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Old 05-09-2012, 02:47 PM   #1
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Floor Flex with Car Deck / Post & Beam Construction


I am hoping to replace a linoleum floor with a tile one. However, our cabin has POST & BEAM construction with 2" x 6" TONGUE & GROOVE subfloor spanning the beams and I am wondering if we may have too much flex in the floor for tile.

The floor SEEMS very solid, but the 2" x 6" tongue & groove car decking subfloor spans 4" x 10" beams (supported by 4" x 6" posts on good concrete foundation) with a 60 inch span between the 4" x 10" beams (face to face). There is currently particle board on top of the car decking, which I understand I'll have to cut out and replace with 3/4" plywood (or thicker???), and I'm planning on using thinset and 1/4" Hardibacker on top of that. Will this be rigid enough? Should I use thicker plywood and/or 1/2" Hardibacker? Will I still have too much flex from the 60" spans? How can I tell?

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Old 05-09-2012, 04:41 PM   #2
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Floor Flex with Car Deck / Post & Beam Construction


Evaluation of stiffness of post and beam framing probably requires actual mathematical analysis of the floor joists and car decking, which is typically done using a computer program (I do my analysis using an Excel spreadsheet I developed). Be sure to evaluate stiffness along the beams and joists, and between the joists. Depending on the size of the tile, the required stiffness differs. The larger the tile, the stiffer the floor needs to be. Natural stone is the most picky, you generally need L/720 for natural stone tile.

The John Bridge website has some tools that may be applicable, not sure it covers large format beams.

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Old 05-09-2012, 04:52 PM   #3
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Floor Flex with Car Deck / Post & Beam Construction


Thank you! For whatever it's worth, we don't have joists at all. The 2" x 6" tongue and groove cardecking is mounted directly to the beams.

Our tile size is only 12" x 12"... (ceramic) since we couldn't find porcelain or stone that were appropriate.

Is this something any structural engineer can compute, or is it something you can compute for me?
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Old 05-09-2012, 07:36 PM   #4
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Floor Flex with Car Deck / Post & Beam Construction


Since you do not have joists, the beams are effectively joists at wide spacing. Any structural engineer can compute the stiffness, but you probably don't really need one, your tile installer may know how to do the computation. Or are you planning to put the tiles in yourself?

From the sounds of it, you have 2x6 decking spanning 5 feet. Is the decking full size, or is it dressed to perhaps 1-1/2 inches thick? Makes a big difference to the stiffness. If you give me the exact dimensions of the floor decking, and verify the span, and tell me the species of wood, I can give you an approximate value for the stiffness, then you can decide if you need to improve the subfloor prior to tiling.
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