I am also considering porcelain tile over a wood porch structure with a few modifications. My porch is over a basement area so will not be exposed to the weather on the underside. I am thinking of 2x6 KD joists at 12" OC with an 8 foot span. Then a layer of 3/4" exterior grade plywood with a layer of rigid insualtion board over that. Then cement board or 1/2" tile backer board, with the final tile installation over this, using epoxy grout. I'm hoping the combination of using this over an enclosed basement with the added insulation board will minimize any movement in the structure. May consider using the redguard material as well direclty below the tile backer board. Any thoughts?
Last edited by skurtz; 08-26-2010 at 10:31 PM.
Given that the span is only 8' the 2X6's are acceptable though I would prefer to see a beefier 2X10 as this will nearly stenghten the decking 3X limiting deflection. Don't forget to make sure you have an adequate slope tp shed water.
The 3/4" exterior and 1/2" cbu will work though do you experience freezing temps?
If so I would rather replace the 1/2" cbu with 3/8"-1/2" ply with ditra.
Remember to lay the grain of the ply perpendicular to the joist or you are asking for deflection.