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Adding footings to an existing slab

Posted on 3/5/23 at 7:32 pm
Posted by Success
Member since Sep 2015
1730 posts
Posted on 3/5/23 at 7:32 pm
Can footers be added to an existing 6” slab? I need the footers per permitting to building my metal shop. I haven’t called anyone yet. Just seeing what the TD experts can tell me.
Posted by Civildawg
Member since May 2012
8611 posts
Posted on 3/5/23 at 8:12 pm to
I don’t understand the question really. I’m assuming it’s a slab on grade. Why would you need a footing on an existing foundation? Are you needing spread footers for building columns?
Posted by Adam4848
LA
Member since Apr 2006
19044 posts
Posted on 3/5/23 at 8:48 pm to
You could certainly dowel in a pedestal on top of a 6in slab for light columns etc…depending on what kind of loads you have it’s difficult to assume that they 6in slab would actually take the load.
Posted by Success
Member since Sep 2015
1730 posts
Posted on 3/5/23 at 9:55 pm to
It’s a metal building. Not much to it. Permit requires 12” footing on the slab. I don’t have them. Or can I just file a variance? I’m a typically homeowner who doesn’t know anything about this.
Posted by JAMAC2001
Member since Jan 2013
2764 posts
Posted on 3/5/23 at 11:28 pm to
Is it a red iron style or the carolina carport style.

I did carolina carport and ran into something similar. I had to get the drawings from carolina carport showing that footings arent required to support their buildings the way the load is distributed.

The red iron style i believe need footings.
Posted by Success
Member since Sep 2015
1730 posts
Posted on 3/5/23 at 11:39 pm to
Carolina carport style
Posted by TDHELPCENTER
Member since Nov 2022
226 posts
Posted on 3/6/23 at 8:35 am to
Not sure about the code and what not but look into drilling piers underneath existing slab.
Posted by LSUDad
Still on the move
Member since May 2004
58949 posts
Posted on 3/6/23 at 9:31 am to
This one is tricky, could a cable lock help? Do you need a permit? Too many questions.
Posted by SurfOrYak
BR/MsDelta
Member since Jul 2015
406 posts
Posted on 3/6/23 at 10:27 am to
The 6" concrete slab is a thick driveway, not enough for footings to support weight-bearing posts. I would want the 12" deep footings under all the posts, so yes, cut out the concrete slab in those areas and put in footings. You still need to know the other dimensions of the footing to cut out enough of the slab.
Posted by junkfunky
Member since Jan 2011
33995 posts
Posted on 3/6/23 at 11:37 am to
That requirement doesn't necessarily have to do with supporting the building. Up north the purpose is to get deep enough for the freeze/thaw line and down here it is about preventing washout. Is the slab on an elevated pad?

Eta
Is the building installed yet?
This post was edited on 3/6/23 at 11:38 am
Posted by cgrand
HAMMOND
Member since Oct 2009
39049 posts
Posted on 3/6/23 at 11:47 am to
quote:

That requirement doesn't necessarily have to do with supporting the building.
its not about supporting the building, its about uplift
Posted by junkfunky
Member since Jan 2011
33995 posts
Posted on 3/6/23 at 2:37 pm to
A 12" square shovel beam around the perimeter only weighs about 100 pounds per linear foot. You need more meat than that if you're trying to resist uplift. We sometimes use them to support light loads but completely ignore that weight when considering uplift.

Speaking of metal buildings, did you hear about that collapse on Burbank?

eta: Just remembered he said a 6" slab so the beam would be more like 85 plf.
This post was edited on 3/6/23 at 2:44 pm
Posted by cgrand
HAMMOND
Member since Oct 2009
39049 posts
Posted on 3/6/23 at 2:55 pm to
quote:

A 12" square shovel beam around the perimeter
24x24 is standard
Posted by junkfunky
Member since Jan 2011
33995 posts
Posted on 3/6/23 at 3:20 pm to
quote:

24x24 is standard
I assumed we weren't talking about grade beans since the slab is already in place. You can undermine and install a shovel without demoing the existing. I'm really curious about the other poster who got a letter from Carolina stating a mat is sufficient.
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