# should Garage Slab connected to Footing?



## Bondo (Dec 8, 2007)

Ayuh,.... 'round here a garage slab is poured as a floatin' slab, with thicken edges,...

In essence, the slab, 'n footer is a single pour,...


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## stadry (Jun 20, 2009)

down here turn'd down edge (integral mass) OR std footing + floating slab on top,,, my garage is attached but the latter


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## JohnnyC (Nov 14, 2015)

Thanks for your replies so far. 
I am a DIY homeowner and I think the design I have is a bit excessive in some details and this is one of them. 

I'd rather not do this because:

1. Haven't seen anyone else do it and why spend the extra $30 bucks and effort on this rebar; but more importantly

2. Around here the footing is poured first, then the garage is built, then the floor slab is poured later - having that rebar sticking up from the footing and waiting for the slab is a big safety hazard; and

3. Seems to me the floating slab should float...and be allowed to shrink and expand with the seasons...pinning it to the footing would only invite cracking ?
:vs_worry:


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## MTN REMODEL LLC (Sep 11, 2010)

Even in cold country of Colorado... the stem wall off the footer and slab are not tied... of course our footer and stem are alot deeper.

HOWEVER, the structoral on my son's in warm SoCal called out the footer (18" dEEp) barred into the SOG.???

I would like to know the structural considerations and logic....

Sorry.... Not a very good answer...


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## Fix'n it (Mar 12, 2012)

JohnnyC said:


> 2. Around here the footing is poured first, then the garage is built, then the floor slab is poured later -


my mother-in-laws garage was built like that. that garage is a pile of junk. 
the foundation settled in all different directions, as did the separate slab.
bad bad bad.


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## Daniel Holzman (Mar 10, 2009)

The footer is a structural element that holds up the framing. The slab has no structural function, it is simply there to provide a hard walking surface. The goal of the footers is to make sure the building remains plumb and level, i.e. no settling, so the the footer needs to be large enough and deep enough to resist settlement under load, and typically has some rebar in it to provide tension strength in the concrete.

The slab can be poured with no rebar at all, which is typical. There is no reason to tie the slab in to the footers. This is not because the slab wants to move around with the seasons, concrete has a very low thermal coefficient of expansion, and should not "move" with the seasons. The slab should remain in place due to friction without need to connect to the slab, and since the slab is so thin (4 inches), it is not possible to place structural reinforcing in the slab.

Of course you want your slab to remain level and not settle, and that requires adequate preparation of the base material. You need to excavate down to natural mineral soil, backfill to appropriate grade using structural fill, compact the fill, then place your slab. Local building codes will typically dictate minimum excavation depth, minimum depth of fill, and the makeup of the structural fill. In earthquake zones, design of the footer and slab may be different, since the slab can be subject to severe tension loading during an earthquake, hence you may need steel reinforcing and probably a thicker slab than in standard practice. Or you may accept that the slab will be damaged in an earthquake, and plan to replace it. Best to talk to your building inspector, I am not sure what earthquake zone Vancouver is in.


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## MTN REMODEL LLC (Sep 11, 2010)

Dan.... As usual, thank you for the clear clarrification and understanding.

Your earthquake country qualification very adequetly explains my son's structural call out here in SoCal... and although we did two pours barred together... an alternative would have been a mono-pour of footer-slab together.

Thanks and best


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## JohnnyC (Nov 14, 2015)

Dan... thank you for your comprehensive reply. Makes perfect sense.

On the West Coast here, seismic concerns seem near the top of the list for major building construction - but I think the concerns gets carried too far sometimes - especially for the likes of my residential garage.

I often see places adding all that rebar in the floor ...I wonder if it's because that once cracks develop, and of course they happen even early on, owners tend to get a bit upset. The first thing friends and family say when they gaze at the crack is "is there rebar in there?" So the contractors have learned to throw the rebar in there, at the owners cost, to protect themselves from criticism later on... just an opinion.

Now I also need to also query the Engineer on that rebar in the floor. http://www.diychatroom.com/images/smilies/glasses.png


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