I have 2x8 (7.25x1.5) what appear to be doug fur or southern pine floor joists on 16" centers in a finished basement. I want to tile a master bath on the main floor. Joists span exactly 11' 4" from the concrete foundation to a steel center beam. Is that span too much?

If I use this calculator: http://www.johnbridge.com/vbulletin/deflecto.pl

I get 11.5 foot = not good for tile. 11 feet = good for tile.

House was built in 1962. My joists are in good condition, but subfloor is shot and will be replaced (had some leaky upstairs bathrooms.) However, the cross bridging is non-existent (should I add this?) And, in one joist someone cut a 1x3" notch out of the top for plumbing.

Can these joists / spans support ceramic tile? And, how large of a soaker tub will they support (soaker tub will be placed near outside wall/foundation).

1 Answer 1


I'm not sure if laminating a sister to each beam would count as three inches (I don't see why not if done properly, for at least as far as deflection is concerned; load calculation I have no idea), then it would be 3 x 7.75, and according to your link (L/673) that's OK for tile.

12 feet of 2x8 is pushing it, for sure. Sister each beam and install blocking.

My answer here, provides what insight I have for laminating beams; e.g., nailing schedules.

  • Interesting... This link says i'm good to go: awc.org/calculators/span/calc/timbercalcstyle.asp I'm obviously on the fringes. Laminating a beam (sistering) would be almost impossible cause the basement is finished. There's wiring and junk everywhere. The upstairs is finished as well, although I am tearing out about half of it. I'd only be able to laminate half the span. I think I'm going to go with what i've got and install blocking like you said. I'll have to laminate the part they notched I suppose.
    – maplemale
    May 6, 2015 at 23:56
  • @maplemale To tell you the truth I don't bother with these equations. If my 130lbs makes the subfloor bounce, then we need to do something about it, otherwise just take all the necessary steps for doing tile. Not very scientific, but if I can make it bounce without even jumping, it's no good. Less than L/360 violates product guarantees; doesn't mean it will crack at L/340.
    – Mazura
    May 7, 2015 at 0:21

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