Anyone previously leveled deflecting joists?
I am working on a 1960’s platform framed house that is generally very well built but there is one room where the natural 3x10x16′ @16 joists have deflected 3/4″ at the center, and I want to level the floor above. The joists have X bridging in the center and have 8″ resting on the i beams at either end. The subfloor is 4″ planks set at 90 degrees.
I cannot take up the subfloor above, and there is a tiled bathroom above as well, probably at least 15 years after the house was built (the style makes me think the bathroom is from the late 1970’s). The bathroom will likely be removed in about 12 months and so cracking can be lived with, but the basement is being finished now and the room above will eventually get new floors (just not this year).
I’m bringing in 2 8″x12′ steel beams anyway, so I am considering how to fix the floor and though I might make use of them. What I am thinking is to place one underneath across the middle of the joists, setting jacks on steel plates to not crack the slab, and jacking them over several weeks until the joists are level. I’d then put in whatever my engineer calls for and sister the original joists, but I’ll assume the originals are not capable of carrying any load without deflecting again, since they have already been deformed, so I’ll design the new lumber for the full load.
So, my question:
My biggest concern, other then eventually repairing the tile and plaster upstairs which will likely crack, is that the joist ends will rise off the I beams they rest upon instead of the joist returning to level, though I plan to do the operation over several weeks, 1/8″ each day. The end rising does not seem likely on one end of the joist, since there is a load bearing wall above, but on the other end it is only carrying a partial floor load.
Has anyone repaired deflecting joists this way (or any other way) before, and how did it work?
Any issues you are aware of I amy not be considering?
Thanks!
Replies
or any other way
My favorite method (successful 4 out of 4 times), even with just a 2x joist, will work very well with a 3x joist.
For 3x joist, get steel strapping 2-1/2" or 3" wide, by 0.1" or 1/8" thick. Using drill press, predrill 3/8" holes at spacings your engineer (since you referenced such) specifies for resisting lateral shear - e.g. more 3/8" bolts at the ends and very few near the center. Do NOT oversize the holes, a tight fit on the bolt is desired.
No need for the strap to be on the end bearing of the joist, can be a few inches shy. Jack each joist individually at the center till about 1/8" bowed upwards, install all bolts.
Remove th jack, joist should be level, move on to the next joist. You can adjust the upwards bow + or - depending on how close to dead flat the first joist ended up.
Have done this on 2x10s, 2x8s, 3x12s, and even on a 16 foot 6x12 (used 5" plate) over a garage door.
Other folks have glued/srewed 2x4 to the bottom edge in similar manner, but you need to leave the jack in place until the glue develops near rated strength.
PS: 1st one was on brother's house with 1"+ sag on 2x8s on 14 ft centers! 30 years later the floor is still dead flat. One intermediate wall with lath and plaster (1920s house) that was non-bearing showed some cracks that needed to be fixed after jacking, should not have that on a load bearing wall with load above.
leveling joists
This sounds like a good approach, and 4 for 4 recommends it. I'm still concerned about the ends lifting when I jack it, and one of the other replies suggested cuting the joist, then sistering and jacking.
Did you ever have issues with the wood not wanting to go level?
Thanks
issues with the wood not wanting to go level
It takes about 2 tons to deflect a 3x10 3/4 inch.
So, a 3T jack in the center against the steel plate will put about 2000# on each wall at the joist ends.
If the wall is a shear wall (for the age, diagonal wood?) you are in good shape, the upward force on single joist will be attempting to lift the entire wall. Assuming a 10 ft by 8 ft load above, and a 15#sf dead load pls weight of the wall, there is likely over 2000# load on the joist end downwards, so you are good.
However, if the wall above is lath and plaster, you better watch for cracking as you jack, as the single joist will 'try' to raise just that section of the wall, and there is not much elasticity in old plaster.
Found in one case (jacking each joist over the course of a day, not all at once) that 4-5 100# bags of sand stacked on the floor above the ends of each joist being jacked alleviated the cracking.
Not a 'quick fix', after all, the 3x10s have had decades to sag.
If my own house, I'd fix plaster crack before I'd ever cut an existing joist (unless there is rot or already broken)
another thought..
From your description of the joists it sounds like it might be rough cut lumber?
If so they might have been installed green [high moisture content]. If that was the case the joists could have developed the sag as they dried in place. That might make them really hard to straighten up.
A 3/4" crown down over a 16' span isn't the end of the world.
leveling joists
I don't think they were green - none of the other joists in the house have the problem, and I just gutted another of his houses 4000 s.f. from the same street and year, and all the lumber (also 3x10, identical looking stock) was in fine shape and level. There is also no twisting which I'd expect if it was drying on site.
I think what has happend is this was an unusual design for him (modified cape with a shed entry) instead of his usual colonial) and he has a point load that was not properly accounted for.
Not everything in old houses can be fixed and 3/4" isn't huge, but in this case it is an expensive house and the problems it caused are noticable even if you barely look - some doors don't hang right with 1/2" gap at one jamb, and the floors clearly slope and creak extremely badly. Since the floor upstairs will get replaced eventually and I can fix the subfloor then, I want to try to make the joists right now while it is open below.
Sister on from above when you fix the flooring
I'd recommend waiting until you do the flooring repair above. Since you are planning to replace the subfloor anyway, I would wait until the subfloor is off, and then sister on with 2Xs to the existing joists.
I don't think you're going to get that much deflection out of a 50 year old 3 X 10 in just a couple of weeks, if ever. I've done sagging roofs much worse than that by cutting the old rafter in two, sistering a new 2X beside the old one, jacking them both up and nailing them together.
leveling joists
interesting ... I thought of making a kerf cut on the joists bottom but was concerned about the structural ramifications - cutting it in half would be pretty serious!
When you have done this on the roof you have a much smaller load, especially if it is a gable, but do you support the middle you are cutting so it does not fall away, and how? I guess to be prudent I could reinforce the flanking joists in their middle with a post/wall temporarily.
I would gradually jack up the joists (over days) until resistance is met. I'm sure some sag could be taken out. Then use junkhounds method of reinforcement.
How does the strapping approach work for bounciness of the floors? I'm getting closer to a crawlspace extravaganza to finally reinforce my living room floor and that's more my goal than fixing the deflection. I have 2x10s on 16" centers with a ~13' span. I was planning on putting in a built up beam at midspan supported off 2 new footers/piers.
I've already been in there to fix a joist in the same room that has a punky end. I jacked and sistered in a new section at the end of the joist. The joists are notched and rest on a 2x4 attached to the double 2x10 main beam. When I did this, it helped with an uneven floor transition above (where we opened up a new doorway between rooms during a remodel). I'm thinking about jacking the joists again and maybe shimming them off the 2x4 to correct the uneven spot. The alternative, I think, are the Simpson structural angles and their screws.
just curious what method you went with and how it worked out. any method work the best?