Span Calculator for Wood Joists

Discussion in 'Ceramic and Stone Q&A' started by Kman, Oct 5, 2011.

  1. Kman

    Kman Tile Expert I Support TFP Senior Member Published

  2. AlexWoods

    AlexWoods Member

    Thank you Kman
     
  3. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    What about the pier and beam that homes have with 4 foot centers, haven't read anything about that in NTCA manual .
     
  4. Kman

    Kman Tile Expert I Support TFP Senior Member Published

    Those are a birds of a completely different feather. :blink:

    Typically, the span is okay, as they usually don't span that far. Doesn't mean they won't, just that they usually don't.

    The problem with those is the spacing. The between-joist deflection is too great with 48" spacing. Many of them have 2x's as a subfloor, which means they normally need a layer of plywood on top, but they have to be done on a case-by-case basis. Usually, two layers of 3/4" plywood, properly installed, will do the trick for a ceramic installation.

    I would not encourage anyone to install natural stone over those. Not saying it can't be done, but the deflection would have to be so small that the amount of subfloor required would stack up so thick that nobody would want it. A 4x8 sheet of plywood would span only three joists. Maybe that's why many of them have 2x's for subfloor.

    Anyone with a pier and beam structure that is planning to invest a significant amount of money in a tile or stone installation should consider hiring an engineer to give them an opinion on the suitability of their joist system. :)
     
    Last edited: May 15, 2014
  5. kwfloors

    kwfloors Fuzz on the brain Charter Member I Support TFP Senior Member

    I think it would be cheaper to add 2x6 or 2x8 next to the 2x4 if you can than to stack up plywood on top. I saved that link and have borrowed it from K on a couple of posts. Handy, now its a sticky. :D
     
  6. Kman

    Kman Tile Expert I Support TFP Senior Member Published

    Maybe you could explain what you mean by that part. I was referring to 2x lumber lying flat across the joists, sometimes perpendicular, sometimes diagonally, serving as the subfloor.

    By the way, it's been a sticky since October 2011. I just haven't gotten around to the instructional class yet. :)
     
  7. kwfloors

    kwfloors Fuzz on the brain Charter Member I Support TFP Senior Member

    I was thinking the 2x4s were between the beams under the floor. :hmmm:
     
  8. Kman

    Kman Tile Expert I Support TFP Senior Member Published

    Occasionally you might see something like that. 4x6 beams run every 48" with 2x set perpendicular on top of it as the actual joist system.

    To be honest, I'm not really sure of the reason for pier and beam construction, unless it's simply a geographic thing. Most of them you'll see are on the west coast, maybe in the coastal areas, where they have to be far up off the ground. :hmmm:

    Seems like you could still make a good joist system with 2x10's or 12's on 16" or 19.2" centers. 48" is just too far apart and causes too many problems.
     
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