I just finished gutting out a 75 year old house. The house is 20′ wide by 50′ deep. The floor joists run with the 50′ length of the house. The joists are sagging about 1.5″ over the 20′ width. I am planning on installing hard wood flooring so I know that it is important that the floor is level. I am looking for suggestions on how to level this sagging floor at minimal cost.
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fuzzy... i think you're saying the span is about 19' 4" +/-
and how close are they together ( 16" .... 24" 32" oc )
19' span is a big span... you would probably need either a TJI or at least 2x12 sistered to the existing....
bet yours are 2x8 .... so this means you would be raising the 2d floor level... means reframing your stairs too..
nothing easy about this..
some hangers can be used to drop the bottoms below the existing ceiling level... so the floor level would remain the same.. but it's problematical either way..
anyways... you need to give more details if you want a better answer... or , you could consult a span table ...or an engineer
This may be a good place to use a beam in the cellar if you are talking about the first floor. You can build a beam out of 2x material, usually, three laminations of 2x10 will suffice. Stagger the joints and place teleposts at these intersections. The teleposts have a screw on top that, over time, you can adjust up to take most of the sag out. Don't try to do it in one shot. Place the beam at mid span.
Another method is to "sister" the existing joists. You want to do it with full length joists. It can be difficult to get the sisters in place and supported on the ends, especially with a major sag. Putting them in pieces won't help. In this case you will have to jack each joist as you go. The beam method will allow a slower approach, take less material and be easier.
Beat it to fit / Paint it to match
I have leveled a few floors and usually they have sagged because upper partititons are resting over joist that are not supported under the partitions.
Placing a beam under the floor joist is a simple solution however it is never the first choice as per needed open space.
If you are sistering the floor joist it is possible to raise large sections at one time.
However you will have to remove all wiring and plumbing crossing through the old joist. and replace after.
Use carriage bolts at one end or support the floor with a 2x4 wall If needed, Let the sistering joist hang loose at one end they will hang down the distance of your sag.
You can raise the whole floor or part as per how many adjustable floor jacks you can rent. support the sistered floor joist under with two 2x4 top plates and a 2x4 floor plate under floor jacks, and jack up slowly. When new joist are in position use carrage bolts or support with new exterior 2x4 wall using the top and bottom plates.
George
You cannot get the dip out of the joists with shoring from below. The joists have a permanent set.There are a couple of options. Remove floor joists , or sister larger joists,or add support beams underneath and fasten 2" thick framing lumber on top. Then fasten straightedge to joist and rip straight.
One other option , After installing support beams below, strip the low spots and shim. The 2" dips can be furred with 2x3's,1" dips 3/4" furring and feather in with horse feathers instead of underlayment shingles. If your flooring is 25/32" I believe 12" centers on the furring is adequate.Lightweight gypsum floor leveler may be an option? I have no experience with this with a hardwood floor covering it.
mike
I realize this is an older post but I recently had a similar problem which I corrected. So I thought I'd post my solution in case there are others who visit this discussion in the future and are looking for ideas.
I used Simpson Strong-Tie J57's to level my sagging floor. I had 13 piers which sunk away from the supporting posts. These J57's did the trick. I made a video which shows how it they work: https://youtu.be/dIP_fS0oWLo