Jacking up a floor joist

[dave11]

Am starting to jack up a 2x10 joist in my basement, that I found was split in the middle beneath a large notch put in many years ago by the HVAC installer. The joist had a non-displaced split there and had dropped about 3/4 inch. I'm guessing it had been this way as long as 50 years.

But when I went to replace the kitchen floor, I found the sag above this joist. It is right beneath the door opening between kitchen and dining room.

So my plan is to sister a 2x10, 8 feet long, across the split. The total span is 13-14 feet.

I'm using a telescoping post jack that's rated 6-10 tons, depending on the length, though they don't say what length correspond to what failure point. But how do you know when you're about exceed the strength of the jack?

 

[EatenByLimestone]

I don't think you'll have a problem. But if you want to, check the weight that a 2x10 of the length you have, can support on a span calculator. Then , if you determine that the weight is below 6 tons, jack it up SLOWLY! Like 1/4" per week. Everything else will have to readjust as you raise the floor. Expect lots of creaks and groans. Cracked plaster, pinching windows, etc.

 

[Corey]

Single 2x10? I think you'll be fine @ 6-10 tons capacity. I've lifted a few similar with a 3 ton floor jack lifting a 4x4 post to move the joist. So unless you have a dump truck parked on the floor above, it will be fine.

Curious if you're going to all the trouble, why stop 4 feet short? Why not just sister in a new, full length 13-14ft 2x10?

 

[zrock]

When jacking to want to keep the jack length as short as possible. Usually the place you rent the jack you can also get cribbing to build up a base to keep the jack closer to your work. even though the house cant move or fall over if that jack lets go or spits out someone can get severely hurt. You are also going to need something under the joist as your jacking to spread the load or the jack will just dig into the joist.

 

[shoot-straight]

When jacking to want to keep the jack length as short as possible. Usually the place you rent the jack you can also get cribbing to build up a base to keep the jack closer to your work. even though the house cant move or fall over if that jack lets go or spits out someone can get severely hurt. You are also going to need something under the joist as your jacking to spread the load or the jack will just dig into the joist.

All this makes perfect sense to me. But I am no expert.

My "builder" - I use that term lightly, missed a pier in my crawl. He put a piece of lvl vertically and had it sitting on a piece of salt treated on the footer. I jacked I up just a bit, braced then gave masonry a go. Worked out ok!

 

[zrock]

I would not call me a expert... I move modular homes and go by what I have been taught, what looks safe, and some common sense.. seen a few deaths in this business and don't want to hear anymore. It really does not take much more time to over build something and be safe. I have seen a few people jack floors using their car jack or similar and the post kick out and send them to the hospital...

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[peakbagger]

I wouldnt worry about using a screw post jack for this its the right tool. If you are paranoid about how much load you are putting into the floor you would need a hydraulic jack with a pressure gauge. Or you could buy a load cell for the post jack, but they arent cheap. With a little bit of math, the diameter of the piston and the pressure you can figure out the load pretty close with hydraulic jack. The trade off is hydraulic jacks are typically short and stubby and if you just use a post on top of the jack to reach the joist it can kick out. Its also not a good match for your project. . As a prior poster mentions, you need to do this over a long period of time, the longer the better. If you try to do it quickly things will crack creep and groan. A hydraulic cylinder will tend to leak down over a period of time, a screw jack will not.

Ideally use some solid hardwood blocking or steel at the joist and the floor to spread the load and crank the screw a small amount every day.