Replacing deck joist - board width mismatch

[serge1966]

I am working on replacing decking and found a couple of rotted joist I decided to replace as well.

The joist size is 2x8-12. I purchased the replacement joists however when I took one rotten out and compared with the new one, it turned out the new one is 1/4" wider. The label on both old and new joists says 2x8-12, but the exact width of the old one is 7" and new one is 7 1/4".
Did I get wrong product? The old deck may be 10 years old -- is it just result of the wood shrinking over years? If so does it mean I can't replace a few joists and should do it for all of them?
Technically I could cut off the extra piece but if it is shrinking, then it will become uneven in a few years.

Any guidance would be much appreciated

[jteneyck]

Welcome to the Forum.

2 x 8's are supposed to be 7-1/2" wide, but it seems like they can be just about anything these days, but 7" does seem very narrow.  In any case, I would rip off the 1/4" on your new ones and replace only the ones that need to be.  If they end up shrinking you can always put shims under them where they cross the beams.  

John

[Roly]

I am working on replacing decking and found a couple of rotted joist I decided to replace as well.

The joist size is 2x8-12. I purchased the replacement joists however when I took one rotten out and compared with the new one, it turned out the new one is 1/4" wider. The label on both old and new joists says 2x8-12, but the exact width of the old one is 7" and new one is 7 1/4".
Did I get wrong product? The old deck may be 10 years old -- is it just result of the wood shrinking over years? If so does it mean I can't replace a few joists and should do it for all of them?
Technically I could cut off the extra piece but if it is shrinking, then it will become uneven in a few years.

Any guidance would be much appreciated

The 7 1/4" width for a 2x8 is correct.    Are the rest of the joists all 7" or was it just the rotted one ?  If all the rest are 7" I would trim the new one to 7"   Roly

[AUswimKC]

Is the new joist a wet new PRessure Treated? Then it will shrink. A Lot. Prob close to 7”. Maybe not all the way down to 7”. When I lay new PT deck boards I butt them tight together. I’m three months the gap is almost 1/4”

[Gary G™]

Joists aren’t deck boards.

[Snipe Hunter]

Joists aren’t deck boards.

But wet PT will still shrink.

Are the existing joists sitting in joist hangers or on a ledger strip?

[jteneyck]

The 7 1/4" width for a 2x8 is correct.    Are the rest of the joists all 7" or was it just the rotted one ?  If all the rest are 7" I would trim the new one to 7"   Roly

I didn't believe it until I looked it up but you are right, a nominal 2 x 8 has an actual width of 7.25".  Always thought it was supposed to be 7.5".  Now I know better.  Thanks. 

John

[Tapper]

Welcome to the Forum.

2 x 8's are supposed to be 7-1/2" wide, but it seems like they can be just about anything these days, but 7" does seem very narrow.  In any case, I would rip off the 1/4" on your new ones and replace only the ones that need to be.  If they end up shrinking you can always put shims under them where they cross the beams.  

John

If the joists are sitting on a beam couldn't you just notch it at that point to level it with the others? A little extra "beef" never hurts.

Doug

[Snipe Hunter]

I think we lost him. But I'd just notch the joist too and be done with it.

[Gary G™]

^^^^^^^^^^^^^ This ^^^^^^^^^^^