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I have some sagging floor joists which I need to reinforce. I do not need to get all the sag out of the floor, but I want to get out some and stiffen it up. Joists are rough 2×8, but notched to an effective 2×5. Do I need to sister with a full size (2×6) or can I get the spring out of the floor with a 2×4. Span is just under 12′.
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How about sistering with something bigger? 2 x 8s at least. Also, I know opinion on this varies, but when I use a lot of solid blocking between it sure seems to help. Easy way out is support it from below if you can.
*I have a similar issue -- but my Q is, can he get the sag out? Jacking won't make any difference, assuming the joists took their current set long ago. I assume he doesn't know who the brainiac was who notched perfectly good 2x8's so deeply. 2x4 "sister" (more a cleat, really) won't make much difference; full size sister will actually take over some loadbearing to the sill. Partial midspan sister would stiffen some right?I removed the subfloor and shaved/sistered the joists in our house. This was not easy and is not recommended for the faint of heart. Some of the subfloor was damaged by water and long-departed termites, so it wasn't any great loss.
*I would assume Jack is limited by some piping or wiring or whatever those notches were cut for. In that situation, I've beefed up a floor joist by making exactly the joist I wanted to install (length, utility holes, etc.) and sawing through the holes to create two halves. One slipped in above the utilities and the other went under. I then epoxied and nailed them back together along that cut. Unothrodox, but it did stiffen the floor. A single 2x4 would do much (if the current "2x5"'s aren't enough). But how about a 2x4 along the top and another along the bottom? Like a TJI engineered joist with its laminated top and bottom chords and an OSB web. But in this case the existing joist would serve as the web.If there the space and headroom allows the bottom 2x4 could be nailed to the bottom of the existing 2x8 joist giving a total depth of 9 inches. For maximum stiffness and strength, you'd need to secure the bottom 2x4 to the supports at each end somehow. -David
*I believe the notches were cut to lock the joists into the ledger board, and into the beam in the center of the house. Many times this was one continuous joist from one side to the other. The notches were cut to hold the ballon framing in place. The ledger board was typically let-in to the framing.Anyways. - I take the bow out with a bottle jack. I get new boards sawn 1/4" taller than the original framing, snap lines on the walls at the ends of the joist to know where the bottom of the sister should end up. Side note - This snapped line is in all likelihood a curve at the center beam, the walls are usually still pretty straight. Then jack a little bow out, or actually get a little crown into it. Glue & screw the sister and because it's taller than the original you get a much straighter line for hanging drywall. I then add reilient furring strips for sound proofing, but the resilient leg will soak up small deviations in the rafters.I found the most dramatic improvement in floor stiffness by fastening the boards back to the original framing with screws. Blocking didn't seem to change much after the re-fastening.-Rob
*"Jacking won't make any difference, assuming the joists took their current set long ago"Andrew,Why won't jacking make any difference?Rich Beckman
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I did jack some of them up. The mastermind behind this structure cut out a joist to put in a floor furnace and neglected to double the ones to either side before he put the stove and refrigerator on top. I got them straight, but do not think the rest need to be perfect. This is just a camp on piers, not a full time residence. Some dip to the floor is "character".
*Jack, I've used this method with good results.Get your 2x6 sisters with as much crown as possible in them. Use joist hangers and /or teco,s(a-35,s work well.) Attach the ends solidly and jack the new joists down to level. Glue, nail or screw them in place. Solid blocking as described by Lonecat will add stiffness. Lots of glue when you put down the sub floor should give a solid feel.Using doug/fir joists will help also.E-mail me if you have any Q's Good Luck, RB.
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Camp on piers? How about jacking a short beam under the sag and adding two more piers?
*ditto stevei have stiffened and taken the sag out of several old floors by getting mid-span of the joists and installing a 4x4 or 6x6 across the joists. I then jack against the new timber, overjacking a little. I then put new piers under them. I have used concrete block on precast pads for piers with fairly good luck. usually i only do this on old rental type properties or a camp or something.
*Sorry, I was thinking too much of my situation. The curve in the joists wasn't because they were overloaded, but because of a curve in the foundation sill that the house settled into. Totally different.
*Jack, Here's some options:1. Build a shore wall under the joist to get them back to as level as you can. Then add a row of tight bridge blocks at about 24" on center. These bridge blocks may help to lock the floor joist in a more level condition.2. Forget trying to get the bow out of the ceiling below and just sister up the new joist to create a flat floor above.3. Build two shore walls below, cut the joist in half and hang them off a glue lam.4. Shore up the ceiling below till it's as flat as possible, then add a layer of 1 1/8" sturdy floor with construction adhesive and a shit load of screws or ring shank nails. The surface strenght of the sturdy floor may help to keep the floor joist flat.5. Forget the whole thing, put a for sale sign in the front yard and have a beer.6. Just live with the sag in the floor. ( the most cost effictive answer.)
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I have some sagging floor joists which I need to reinforce. I do not need to get all the sag out of the floor, but I want to get out some and stiffen it up. Joists are rough 2x8, but notched to an effective 2x5. Do I need to sister with a full size (2x6) or can I get the spring out of the floor with a 2x4. Span is just under 12'.