the roof. Without ceiling insulation you are doing zip against the heat flux gain from above. Without insulating the walls you will be hot, minimum code for your area is R-30 ceiling, R-13 walls; http://energycode.pnl.gov/EnergyCode...ate=California

Granted this is for living space, not garages, but it would be foolish to add ceiling/wall drywall without a thermal barrier to keep the heat out, IMO. Radiant barriers work well if your insulation values are below code and AC ducts are in attic; http://www.inspectapedia.com/Energy/...t_Barriers.htm

Expect a reduction of the asphalt shingle life by 10%, same as for an unvented attic; http://www.buildingscience.com/docum...on?full_view=1

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Old 05-03-2014, 12:07 AM   #23
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No soffit vents on the garage. I do have them on the house. This is a pic of the garage.

Can you take a pic inside of the top plate where the rafters sit?

You might want to cut some slots in the stucco for vents like your house. That will do wonders for ventilation
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Old 05-03-2014, 12:25 AM   #24
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Can you take a pic inside of the top plate where the rafters sit?

You might want to cut some slots in the stucco for vents like your house. That will do wonders for ventilation
I'll see if I can get some pics of the top plate tomorrow. I was thinking about cutting some vents in the stucco to add to the ventilation.

I did some research on the web for the type of vents that I had the roofing company install on the roof. The website for Ohagen vents had a calculator for intake/exhaust vent requirements. I put in the square footage of the garage, and it looks like I need to add more vents. The website suggested two vents high, and two vents low on the roof. I have two vents total, and I would consider them both on the high side of the roof. I've e-mailed the roofing company, but haven't heard back from them.

Thanks.


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Old 05-03-2014, 12:34 AM   #25
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Originally Posted by Gary in WA View Post
I agree with most of the posts on page 1, insulate at the ceiling or insulate just below the roof. Without ceiling insulation you are doing zip against the heat flux gain from above. Without insulating the walls you will be hot, minimum code for your area is R-30 ceiling, R-13 walls; http://energycode.pnl.gov/EnergyCode...ate=California

Granted this is for living space, not garages, but it would be foolish to add ceiling/wall drywall without a thermal barrier to keep the heat out, IMO. Radiant barriers work well if your insulation values are below code and AC ducts are in attic; http://www.inspectapedia.com/Energy/...t_Barriers.htm

Expect a reduction of the asphalt shingle life by 10%, same as for an unvented attic; http://www.buildingscience.com/docum...on?full_view=1

Gary
Gary-

Thanks for the reply, and all of the links. I've been looking through them, and learning a lot about roof ventilation. Looks like I really blew it when I added drywall to the walls without any insulation. It would be a real job to remove work benches and shelves that I've mounted on the walls in order to pull the drywall to add the insulation. Would it be worth all of the extra work?

I was looking more at adding radiant barrier to the roof deck, even though most of the people that have commented on this thread advise against it. I have checked with the GAF website (they make the roof shingles that I have), and they state that the shingles would still be covered by their lifetime warranty if I applied radiant barrier to the roof deck. It would be a lot of work for me to add the rafters and skin the ceiling of the garage, so the radiant barrier would be easier to install. The other issue is that the roof is so shallow that the "attic" that would result from adding the rafters and drywall would only be about 2 1/2 feet high, at the highest point.


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Old 05-03-2014, 10:54 PM   #26
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Here are a couple of shots of the top plate.


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Old 05-03-2014, 11:51 PM   #27
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So use some foil-faced foam board after furring the rafters down to make up the required R-value after ventilation, OR forget venting, use ff FB directly against the roof sheathing boards, with canned foam at perimeter; R-5 (1") required, check with local AHJ; http://www.buildingscience.com/docum...rchterm=attic+ ask when using it on garage door; may not require an ignition barrier as plain blue/pink foam board would.

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Old 05-04-2014, 12:45 AM   #28
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So use some foil-faced foam board after furring the rafters down to make up the required R-value after ventilation, OR forget venting, use ff FB directly against the roof sheathing boards, with canned foam at perimeter; R-5 (1") required, check with local AHJ; http://www.buildingscience.com/docum...rchterm=attic+ ask when using it on garage door; may not require an ignition barrier as plain blue/pink foam board would.

Gary
Gary- Thanks again for the reply....as well as the link to more information. Those really come in handy.

In looking through the link, with the roof on my garage, I think that I would have to go with the non-vented option. Reason being is that I don't have any soffit vents on the existing roof, so there would be nothing to feed the air gap between the foam board and the roof deck. In reading through the article, it looks like the best bet for me would be as follows:

Get the 1" foil faced foam board, and install it in between the rafters directly to the roof deck. I would use expanding foam sealant at the gaps between the foam board and the rafters. Hopefully, I've got that right. If that is the case, I'll probably wait for the weather to cool down a little before I try to tackle this project. Thanks again for all of the information you provided.
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Old 07-03-2014, 02:26 PM   #29
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Do you really want to be super heating the sheathing and roofing material [with a radiant barrier]. If it's shingles it would really shorten the life.
Testing done by the Florida Solar Energy Center has shown that roof shingle temperatures increase between 5 and 10F when radiant barriers are installed under the roof decking. They found that the color of the asphalt shingles had more affect on shingle temperatures than the use of a radiant barrier.

"Other tests comparing white and black shingles have shown that shingle color makes a greater difference in peak shingle temperature than the presence or absence of attic ventilation or an attic radiant barrier system. These tests, accomplished at the FSEC flexible roof facility, showed peak temperatures for black shingles (solar absorptance of 97%) to be almost 25F hotter than peak temperatures for white shingles (solar absorptance of 76%). Thus, if elevated temperatures can result in composition shingle failure, then the problems are likely to be much more pronounced for darker shingle products, especially in climates with large quantities of solar radiation like the desert southwest."

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