replacing sagging floor joists- Advice anyone?

17 years ago

I have a fairly large farm house in which every room, on the first floor, suffers from sagging floors. The span for each room varies from 12' to 16'. Regardless of span, all floors have 2x8 joists-true 2x8 joists and made out of oak and chestnut but obviously insufficient. I've thought about lvls, flitch beams, and have actually put steel I-beams with jack posts under a couple already (as a temporary fix until I find a permanent solution). One of the problems with the already too small joists is that each one is mortised into an oak beam. So, at the ends, the joists are actually 2x3. These joists are over 100 yrs. old and deflection is so bad I'm thinking about getting them out of there. My idea is to replace them with new 2x12s or 2x10s (depending on the room) which will be tied into another 2x12 which I bolt into the original oak beam (like a ledger board). I figure this will allow me to level the floors as well. Since the beams are 6x8 I plan to screw a joist shelf onto the bottom of the ledger boards and then use joist hangers to tie in the new joists to the ledger. My 3 and 5 year old kids love the spring action in the floors but I'm sick of my desk drawers coming open on their own. Is this solution a solution?

Comments (9)

bus_driver
17 years ago
If this is over a crawl space, adding piers to stiffen the floor system should be fairly easy. Given my shop facilities, I probably would jack to the desired height near where the permanent post is to be, place a precast concrete pad leveled in sand at the post position, measure and make a fixed-length steel post for that location. I think those pads on dry soil will provide completely adequate support.
angusmc
Original Author
17 years ago
These floors are 6 1/2' above a post-poured basement. Anything I put under the joists to jack up the sag sacrifices any head room in the basement. I already have a dozen jack posts in the basement under the beams in various locations.
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ron6519
17 years ago
Since these joists are going to have "memories" of this sagging shape, I think it will be hard to jack it up into position. Since you want to maintain headroom in the basement I would put a main beam in the middle of the floor engineered for the span. Maybe two LVL's around a 1/2" steel flitch plate, bolted together. You would cut out a gap down the middle of all the floor joists. Insert the LVL sandwich and jack it into the height you want. Attach the individual joists to the LVL sandwich. This will require temporary support walls, jacking into position both sides of the bisected joists and a few other issues. If there's a second floor involved, it's more complicated due to the extra loads involved. Depending on the depth of sag, expect to patch walls and possible rehang doors.
The size of the beam would need to be spec'ed out by someone who knows what they're doing. This is not a "best guess" project.
Ron
hendricus
17 years ago
In our last home I had the same problem on a second floor bedroom. Removed the floor and sistered 2x6's to each joist and placed a new subfloor and floor. I could not remove or straighten the existing joists be cause the downstairs ceiling was plastered and looked level. It was very sturdy when I was done. My son had a waterbed in there for many years.
angusmc
Original Author
17 years ago
ron and hendricus,
ron-I don't have to worry about doors or walls. The beams that are under each wall have already been jacked level and the walls were reframed, repaired and drywalled. They won't move when I take out the floor. Some of the rooms are near 17' across so, the deflection is pretty exterme in the old joists. I'm pretty much settled on using them for furniture (or firewood) in the next few years. The subfloor is 3/4 tng pine plank, ie garbage. The flitch beam sounds like a good idea but I do want to rid myself of the old joists.
hendricus,
How far of a span did you have for your sistering efforts? I've thought about sistering but the mortised joints move so much I'm worried that the desired result would fall short.
So guys -is my original idea overkill?
hendricus
17 years ago
12' span of 2x8 and used 10' 2x6. Couldn't go all the way to the ends. If you can remove the old joists and replace with the proper size that is the way to go.
Hank
brickeyee
17 years ago
Inst4ead of bothering to remove the old joist, use a flitch plate and sister a new joist.
You can download Superbeam for 30 days for free if you want to see what various rgades and sizes of joists will do at your span, and it does flitch beams.
The portion missing for flitch beams is the fastener schedule through the wood and steel.
You use enough and correctly sized fasteners to not exceeed about 50% of the cruch resistance of the wood members.
A flitch between I-joists will not be as efeective since the buckling support is reduced, and 1/2 inch plate is probably overkill.
brickeyee
17 years ago
The only hard part about Superbeam is the loading.
Main floors are 40 PSF live, 10 PSF dead for a total of 50 PSF.
Superbeam accounts for live and dead.
If the joist are on 16 inch centers the load per foot of joist (the number superbeam needs) is 40 PSF L * 16/12 = 53.3 pounds per foot L and 10 PSF D * 16/12 = 13.3 pounds per foot D.
Watch out for the wood grades.
ron6519
17 years ago
The plan you propose would straighten the floor and reduce the bounce. You could also install a series of blocking to further reduce the bounce and sort of unitize the floor. You could further reduce the deflection by putting the joists 12" on center. I did that on a kitchen addition, using 2x10's with a 14 ft span. Solid blocking every 4' or so. No bounce at all. Ends up using 2, maybe 3 more joists.
You could sell the old joists for a pretty profit if you can get them out in decent shape. 100 year old chestnut and oak could pay for the new materials easily. You probably have a few grand in those beams.
Ron