I live on the third floor of a 1903 brownstone in Boston. The area at our front door was tiled with ceramic. The tiles cracked and I decided to replace them. When I removed the tile and cement board, I discovered that the cement board was attached directly to the old 1x8 plank subfloor. I would like to replace the tile with stone tile but I don't have ethe depth (only 3/4') to add plywood, cement board and tile. I assume the prvious tile cracked because the cement board was attached directly to the planks. Any suggestions? Thanks.

You're right, that old floor was installed all wrong, never had a chance.

Your new floor will be higher than the hardwood. The amount varies according to the specific tile and method you select. I'd recommend not going with stone since it'll require a much stiffer subfloor system than porcelain, and it's likely you'd have to stiffen the joists to get there.

So for porcelain, install good quality underlayment grade 1/2" ply, (prefer thicker ply like 5/8") Then spread thin set & install 1/4" cement backer then the tiles. Or, if you can find Ditra use it instead of cement backer, saves you about 3/16".

Fasten new ply with 1 1/4" flooring screws, do not use longer screws to hit the joists. Screw only to the planks.

Jaz