Subfloor For Exterior Ceramic Tile?

Slowtrawl

Question. We are in the process of an addtion of garge with family room above. The family room has a 8'x25' covered deck off of it, above the garage below. Our original plan was to use a waterproof membrane flooring on the deck. Wife now want to go with a 16" ceramic tile. The area gets very little weather, maybe a small splash when it rains (which is all the time). The question is what kind of subfloor should I install? I was thinking hardi-backer. Should I also use a waterproof membrane between the hardi-backer and the plywood? The other challenge is the patio door threshold and siding come down almost to the deck. With some trouble we can cut the siding to allow some flashiong and then the tile can tuck under it. The sill is another issue. With the backer and tile, I am guessing we will be raising the floor height 3/4" or so. I don't like the idea of butting the tile into the threshold (aluminum), but short of tearing off siding, tearing out the doors and raising them an inch, I don't see any choice. If the deck wasn't completely covered, this wouldn't be an option. Any suggestions?

pscinteriors

If possible use 1" T+G plywood subfloor.make sure deck is running a 1/4" per foot slope.use Schluter Ditra for anti fracture membrane and waterproofing.Just make sure you buy the waterproofing seam tape for the ditra.The Ditra is only 3/16" thick and doubles as a membrane.Look it up on Schluter.com.
And Then Falshing,flashing,flashing.I have replaced alot of decks that were not properly flashed by the tilesetter.
Nick