My condo building in Boston was built in 1905, and converted from a hotel in the 1950's. Repairing some damaged hardwood in the livingroom the contractor found that the hardwood was nailed directly to the joists, no subfloor of any kind. A surprise!
At the opposite end, a hallway has a sloping floor, side to side, which I would like to correct. I am loathe to try to 'match' the color of the original with new (nailed to sistered, leveled joists), and don't have the height necessary to add subfloor plus new topping (tile or wood) as the front door swings over the sloping floor, one on each side.
The question: I have thought of pretending the hardwood floor is the subfloor, shimming it with purlins every two inches (yes, correct), and screwing concrete board to that and then setting tile. (I think I have height just for that, but not for subfloor, floor, backerboard, then tile.) Do-able?
I'm guessing this is a terrible idea, but it's all I can think of. I can shave the closet door (on the downslope side) but not the other door, which is the front door to the unit, is metal, and can't be easily altered. I'd love to bring up the original hardwood, sister the joists to level, then put the wood back down, but I suspect I will lose a lot in the process and don't want it to look like a patch job.
Suggestions, even brickbats cheerfully accepted. (Note: area is an entrance hallway, about 12'x4', sagging in the middle and level at both ends, and typical of older buildings in the area. 5th floor, can't "jack up" the building.)
Best Answer
Not doable at all.
Old houses have 3/4'' thick wood planks as subfloor, not 8x4 sheets of plywood like today's houses, so I would say that it's ok to consider your hardwood floor the subfloor. That's if you're putting another wood floor on top.
However, for the purpose of tiling you need an additional layer of plywood to reduce deflection that will cause the grout to crack eventually. And on top of that you would install your cement board. The cement board itself provides no structural support and is only used as a decoupling between a wood subfloor and the tiles, so the lateral movement of the wood is not going to cause the tiles to pull up. You can always use a durock membrane to reduce thickness, but you still need a floor that will not deflect.
If you really want to do this right you would take out the old floor down to the joist and install some OSB and then do what you want...