Information needed on replacing kitchen subfloor

lyren1970

We are in the middle of a kitchen remodel. I have the new cabinets (uninstalled). The quartz countertop is on order. I intend to install 12 inch porcelain tile. We have since discovered that the subfloor is shot. The house was built in the 50's and must have had hardwood floors throughout. At some point someone cut the floor out of the kitchen. The current subfloor is 5/8 in plywood over 2x4 sleepers on a concrete slab. The 2x4s are lying flat. (aprox 1.5 in high). They may have been glued down at some point but are currently free floating. The plywood is patched and uneven. There are multiple rotted areas. The room is 15 ft x 11 ft.

Our intent is to replace the subfloor from the concrete up. We would like the floor to be as close to even with the rest of the house as possible. The depth is 2 3/8 inches. I need to make sure that the deflection is adequate for the quartz countertop and the tile. I could put in a system similar to the existing one, but I need to know how far to space the sleepers and how frequent supports between the whole board need to be.

This is what I think we are doing:

1. Make sure area is clean and roll out roofing paper. (Does it matter if I use 15W or 30W?)

2. Rebuilding the sleepers - my understanding of this process is that you build a frame with 2x4s, then add more 2x4s spaced some distance apart. These would be run accross the 11 foot length of the room. I imagine that I need to add cross supports at some frequency between the 2x4s. These will be glued and screwed down to the concrete. I know that I have to make sure that everything is level. Could I do this in four 5.5 ft X 7.5 ft sections? I would put supporting 2x4s approximately 11.5 inches apart, with additional support staggerd in between the 2x4s - alternating 2 braces (22 in apart) and 3 braces(16.5 in apart). I would then connect the modules and screw them to the concrete. See attached picture.

3. Add 5/8 in t&g plywood subfloor - glued and screwed down. (Which way should these be run in relation to the sleepers?)

4. Add 1/4 in hardibacker. I would prefer the 1/4 in because it will cause less of a transition between rooms. The hardibacker will be installed on thinset and screwed down.

Will this work?


Help!!!!

Attached Images

 

26yrsinflooring

Ditra is 3/16 and has uncoupling power Hardi will never have. It is lighter and much easier to work with.

I will let the other pros help you with the other steps.

angus242

Plywood is a structural part of the subfloor, Hardi (or any CBU) is not. With that in mind, I'd rather see you use 3/4" T&G and then Ditra. The height between either way should be almost identical. As 26 said, there are more pros for Ditra than CBU.

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Angus

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