garage slab insulation

[jeff_gates]

I'm getting ready to pour my attached garage attached.
This slab will not have radiant heating, also it will not be a work garage.
Should we install the 2 inch f250 pink insulation under the slab?
The garage will not be heated and only be used for parking the cars.

Out side of Seattle.

Thanks,
Jeff

 

[bczygan]

I would.

Please put your location in your profile.

There are different densities from what I hear.

Bill

 

[lakeroadster]

I wouldn't... What's your location?

 

[jeff_gates]

Out side of Seattle.

 

[wssix99]

If you aren't going to heat it and aren't you going to put an insulated door on the garage, I can't imagine a reason to insulate the slab.

 

[dallasjeannie]

Depending on your future plans, I would consider the resale value. The best time to put anything under concrete is before it is poured (duh). 8 or 10 mil vapor barrier over #3 clear stone is the minimum before pouring, but adding the 2" XPS on top of the vapor barrier is a good idea that is not too expensive. But then only one step further, if you install 1/2" id barrier pex lines spaced 8" or 12" for radiant floor heat your floor will be ready for radiant heat should someone in the future decide to finish the job with a water heater of sorts. You can skip the heat source and controls yourself since that can be the expensive portion, but the resale consideration is a plus. Depending on the location and value of your property this plus could add 5-10% to the listing price.

 

[Majordisorder]

If not heated and not a work area, you will benefit most from a good vapor barrier.

 

[lakeroadster]

If not heated and not a work area, you will benefit most from a good vapor barrier.

Define "Benefit"...

The American Concrete Institute’s (ACI) Committee 302 “Guide for Concrete Floor and Slab Construction” suggests that a vapor barrier may not be necessary where no drainage or soil problems exist and in arid regions where irrigation and heavy sprinkling are not done.

Strength.
Concrete placed over a sand bed was more than 30% stronger than concrete cast on the polyethylene.

ACI 302 indicates that placing concrete in direct contact with a vapor barrier increases slab curling.

Read the details here: http://www.stegoindustries.com/docs/Vapor Barriers Under Concrete Slabs.pdf

http://www.garagejournal.com/forum/showthread.php?t=326215

 

[Jess]

As already suggested, I'd go with a decent 10mil poly vapour barrier, at least 2" of XPS foam, pex pipe for future heating, rebar reinforcing and a decent concrete mix. Once the floor is poured, you can't go back and do any of this stuff. Lots of opinions and many are based on location and experience. Ask a decent concrete contractor that does work in your area.

 

[matt_i]

Personally, unless you are laser focused on radiant heat, or want it in the future as more funds become available, I think the XPS under the slab is a waste of money.

I would do rebar or welded wire mats. I would do a vapor barrier. I would do washed, crushed limestone same depth as concrete. I would compact the subgrade if disturbed. I would compact the limestone. I would use chairs or dobies and not hook the mesh up into place.