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Old 03-03-2009, 04:12 PM   #1
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Making a footing for slab that already exist?


After going to the county to get a building permit, I find out that I will need to make footing for a slab that already exist. Does anyone have any suggestions?

Thanks!
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Old 03-03-2009, 04:36 PM   #2
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Making a footing for slab that already exist?


The footing needs to be at the frost line. Did the building dept tell you what this is? Can you make the footing and new foundation wall along side this slab? then use a expansion joint between the slab and the foundation wall.

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Old 03-03-2009, 04:43 PM   #3
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Making a footing for slab that already exist?


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Originally Posted by stewbstew View Post
After going to the county to get a building permit, I find out that I will need to make footing for a slab that already exist. Does anyone have any suggestions?

Thanks!
stewbstew
What kind of slab are we talking about? A patio? A house? Is the footing to support the slab or some structure on the slab?
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Old 03-03-2009, 06:11 PM   #4
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Making a footing for slab that already exist?


I had to do this recently! The frost line in my area is greater than 3 feet. I had to dig down to the 4 foot level and pour a pad, 16" square.
Then I notched out a Sono tube, so that half of it fitted under the under-side of the slab!
I then back-filled the tube to keep it in place!
Then I filled the tube with cement!
It would depend on what you plan to erect, on how many of these piers would be required.
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Old 03-03-2009, 07:20 PM   #5
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Making a footing for slab that already exist?


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Originally Posted by jogr View Post
What kind of slab are we talking about? A patio? A house? Is the footing to support the slab or some structure on the slab?
Yeah, its a patio type of slab that was turned into a laundryroom, however, I don't think they got a permit to do so because it was a mess. Actually, I was trying to remodle it to breing it up to code.
Anyway, so I live in Arizona, and I not sure if the frost line is a factor. Therefore, do you think digging down the side of the slab and in about a foot then pour concrete into area I dugout?

Anyway, thanks so much for replying!!!

Last edited by stewbstew; 03-03-2009 at 07:22 PM.
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Old 03-03-2009, 07:25 PM   #6
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Making a footing for slab that already exist?


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Originally Posted by Wildie View Post
I had to do this recently! The frost line in my area is greater than 3 feet. I had to dig down to the 4 foot level and pour a pad, 16" square.
Then I notched out a Sono tube, so that half of it fitted under the under-side of the slab!
I then back-filled the tube to keep it in place!
Then I filled the tube with cement!
It would depend on what you plan to erect, on how many of these piers would be required.
Thanks for replying!
So...do you think digging down the side of the slab about 3 or 4 foot and in about a foot then pour concrete into area I dugout will work? Thanks again!
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Old 03-03-2009, 07:42 PM   #7
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Making a footing for slab that already exist?


I doubt the Frost line is 3-4' in AZ
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Old 03-03-2009, 08:38 PM   #8
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Making a footing for slab that already exist?


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Thanks for replying!
So...do you think digging down the side of the slab about 3 or 4 foot and in about a foot then pour concrete into area I dugout will work? Thanks again!
I'm in Canada, so the temps stay below freezing, months on end!
I'm unsure what your frost level would be, but I doubt that it would even be 12".
In my case, the building inspection people advised me on how deep to dig! Can you not find out from your inspection dept. what is required!
In your case, I would dig a trench around the perimeter. Perhaps 12" deeper than the bottom of the pad, then undermine it for about 8". Then fill the trench with concrete with rebar running parallel and under-neath the slab a few inches!
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Old 03-04-2009, 02:20 AM   #9
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Making a footing for slab that already exist?


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Originally Posted by Wildie View Post
I'm in Canada, so the temps stay below freezing, months on end!
I'm unsure what your frost level would be, but I doubt that it would even be 12".
In my case, the building inspection people advised me on how deep to dig! Can you not find out from your inspection dept. what is required!
In your case, I would dig a trench around the perimeter. Perhaps 12" deeper than the bottom of the pad, then undermine it for about 8". Then fill the trench with concrete with rebar running parallel and under-neath the slab a few inches!
Okay my friend, we'll look at that. Thanks
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Old 03-04-2009, 02:23 AM   #10
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Making a footing for slab that already exist?


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Originally Posted by Bob Mariani View Post
The footing needs to be at the frost line. Did the building dept tell you what this is? Can you make the footing and new foundation wall along side this slab? then use a expansion joint between the slab and the foundation wall.
Hi,
no they did not tell me what it was, he just told me to come back with plans on the foundation and I guess he'll tell me yes or no then. Go figure. Anyway, thanks for the suggestion.
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Old 03-04-2009, 02:25 AM   #11
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Making a footing for slab that already exist?


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I doubt the Frost line is 3-4' in AZ
Yeah...probably so.
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Old 03-04-2009, 05:02 AM   #12
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Making a footing for slab that already exist?


call your inspector and ask.. You need to show this depth and details of rebar and such on your plans.
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Old 03-04-2009, 07:21 AM   #13
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Making a footing for slab that already exist?


Yes call your building dept. and find out what your footing depth should be. And wildie has the right approach, that's called underpinning. BOB. Is the slab at least 6"- 8" above grade. Be cause if its wood framed this might be a problem with the sill plates not meeting the code height. BOB.
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Old 03-04-2009, 07:38 AM   #14
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Making a footing for slab that already exist?


You may have to pour the footer and stem wall in sections in order to keep the slab supported. You must leave at least an inch of space between the stem wall and the slab. Fill the gap with non-shrink grout if you pour to the bottom of the slab with concrete when the concrete sets it will pull away from the slab and leave a small gap. The slab will then be unsupported until it settles or cracks to sit on the stem wall.
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Old 03-04-2009, 08:54 AM   #15
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Making a footing for slab that already exist?


Thanks guys, that really good advice.

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