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Add pillars to joists that span 12 feet in 80 year old house


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I live in a 1940's house that has sunk and settled a lot over the years. The joists span 12 feet from sill to sill with no support in the middle. In one place there is a bathroom, pantry, and staircase that sits on these joists. The floors have sank about 1 1/2 over the 80 years it's been there.  There is a lot of duct work, plumbing, ect... So running a 4*6 in this spot is near impossible. My question is what kind of piers/ pillars could I add under each joist to stop it from sinking more?

Thanks in advance

Brandon

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For simple 40psf floor loads, the 2x10s ought to be able to span 12' without any problem. It sounds like you've got a point load or a bearing wall somewhere that's overloading the structure. If you can't get a girder in there, directly under the load, then you could use small concrete piers and posts under each joist. Just be sure to excavate down to firm undisturbed soil before placing the concrete. Then jack up the joist a smidge before placing the post. It's a tedious job and will necessarily be sloppy, but it should stabilize the floor.

Personally, I'd remove the obstructions and install a proper girder. 

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Above this spot there is a bathroom, staircase and pantry. Nothing but joists holding it all up and the walls are solid wood with wood bead board so it's very heavy. Jim Katen would I measure the wood posts and cut them a little longer than the distance needed? To account for where I jack it up?

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6 hours ago, Brandon Downer said:

Above this spot there is a bathroom, staircase and pantry. Nothing but joists holding it all up and the walls are solid wood with wood bead board so it's very heavy. Jim Katen would I measure the wood posts and cut them a little longer than the distance needed? To account for where I jack it up?

If there's a staircase, isn't there also a 2nd floor above this area too? You should find out whether or not the 2nd-floor joists bear on a 1st-floor wall and put the additional supports below this wall. 

Doing a job like this takes experience. Otherwise, you'll just go from a sagging floor to a lumpy floor. I strongly suggest hiring someone who has that experience. Maybe that person will work with you to keep costs down. 

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3 hours ago, Brandon Downer said:

Would I pour concrete then put the concrete Pier on that or put the pier directly on the dirt?

It depends on your dirt. With some firm, stable soils, you could get away with a portable pre-cast pier pad - especially if each one will only be holding up one joist. 

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If you are on expansive soils, it is important that any pier, post, or pad used to support the foundation joists are placed similarly to the other foundation. Just dropping a pad and post on top of the soil when the rest of the house is supported by a much deeper foundation can have the foundation "fighting" with the newly added item. Shallow or surface soils move much more relative to the deeper foundation and the "fix" becomes the problem rather than a solution.

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Call one of the many "foundation repair companies" we have here in SC. I'm not sure whether I can give out company names on this forum so PM me if you'd like and I can give you a few of the names.  

These large "foundation repair companies" are capable of properly repairing your issue if it is indeed unsupported load points overloading the structure and not a foundation issue.

Jim is correct that finding an experienced contractor is tough and the usual result from an inexperienced contractor is a floor with even more dips/sags and humps.

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...a carpenter friend bought a hundred + year old home 40 yrs ago.  Pine floor frame had sagged away from a central, double flue, rock and brick chimney column.  He tried to straighten things with big jacks, but when he lifted, everything lifted together, so he ended up re-framing floors in pieces.  With a lot of patience he finally got it right and still lives in a beautiful home.  Warning: this kind of project will never be featured on "Flip this house" programs.

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