# How to keep a detached garage comfortable



## joecaption (Nov 30, 2011)

If you want cooler going to have to insulate those walls and ceiling and sheetrock.
Really need a ridge vent so the whole roof gets vented and soffit vents.
Without a real ceiling with insulation over it, it's always going to be hot in there.
Would have been better of adding foam insulation to the door not a radiant barrier.
That whole door acts like a solar panel.


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## propman07 (Dec 13, 2011)

joecaption said:


> If you want cooler going to have to insulate those walls and ceiling and sheetrock.
> Really need a ridge vent so the whole roof gets vented and soffit vents.
> Without a real ceiling with insulation over it, it's always going to be hot in there.
> Would have been better of adding foam insulation to the door not a radiant barrier.
> That whole door acts like a solar panel.


joecaption- Thanks for the reply. So it sounds like I need to start looking into insulating the sheetrock on the walls. I was looking at blowing some insulation into the walls. Is that something that you think would work?

As far as a real ceiling, I'm not sure what you mean. Do you think that I should put up some insulation on the roof, then cover it with drywall?

I found a bunch of online kits for the garage door, which is why I decided to give it a try. I guess that I should have posted the question here first, before I did all of the work. What kind of foam are you talking about for the garage door? Is that something that I could install over the radiant barrier, or should I pull the radiant barrier off the door, and go with the foam?

One of the roofing companies that I got an estimate from suggested that I install the radiant barrier on the roof. Is that something that I should look at doing as well?

Thanks for the help.


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## joecaption (Nov 30, 2011)

A whole lot cheaper to just add rafters, insulate then sheetrock.
Got a picture of the roof and where a ceiling would be if there was one.
Not a fan of trying to blow insulation into a wall like that. You always end up with voids because your work blind, and it tends to settle leaving gaps.
Also never did see the point of a radiant barrier. Do you really want to be super heating the sheathing and roofing material. If it's shingles it would really shorten the life.
Really do not need some expensive kit to insulate the door. Some 1/2 blue foam and some construction adhesive made just for foam is all you need.


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## propman07 (Dec 13, 2011)

joecaption said:


> A whole lot cheaper to just add rafters, insulate then sheetrock.
> Got a picture of the roof and where a ceiling would be if there was one.
> Not a fan of trying to blow insulation into a wall like that. You always end up with voids because your work blind, and it tends to settle leaving gaps.
> Also never did see the point of a radiant barrier. Do you really want to be super heating the sheathing and roofing material. If it's shingles it would really shorten the life.
> Really do not need some expensive kit to insulate the door. Some 1/2 blue foam and some construction adhesive made just for foam is all you need.


I'll take a picture later today, and post it so that you can see what the roof looks like. Due to the shallow pitch of the roof, there isn't going to be much of an "attic" if I put a ceiling in.

Sounds like I should have thought about adding insulation to the walls before I hung the sheetrock. Hindsight...20/20....

Didn't think that the radiant barrier would be heating the roof materials, but that makes sense. The heat would go through the roof and radiate into the cavity. The radiant barrier claims only to re-radiate 5% of the long wave radiation, but it sounds like that might still be too much.

I may look into the blue foam idea. I don't know if the Boss would be okay with the inside of the garage door being blue, so hopefully, I will be able to find some blue foam that is backed with white/silver instead of the blue.

It was unusually hot yesterday, but I did notice that it took longer for the garage to cool off. I am assuming that the foil backed barrier that I added to the door trapped the heat in the garage, instead of letting it radiate out through the door. Pretty much the opposite effect of what I was shooting for.

Thanks again for the info.


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## propman07 (Dec 13, 2011)

Here are some cell pics of the roof. In the first one, you can see the opening for the passive vent that the roofing company installed. It is very close to the ridge of the roof.

The second pic shows the top of the garage door where the roof starts to pitch up to the ridge.

I've looked at other homes in my area, and on most of the detached garages, the roof pitches up to the ridge from either the font/back walls, or the two side walls. On my garage, the roof pitches up from all four walls to the ridge.


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## joecaption (Nov 30, 2011)

A vent that low does little to remove any moisture or heat.


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## taylorjm (Apr 11, 2013)

Seems like you are going to have to add something to create an attic space and insulate the garage from the attic, otherwise it's going to be a sauna.


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## propman07 (Dec 13, 2011)

Taylorjm Thanks. Any recommendations? False suspended ceiling? Drywall?


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## taylorjm (Apr 11, 2013)

It's hard to say from the pics. I think you are going to have to drywall, or wood sheeting of some type, or pretty much anything that will allow you to put some insulation in the attic side to keep the heat up high.


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## ddawg16 (Aug 15, 2011)

Wow....flashback.....

Your garage is what I 'used' to have.

I'm not far from you so I know exactly what your dealing with. You have half the battle done...walls have drywall.

Click on the link in my signature regarding the garage....I would not be surprised if the same builder built both our garages....

Those 1x6's that are like an X in your ceiling....take them out. They were put in to keep the walls square while the built the garage.

You are going to need a lot more ceiling joists. What you have now is really nothing more than what they call rafter ties. Basically, the 2x4's you have going across are keeping the walls from pushing out. 

If your garage is like mine was, it's more like 18.5' wide. According to my LA County building PDF, your span would require 2x6's 12OC...or 2x8's 16"OC. Me? get a bunch of 2x6's 20' long...cut to length and nail them in 12" OC. As you work your way down, you can sister up to the existing 2x4's. Don't take those out..they are nailed in to your top plate pretty good and provide good rafter tie support.

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.


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## cleveman (Dec 17, 2011)

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.


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## propman07 (Dec 13, 2011)

joecaption said:


> A vent that low does little to remove any moisture or heat.


The vents are actually pretty close to the ridge...probably within two feet or so. I'll see if I can find a pic of the outside of the roof for reference.


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## propman07 (Dec 13, 2011)

ddawg16 said:


> If your garage is like mine was, it's more like 18.5' wide. According to my LA County building PDF, your span would require 2x6's 12OC...or 2x8's 16"OC. Me? get a bunch of 2x6's 20' long...cut to length and nail them in 12" OC. As you work your way down, you can sister up to the existing 2x4's. Don't take those out..they are nailed in to your top plate pretty good and provide good rafter tie support.


ddawg16- Thanks for the reply. If I add the 2x6 like you are suggesting, how do I attach them to the top plate near the wall? I think that the top of the 2x6 would hit the underside of the roof near the wall edge.


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## ddawg16 (Aug 15, 2011)

Look at your existing 2x4's....you will see they cut the end at an angle...

You most likely have a 4:12 pitch (if like mine was). So you cut the end at that angle and push it up in there to sit on the top plate.

Normally this is done with no roof so you can get proper nailing....well....your roof is in the way...but you still want to put blocking between joists....and if you have an air nailer....you should be able to get some nails into the block at an angle.


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## propman07 (Dec 13, 2011)

cleveman said:


> 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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## propman07 (Dec 13, 2011)

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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## propman07 (Dec 13, 2011)

ddawg16 said:


> 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.

Thanks.


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## ddawg16 (Aug 15, 2011)

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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## propman07 (Dec 13, 2011)

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


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## propman07 (Dec 13, 2011)

Here's a pic of the vents I have on the house. The garage is a detached garage.


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## Gary in WA (Mar 11, 2009)

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/EnergyCodeReqs/?state=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/Radiant_Barriers.htm 

Expect a reduction of the asphalt shingle life by 10%, same as for an unvented attic; http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?full_view=1

Gary


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## ddawg16 (Aug 15, 2011)

propman07 said:


> 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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## propman07 (Dec 13, 2011)

ddawg16 said:


> 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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## propman07 (Dec 13, 2011)

Gary in WA said:


> 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/EnergyCodeReqs/?state=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/Radiant_Barriers.htm
> 
> ...


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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## propman07 (Dec 13, 2011)

Here are a couple of shots of the top plate.


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## Gary in WA (Mar 11, 2009)

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/docu.../irc-faq-conditioned-attics?searchterm=attic+ ask when using it on garage door; may not require an ignition barrier as plain blue/pink foam board would.

Gary


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## propman07 (Dec 13, 2011)

Gary in WA said:


> 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/docu.../irc-faq-conditioned-attics?searchterm=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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## RadiantGUARD (Jul 2, 2014)

joecaption said:


> 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 10°F 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 25°F 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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