Flooring Tile - Ceramic tile subfloor

I hope to install 12X12 ceramic tiles in a 2nd floor bath that's about 80 sq ft. I've read all the rules about joist and beam support in previous posts. I've got a vague idea of how important stiffness of the sub floor is. These rules seem to apply to standard built homes. Problem is that I've got a 3 level A frame log home here. It's built like a brick sh*t house, very solid. The 4"X8" ruff cut eastern white pine joists on the 2nd level are 24" OC. The rough cut eastern white pine 12"x6" beams span varies at 16' from center out to 7' on the ends.

The subfloor (which doubles as the first floor ceiling) is 2"X6" tongue and groove yellow pine. The subfloor is straight and level with no high or low spots. The only problem here is I don't want to raise the height of the floor much more than 1inch. Can I put down ceramic tile over hardiboard backer that is thin set to the tongue and groove sub? Do I need to add ½” plywood for extra stiffness then the hardiboard thin set onto that?:wall:


Any help here is well appreciated.

What you have for a floor is sufficient for 1/4" hardie backer and your tile. I have built log homes similar to what you have, and you could drive a tank on the second floor. I used v-joint T&G upside down, so it was a little more decorative on the lower floor.

No cement board or fiber cement boards I know of can be used over 24" centers. At least thats what the manufacturers state. That doesn't necessarily mean your tile installation will fail though.

I would suggest that you install 1/2" of thicker plywood, and then Schluter Ditra (a 1/8" thick isolation membrane). The end result will be a little more than 1" in height assuming a standard thickness tile. Ditra can be used over 24" centers with 2 layers of plywood, or planks and a layer of plywood.