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Old 07-03-2012, 11:35 AM   #1
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slab under carport sinking


The concrete slab beneath my carport is, albeit very slowly, sinking. It has a big crack down the middle lengthwise and also at each corner. I can tell the roofline begins to sag downwards over the carport. I want to correct this problem myself (or as much myself as possible/realistic) so I thought I'd solicit some thoughts/advice. Itís a 1-car carport attached to the house. My carport shares the roofline with the rest of the house and is supported by 4x4 posts.

So, the obvious problem is the original slab was poured 50 years ago before the carport was built and now I have to figure out how to replace the slab with the carport in place. I would guess I can build some kind of temporary supports while I have the old pad removed and repoured and then use jack posts to level the carport structure and then replace the posts. The question would be how exactly to go about that. I was thinking maybe it would be a good idea to have footings within the new slab underneath where the posts are instead of just the slab. I mean the minimum code for a deck footing here is 24" so I don't see why I would want my carport structure just sitting on a 4 or 5 inch concrete pad.

Anyway, right now Iím only at the point of thinking about this, so Iím open to any suggestions or other ideas. Thanks!

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Old 07-03-2012, 12:44 PM   #2
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slab under carport sinking


Without a picture it's hard to say.
But your right there needs to be footing where the post will be.

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Old 07-03-2012, 12:57 PM   #3
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slab under carport sinking


Yep--You might want to build a jack wall to lift the structure back into position--then remove posts---add proper footings (sono tube piers) then replace the posts--

after that you can take care of the slab--
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Old 07-03-2012, 01:00 PM   #4
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slab under carport sinking


We had this happen with our garage that had been built on a slab. We managed to pour 42" deep footings while saving the garage (and bring up to code), cost $4000 since we contracted it out. We had them raise the footings a few inches to match the height of the driveway (for future repaving). If it can work for a garage, it can certainly work for a carport.

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Old 07-03-2012, 01:18 PM   #5
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slab under carport sinking


Thanks for the replies. So, if I want to correct the posts/structure first I could support the structure (oh'mike, what exactly is a jackwall?) and then jackhammer/dig down however many inches I need to for the piers (will check code, assume it's probably 24" or more since that was the code for my deck here in northern VA) and reinstall the posts...then next remove the old pad and repour...would there be any issues creating a cold joint at the pad getting poured around the piers?

I'll try to post pictures later on so you can see what I'm working with.
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Old 07-03-2012, 01:38 PM   #6
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slab under carport sinking


Have you ever built a regular stud wall?

A jack wall is similar --except you intentionally cut the studs to long and pound them into place with a big friendly hammer(BFH)

Attach a plate to the bottom of the roof support

Lay one on the ground directly below

Measure for a stud--ad 1/4 inch or less( 1/8" is ideal if the lift is heavy)

Toe nail the top

Use the BFH to pound the stud(s) into place--

Cut longer studs and repeat as often as needed--doubling up the bottom plate is also an option if the lift is great and you don't want to keep wasting studs.

I've lifted a garage front 4" using jack walls.
And entire houses to replace rotted sill plates.
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Old 07-03-2012, 03:11 PM   #7
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slab under carport sinking


Thanks Mike, I have built an ordinary stud wall before but never a jack wall but sounds like it would work. How does it compare to using the metal jack posts that screw at the top? Easier, harder, cheaper?
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Old 07-03-2012, 03:20 PM   #8
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Much easier and safer---save the jacks for lifting up a truck--
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Old 07-03-2012, 03:31 PM   #9
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slab under carport sinking


I've used these a lot over the years---

Jacks are dangerous---when used with wood--to much point load in one place---wood can crush,split and then the jack goes flying--

Try it--you will become a believer.

I pulled up close to 3 inches if sag in a house with improperly built trusses---roof ridge looked like a sway backed horse--

I uses 2x6s on that one--very heavy lift--lift time--about one hour--

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