What is the correct way to sister joists?

skellies

I'm doing some leveling of my floors and a contractor suggested sistering several joists to give more support in my kitchen and dining room. Also some of the joists have cracks.

I own a 1920 two-story, nothing fancy. I have to sister 10 2x8x16 joists in my basement. What is the best way to do this. Should I use some type of u-bracket made for sistering joists and nail that through the joists or will just nailing the new and old joists together be sufficient?

I'm in NY state. Thanks.

Big Dave

Around here all we do is glue and nail together. Be sure to raise the old joist to the proper position before attaching new one. I also assume you are going to sister with a larger joist for more support, I would.

Dave.

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MinConst

Big has the idea,
I jack the bad one to position, use some glue and screws and your all set. If the joists are bowed you may need to clamp them together to allow the screws to pull together. You can do allot with the new sister in regard to straightening the old. Fasten one end and use the leverage to move therm straight. Be sure to put the crown up.

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AtlanticWBConst.

What Big Dave said is good. That will defintely give you more support.

For cracked joists, especially in the areas where you might be adding more weight onto the floors:
Try 'sandwiching it' between 2 'sistered' joists with the nails and construction adhesive to hold it. Then you could drive lag screws or even carriage bolts all the way thru. This pulls it all nice and tightly together. You can alternate these (lags or bolts) near the top and then near the bottom of the sistered joist like you would on a deck ledger board.
We do that alot for sagging main carrying beams after we get them straightened, in order to keep them straight.

Big Dave

Skellies,after rereading your post you might want to consider a beam down the center to support the floor. 2x8 spanning 16 feet is not good. Around here 2x8 are only good for about 8 feet by code.

Dave.

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AtlanticWBConst.

Yeah....missed that minor point (16' span). Agree Completely with Big Dave...

skellies

Thank you all for the advice. To answer your suggestion, There is a beam running in the basement even though it is off center by 8 inches.

I was going to use new 2x8x16 to do the sistering. At home depot I saw 2x10's but that seemed to large.

But if I jack up and level before I put my sister joists in, will it then be a nightmare to get the new joists in there. Or do I just hammer them into place with a small piece of the 2x8's.

Big Dave

It's going to be a nightmare anyway. It should be easier to get the joist in if the old one is straight or has a slight crown. Just to make sure, your span is about 8 feet, right?

Dave.

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skellies

Do you mean the span/length of my beam or the length of my joists.

Big Dave

Length of joist. They need to be around 8 feet or less for a 2x8. It all depends on how well you want to do it. You can straighten and sister your joist, which will help with load bearing and straighten floor, but also I would check the beam under the joist for straightness up and down. If it's not straight then you can put more support under it or replace it with a new one. It all depends on how flat you want the floor and what you have to work with. It's hard to tell when you can't see pictures and of course as professionals we always figure the worst case scenario. Do what it takes to make you happy and satisfied.

Dave.

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