Help preparing floor for 1'x2' porcelain in a Deck House [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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10-27-2013, 08:11 AM
Apologies if this has been covered somewhere (though a quick search didn't find anything) - I own a 1960's 'Deck House', post and beam construction. The joists are 3 3/8" x 11" (actual dim) spaced 9' apart. Spanning these are T&G 2 7/8" x 5 1/4" (actual) crossmembers which are the subfloor (Pine, I think). These dimensions aren't covered in the Deflecto calculator. I am planning to put down large format 1' x 2' porcelain tiles. Most tile contractors have never worked with this kind of structure. One recommended putting down 3/4" ply to reinforce the floor (there's alot of deflection). Does anyone know if this, in combination with a decoupling mat like Ditra or Strata) will be enough? To further complicate the wife really wants electric radiant.

any comments appreciated - i'm sitting on a pallet of non-returnable tile and want to do this right (if it's a lost cause i guess the tile will end up on Craigslist though!).

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10-27-2013, 09:47 AM
I think you need to consult with a structural engineer to calculate the deflection of your floor. If your floor does not meet the L360 criteria, you need to figure out something other than tile. If the floor is not L360 adding plywood (or anything else) will not solve your deflection issues, only more joists will do that.

If the floor does meet L360, then 1/2" plywood over the planks will suffice.

11-02-2013, 07:08 AM
thanks Petr - i'm going to get a laser leveler and measure the deflection directly.

11-02-2013, 07:22 AM
Welcome, Stuart. :)

I'm guessing you're somewhere on the Left Coast, but putting that information into your User Profile is frequently helpful.

We see a similar construction out there pretty regularly, but yours is an extreme version. We'd first need to know the unsupported span of your nominal 4x12 beams to start, but even then I don't know if we've got anyone who can calculate the deflection of those subflooring planks at a nine-foot span.

You can try measuring the actual deflection, but I don't think you're accounting for the logistics of loading the floor adequately for such a test. In-place testing might tell you something, but I'm not at all sure what.

I'm in agreement with Petr that some mid-span support is about your only reasonable option to reduce deflection to a useful level.

My opinion; worth price charged.