# Slab on Grade



## Polaris900 (Jan 28, 2010)

Hello,

I have a job that the owner wants a slab on grade for a two story garage that he wants attached to his house. Will a slab on grade be ok. Because the frost depth is about 4 feet. I am worried it might heave and detach from the house which is 40 years old.

Thanks
Steve


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## jlhaslip (Dec 31, 2009)

Handle the addition the same way as the house. Footings as per the building you are attaching it to.

For Northern, cold climates, you need to be at least below frost.

You don't list where you are from, so please edit your profile to state your area, if not your city.


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## CONCRETE MIKE (Jan 11, 2010)

jlhaslip said:


> Handle the addition the same way as the house. Footings as per the building you are attaching it to.
> 
> For Northern, cold climates, you need to be at least below frost.
> 
> You don't list where you are from, so please edit your profile to state your area, if not your city.


 :clap:


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## CONCRETE MIKE (Jan 11, 2010)

You need concrete or block footers, no floating slab.


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## bytor (Jan 23, 2010)

In our area, code requires that anything attached to a dwelling have a full foundation to below the frost line (5 ft. depth for us) Could only get away with a floating slab for a fully detached structure


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## Polaris900 (Jan 28, 2010)

Thats what I was thinking putting down to the original footing, so there won't be any issues.

Thanks


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## jomama (Oct 25, 2008)

I definately agree with those above, footing to match existing or deeper.

BUT, we actually did a small project a few years ago where we did the foundation for a breeze-way connecting a house with full foundation to a floating slab garage. It's the only time I've seen it done permitted, as well as the carpenter/GC and building inspector. Everything needed expansion joint between the 2 structures, from footing to walls to siding to brick wainscoat. The roof was the most complicated element as I understand, as the breezeway roof literally rested on the garage - no actual fastening. It also required some real strange valley flashing procedure accordign to the carpenter.

All said & done, I'm sure it cost more than just tearing the garage down & starting over with full frost walls. I'm fairly sure the only reason they didn't go this route is that the garage was encroaching on newer set-back limitations.


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## scrapecc (May 11, 2009)

Some places you can use a thickened edge slab with piers. But you have to check with your local code authority.


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## JD3lta (Nov 22, 2009)

It's got to be thick enough to hold serious weight unless they want a ramp, might as well bury it. Regardless there's probably a code unless it's on private property out of view somewhere far from the main road.


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## concretemasonry (Dec 1, 2006)

The bottom of the footings should be at least as deep and the house footings and below frost.

Use stem walls high enough to get the sill 6" to 8" above the finished floor. Pour a true flat floating slab on compacted soil between the stem walls at the desired grade. This will allow you to easily slope the slab to a central drain or any direction you wish. This also gets your wood the required 6" above outside finished grade. It also is much easier to clean out or wash the garage floor.


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## CONCRETE MIKE (Jan 11, 2010)

concretemasonry said:


> The bottom of the footings should be at least as deep and the house footings and below frost.
> 
> Use stem walls high enough to get the sill 6" to 8" above the finished floor. Pour a true flat floating slab on compacted soil between the stem walls at the desired grade. This will allow you to easily slope the slab to a central drain or any direction you wish. This also gets your wood the required 6" above outside finished grade. It also is much easier to clean out or wash the garage floor.


 :clap:


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