# Foam board in uninsulated garage



## hotincali (May 3, 2017)

Hi all,

I live in Central California with a west facing garage. It becomes unbearable in the summer time, as the intense sun beats down on the metal garage doors all afternoon. There is no insulation in the walls or ceiling (I attached a pic of the ceiling). I have decided to at the minimum to install a 1" foam board on the inside of the garage doors. However, I am debating adding foam board in between (or on top of) the rafters as well. Since this is a substantial cost in materials and time, I was hoping to get some opinions here.

1) My mind set is to concentrate on the west facing side of the garage. My initial thought was to blown in some cellulose insulation into the west facing wall (I believe I can access)--but there isn't much wall as the 3 garage doors take up the majority of the real estate. Is this a waste of time/money/effort? remember, I am going to add 1" foam board to the garage doors at a minimum in this project.

2) Going along with the same "attack the west wall" theme, I was considering only putting foam board on the west side of the garage peak, as this gets the brunt of the afternoon sun. What would be better for overall comfort? The west side (1/2 of the garage) insulated with 2" FB or the entire garage insulated with 1" FB? Due to cost constraints, I am leaning towards one or the other.

3) I am debating whether to cut the FB and install between the rafters or use whole sheets and go over the rafters. I know the R value will be better going over the rafters, but since I use the garage attic as storage, I know i will lose quite a bit by going over the rafters. I can be swayed either way at this point.....

4) Anything else I might not be considering or realizing....

Thanks in advance!


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## Windows on Wash (Aug 30, 2011)

How about some pictures? 

There are a handful of things you can do to help mitigate the heat but some of it will depend on how the space is set up.


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## hotincali (May 3, 2017)

I would love to post some pics, but i am having issues. I am using photobucket. Frustrating.


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## concretemasonry (Oct 10, 2006)

The central valley can certainly be very hot in places.

If you have a totally uninsulated garage, any ventilation will keep it down to the outdoor temperatures. Without ventilation all sun on any surface will raise the temperature. Putting in some ventilation (probably vents on the upper end walls or roof vents) will make a difference and get it down to close to the outside temperature without any cooling cost. An ugly "whirly-bird" vent on the roof will suck out some stale air.

Dick


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## Bud9051 (Nov 11, 2015)

It is difficult to speculate what any partial approach will accomplish. 
Here's a test you can do. Assuming you have windows in the garage pick up a large window fan, something like this:
https://www.zoro.com/air-king-windo...gclid=CKTeq-b21NMCFY88gQodXJUC_w&gclsrc=aw.ds
At 2,000 cfm this would exhaust all of the air in a 20,000 cubic foot garage in 10 minutes. This would give you some idea as to how well a good air exchange would work. The whirly bird concrete mentioned is one option and works 24/7 with no electricity.

If you want to install something on the inside, add a foil barrier between and wrapped around those rafters. Once covered 90% of the heat coming in through the roof will not transfer into the garage. 

Check local code requirements for exposed foam board whether they require an ignition barrier, many do.

Bud


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## hotincali (May 3, 2017)

So would a radiant barrier be a better solution than foil faced foam board? For both rafters and garage doors? Certainly the garage door motors would appreciate it...perhaps someone can school me as to the reasons why?

Foamboard
http://www.homedepot.com/p/Thermash...-Rigid-Foam-Insulation-Board-787264/100549260

vs.

Radiant barrier
http://www.homedepot.com/p/Reach-Ba...flective-Attic-Insulation-Roll-3023/203536782

PS--Still trying to get some pics uploaded...


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## Bud9051 (Nov 11, 2015)

The foil faced foam board already has the radiant barrier when installed with the foil surface towards the open space. The added R-value is a benefit albeit at a cost.

The foam board in your link doesn't appear to be rated to be left exposed, needs a 1/2" layer of drywall covering it. Check with your local authority and if they say ok, get a signed statement and save it so when the house sells it won't surface as a problem.

The only foil faced foam board rated to be left exposed that I'm aware of is Dow Thermax. Similar name but certified product. HD may be able to order it in if not in stock. $$$ but 1" is the least expensive size last I checked.

Using just a radiant barrier should help at a much lower cost. In fact, in very hot climates the roof sheathing is available with a foil face on the bottom for just that purpose. How much would be a wild guess.

Bud


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## hotincali (May 3, 2017)

Silly question I am sure, but what is the reasoning behind the foamboard needing the drywall covering?


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## hotincali (May 3, 2017)

https://goo.gl/photos/3ehuB2D7P6wyQYc99


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## hotincali (May 3, 2017)

West facing Rafters


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## Bud9051 (Nov 11, 2015)

Foam board emits toxic fumes and contributes to flame spread. I'm certainly not an expert on it just a victim that has to cover it when installed. Dow went through the testing process with the Thermax to get it certified for commercial work, also applies to residential. (better advice welcome)

Getting approval to leave it exposed or using the one that is approved has the advantage of leaving the radiant surface where it can be effective. Paint it (another option with special paint) or cover it without an air gap and no radiant barrier.

But do ask your local authority as you are dealing with a garage and they may accept the one you selected.

Can't see from the pictures but is that attic space isolated from the main house with another fire barrier?

Bud


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## hotincali (May 3, 2017)

Bud9051 said:


> Can't see from the pictures but is that attic space isolated from the main house with another fire barrier?
> 
> Bud


Yes. garage is isolated from the main house.


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