Making a footing for slab that already exist?

stewbstew · 03-03-2009, 05:12 PM

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

Bob Mariani · 03-03-2009, 05:36 PM

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.

jogr · 03-03-2009, 05:43 PM

Quote:

Originally Posted by stewbstew

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?

Wildie · 03-03-2009, 07:11 PM

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.

stewbstew · 03-03-2009, 08:20 PM

Quote:

Originally Posted by jogr

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!!!

stewbstew · 03-03-2009, 08:25 PM

Quote:

Originally Posted by Wildie

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!

Scuba_Dave · 03-03-2009, 08:42 PM

I doubt the Frost line is 3-4' in AZ

Wildie · 03-03-2009, 09:38 PM

Quote:

Originally Posted by stewbstew

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!

stewbstew · 03-04-2009, 03:20 AM

Quote:

Originally Posted by Wildie

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

stewbstew · 03-04-2009, 03:23 AM

Quote:

Originally Posted by Bob Mariani

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.

stewbstew · 03-04-2009, 03:25 AM

Quote:

Originally Posted by Scuba_Dave

I doubt the Frost line is 3-4' in AZ

Yeah...probably so.

Bob Mariani · 03-04-2009, 06:02 AM

call your inspector and ask.. You need to show this depth and details of rebar and such on your plans.

buletbob · 03-04-2009, 08:21 AM

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.

craneservice · 03-04-2009, 08:38 AM

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.

stewbstew · 03-04-2009, 09:54 AM

Thanks guys, that really good advice.