Hello
I live in a bi level home that was built in 1962. When remodeling our lower level, I found that, while pulling down the drywall ceiling that there is no joist bracing what so ever. There is signifigant joist deflection and bowing, about 2 in at the lowest point. I wanted to run this by you guys to see if I plan to do it right. First I plan to pull up the old hardwoods (they need to be replaced anyway) and the subfloor on the main level. Then I will purchase new 2×8’s and sister them to the old joists with PL and nails to create new and level joists then replace the subfloor with PL and floor screws. Then of course install new 2×3 cross bracing onto the joists every 4 feet.
Am I missing anything?
Thanks
Replies
Are you saying
there is a 2" sag in the floor, or that one or more joists have bowed laterally by 2"? What species and grade are they, and what's the span?
In general, whatever the case, you need to frame the floor using a span table. I would not simply assume that sistering will work. It's a very easy engineering question to answer.
And, if you sister, you will need to jack everything back to level BEFORE nailing the sisters.
2" sag in the floor. Species
2" sag in the floor. Species is unknown. They are 2x8x12' span @16"oc. From the front to the middle of the house, there is a 2x8x12 supported at its end by a steel I beam with teleposts and the same from the middle of the house to the rear of the house. The area in question is open with no walls so jacking the joists back to level is not an option as the joists would lift off the beam and lift the floor. Which is why I wanted to sister a additional 2x8x12 to each joist making it level.
Ouch!
I would get rid of the old joists entirely, install 100% new. You are going to be fighting the sag and the wood has long-term memory.
You can't frame without knowing the species and grade you are using. Is #1 Doug Fir s-dry available in your area?
I thought about replacing the joists but... The joists are definatly one of the harder softwoods but they measure true 1 1/2 x 7 1/8 not 7 1/2 , which is what new lumber measures. I guess there was signifigant shrinkage back in 1960. So I would have to rip 3/8 off all the new joists. There is the possibility of notching 3/8 out of the 2x8 at the top plate and the I beam? what do you think? All of our constuction lumber up here is spruce, not sure of its rating. Our building codes state that 2x8's are good for up to 16 foot span. I know we have stupid codes. When ever possible I try to over build. Not sure if Douglas fir is available at our regular lumber yards but I will look into it.
Do not notch
the joists where they bear, or in any way that is not covered in the code as a prescriptive method for boring or notching.
The only code reference I have close by is the 2006 IRC. The span table for live load=40PSF, deflection=L/360, dead load=20PSF shows select-structural spruce-pine-fir as OK to span 12'-7" if spaced at 16" O.C. Select-structural is the BEST case, everything else (#1, 2, 3) is worse. For comparison, if you get select-structural Doug fir-larch you get 13'-7" span
Those values will give you an absolute code-minimum floor, something I would never build. You would be much better off with spans of 10 feet or less.
Something's wrong here. You had 2" of sag, which borders on catastrophic in my book. Maybe some of the lumber had an ugly crown to it the day it was installed, I dunno, but I would proceed with caution and make absolutely sure you solve whatever the problem is. If it were my job I would throw this one at the engineer, and he would probably spec something other than sawn lumber.
Sometimes bad sagging occurs in one area because construction materials (especially drywall) were stacked in that area during construction.
Ya good plan, I think an engineer would be my best bet. Thanks for the suggestion and thank you for your help.
Cheers.
Back in the 60s there was a period when lumber sizing kinda got out of control -- new lumber was found to have mysteriously "shrunk" 1/4" in the time it traveled from the sawmill to the lumber yard. Up until that time sizing was a bit "loosey-goosey" and was apt to be oversized rather than under. But the bean counters at the sawmills "overachieved" and cut things too close, forcing some standards to be imposed on the industry by about 1970.
What?
is the span of these floor joists? A 2 inch sag is quite a bit. You'll need to bring up the old b/4 fastening the new to them, a jack and post can do this. Be careful, are there walls on top of this floor?
Bridging is good, but every 4 ft is a bit of overkill. Certainly won't hurt your efforts. How much it helps is ?
If the OP does as he states and lifts the floor from the top and sisters, there would be no need to "bring up" the existing joists (and in fact it would be a bad idea). (Though this ignores the fact that lifting the entire floor is apt to be far more work than he anticipates.)
However, the point is well made that if there's 2" sag then the existing joists are likely undersized, and simply sistering the same size would be unlikely to permanently cure things. At **least** a step up to the next size joist is indicated.
And, to the OP: Bridging will reduce localized sag/bounce (one or two joists), but will not add substantial stiffness across a number of joists (eg, where 6-12 joists have sagged together).
Whelp
If it's a bi-level (NTTAWWT).........
Then there's the problem with that sag protruding onto the ceiling below.
Perhaps it's got a drop ceiling on that lower level.
And/or, if not-I think I would think about cutting the ends of the sistered joists (or not due to the pockets of the ends of the joists-could pocket the larger size joists if he'd like)........cutting them properly-no over cuts and tapering them at an angle up from the bottom-blocking them to support the ceiling level.
With the span, they're not drastically undersized-a 2" crown would have been huge in dry timbers- but I suppose one inch up and one inch down on a bunch of lumber might have been installed.
sorry, stink'n double post..................
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