Warped Joists! Should I sister or block them?
2/7/2021 at 5:59:58 PM
My house has been built in the 80's and I've found the floors relatively bouncy. I've been taking a long hard look the main floor joists in my basement and taking a speed square, found almost all of the joists twisted in one form or another. I've attached some photos to look at how they're twisting. I was planning to add blocking in between these joists but after finding how warped these joists are, now I'm not so certain. And looking at how some of these joists meet up with the rim joist, they appear to be twisted all the way to the end. Will blocking help straighten out these joists?
The existing cross bracing doesn't appear to help as they don't look that secure and may have loosened over the years...as well as some that look like they were installed lazily. On this note, would it make sense to replace the cross bracing instead? I've seen a lot of videos of installing cross bracing but they all seemed to add the cross bracing from the top, before the subfloor is added and during actual house construction. Can cross bracing be replaced from underneath the floor?
I've also looked at sistering joists but with a lot of obstructions, such as gas, electrical and plumbing lines in the way, it's not looking very practical. The total length between the exterior wall and I-beam support is around 12 feet. Any insight would help...thanks in advance!
2/8/2021 at 12:25:57 PM
Alex, I would suggest blocking between the joists with solid blocking, not just the cris-cross supports that I see in the pictures. This will add strength to the joists but also to the flooring above. Sistering will also help. I would be careful not to cut or remove any existing joists as they are already fastened to the sub-floor and are part of the structure. You might also look are re-screwing the sub-floor OSB down from the top (google how to do this) and this a\can assist the bouncing.
2/9/2021 at 3:07:05 PM
It appears to be 2" x 8" floor joist over an approx 20 ft. Span.
Too big a span for a 2 x 8!
Best to remove all blocking, sister all joists, being careful to only nail to the joist, not to the floor.
Then add blocking to further firm up the floor a partially address the twisting.
Best,
Andrew
416 504 9455
Partex Design Build Ltd.
2/9/2021 at 7:13:40 PM
2x8" @ 12" centers are capable of spanning 13' so you should be OK there. No simple solution without making a mess and removing the plumbing & electrical.
Some of the poorly installed cross-bridging could be re-aligned as it's not being very effective. It should have been nailed at the top prior to installing the floor sheathing. Solid blocking is also an idea
If you're able to remove the nails at the bottom without damaging the bridging you could maybe predrill and install screws as an improvement.
2/13/2021 at 8:06:36 AM
This is standard blocking and your floor joist are not to out of wack (twisted more than is expected)your span is fine for 2x8. If your floor is bouncy you got me, this normally occurs with over spanned osb I beams.
You can stiffen the floor by installing 2x6 or 8 solid dry!! blocking (sitting for 8 to 10 weeks alone) to replace existing, 4' center staggered, and glue them to the osb above with PL, but you must cut your blocking to match the joist angle as close as possible. Trying to square dry joist is a very bad idea unless you are replacing all your flooring. Last before you do all this check were the bounce is coming from could be (but not likely)that your joist are not sitting on the beam right.
Hope this helps
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