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Old 08-30-2008, 11:09 AM   #1
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Sistering floor joists


We are sistering a few 2x10 joists that support our 2nd floor bathroom to help support a cast iron clawfoot tub. We have pulled out the kitchen ceiling below (badly stained anyway) and we see that we can set the ends of the sisters up onto the top plate with the old joists on both ends of the room (spans 13').

The problem is that old and new 2x10s are not exactly the same width, right? So is it more important that the bottom edge rests even on the top plate with the old joist, or that that top edges of the two joists are level against the floor up above.

Also, in a couple of places there is a bit of notching near the top of the joist that has to happen to help accommodate the tub drain. Should we get these new joists attached before or after the plumber replaces all the old pipe?

Thanks in advance!
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Old 08-30-2008, 11:40 AM   #2
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Sistering floor joists


Remember that whatever you put in there is better than what you have now. Since the new joists are not quite as deep, do whatever makes you happy because it won't really matter. I'd probably hold them tight to the floor, and shim them tight to the top plate at each end.

Do a good job of attaching the new joist to the old to get them working together. Nothing short of two horizontal rows of 16d nails at 12"oc staggered.

Sometimes notching is necessary. Try to avoid notching both joists wherever possible. Notches are allowed in the top of the joist in the outer thirds of the span, and no notches are permitted in the middle third. Notches are not to exceed 1/6 of the depth of the member in depth, and not more than 1/3 the depth of the member in length. Drilled holes are usually better than notches. Holes can be up to 1/3 the depth of the member provided they are at least 2" from an edge.

You need to have your new joists installed before your plumber shows up to run his lines and drain. That way he can drill holes instead of notch wherever possible.
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Old 08-30-2008, 01:47 PM   #3
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Sistering floor joists


Quote:
Originally Posted by thekctermite View Post
Remember that whatever you put in there is better than what you have now. Since the new joists are not quite as deep, do whatever makes you happy because it won't really matter. I'd probably hold them tight to the floor, and shim them tight to the top plate at each end.

Do a good job of attaching the new joist to the old to get them working together. Nothing short of two horizontal rows of 16d nails at 12"oc staggered.

Sometimes notching is necessary. Try to avoid notching both joists wherever possible. Notches are allowed in the top of the joist in the outer thirds of the span, and no notches are permitted in the middle third. Notches are not to exceed 1/6 of the depth of the member in depth, and not more than 1/3 the depth of the member in length. Drilled holes are usually better than notches. Holes can be up to 1/3 the depth of the member provided they are at least 2" from an edge.

You need to have your new joists installed before your plumber shows up to run his lines and drain. That way he can drill holes instead of notch wherever possible.
Well stated!!
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Old 08-30-2008, 02:12 PM   #4
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Sistering floor joists


When sistering joists, I use torx screws shot in from an angle down into the old joist, after confirming the old joist is level...doing one at a time, and screwing a pattern from the center out to the plates.....the point being to pull the new joist down and tight with the old...
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