Planning on laying tile in our house. We're putting down cement backer board, and then ceramic tile. The tiles are 7in x 20in.

My question is, should the tiles be placed so they are perpendicular with the floor joists, or can they be laid parallel to the joists?

  • Is there something about the floor that makes the direction of the joists apparent? – JPhi1618 Mar 12 '18 at 14:47
  • I can go down in the basement and see what direction they are going. The reason I ask is a friend was telling me that with putting down hardwood you want to go against the direction of the joists to minimize sagging. He didn't know if the same was true of tile, especially if using backer board. – AndyD273 Mar 12 '18 at 14:49
  • Well, what I was really asking was if there are visible ripples or warping in the floor that are so bad you can see where the joists are. Like is the subfloor in bad shape or already sagging. – JPhi1618 Mar 12 '18 at 14:51
  • @JPhi1618 The subfloor does not appear to be in bad shape, though I do need to pull up the existing flooring. I have a few weeks until the tile arrives, so I haven't torn up the carpet/laminate yet. – AndyD273 Mar 12 '18 at 15:05

Your subfloor should be rigid enough that joist orientation isn't a factor in your flooring design, be it hardwood or tile.

Follow the specifications of your mortar manufacturer, or go with 3/4" solid boards, plywood, or OSB plus 1/2" plywood or cement board as a minimum.

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  • Ok. The house is only around 15 years old, and while I haven't had a chance to double check the thickness of the plywood I believe it is 3/4". I was planning on going with 1/2" cement board. I wasn't sure if I could get away with 1/4" as a way to avoid raising the floor level too much or not... – AndyD273 Mar 12 '18 at 15:10
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    Most mortar manufacturers want 1-1/4" minimum. If you happen to have 16" joist centers (unlikely), you could maybe go with 1" subfloor. – isherwood Mar 12 '18 at 15:11
  • I agree with 1-1/4" especially for large tiles if your base is not solid the tiles may crack. When I have limited thickness I will usually trowel some thinset under the backer to provide a little better base and screw it down well.+ – Ed Beal Mar 12 '18 at 16:38
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    The thickness of the cement board is supposed to be irrelevant. Meaning, it does not add any stiffness to the floor; this is what I have read in manufacturer's literature. It is only the wooded framing & decking system which provides required stiffness. – UuDdLrLrSs Mar 13 '18 at 0:24
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    Then why make it in half inch at all? – isherwood Mar 13 '18 at 1:37

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