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Reinforcing/sistering joists in basement ceiling

smoke_teff | Posted in General Questions on

Hey all,

I’m finishing the basement of my Philadelphia row house and I’m wondering whether I should add some reinforcement for the exposed joists overhead before installing any ceiling material. 

The joists appear to be quite old (the house is about 65 years old), though not cracked, rotten, crumbling, etc. Just not new. There are no structural issues on the first floor–no real sagging, bouncing, squeaking, etc. The joists run every 16″ on center, supported at either end of the 12′ wide basement. 

Sistering the joists would just be a precautionary measure because of the age of the wood–and to avoid having to rip out any of the material I’ll be adding in the near future. Does reinforcing the joists seem wise? Or unnecessary? 

Another question…
The grooves the ends of the joists are currently resting are parged over and don’t allow any extra room for the sister joists. Would it still significantly reinforce the strength of the existing joists if I added boards the width of the basement and screwed them in, but the ends didn’t actually rest on any stone or ceiling plates? 

Thanks for any advice!

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Replies

  1. seabornman | | #1

    Yes you would add strength to the joists without extending to bearing points. You could even sister just the middle 2/3 and accomplish nearly as much stiffening as doing the whole span. 65 years is not that old, if especially if everything has remained dry and undamaged. I'd probably use a nail gun if I were doing it.

  2. Expert Member
    BILL WICHERS | | #2

    Old wood is often actually stronger than new material since the old wood tended to be denser. You didn’t mention the size of the existing joists (aside from the length), so we can’t know if they’re ok for the 12 foot span or not. Chances are if your floor is solid and not bouncy you’re probably ok. Sistering the joists won’t hurt though if you’re worried, and you don’t have to get all the way to the ends (although I’d probably notch the ends a bit to make them fit).

    If you sister the joists, use some construction adhesive (I like PL Premium for this) on the face to glue the the new joist to the old one. Use some screws to clamp the two together for the glue to set properly. You would normally also nail the two joists together, but it’s not really necessary if you glue and screw them together and the new joist runs all the way to the ends and is supported there.

    You can also glue and nail a 2x4 “sideways” along the bottom edge of the old joist to add strength. This makes a sort of DIY version of an I beam, but works best with dimensional lumber of standard dimensions so it doesn’t always work on old lumber. You’ll loose a bit of ceiling height this way too.

    Bill

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