I'm looking for feedback on a possible solution to a vexing problem. I'm having to replace the 2X4 sleepers (laid flat on a concrete slab) on a section of an existing oak floor built in 1951. Problem is, the 2X4s under the existing floor are 1/4 inch thicker than today's 2X4s. Would it be okay to make up that difference with 1/4-inch Hardie plank? In other words, lay the Hardie planks underneath each 2X4, then attach them both to the slab with Tap Cons or some such.

I would appreciate any thoughts on this idea, even if it's just a thumbs up or thumbs down.

Thanks.

You an use a cementitious shim like Hardie board to shim up the new screeds so they match others, or to make the correct height. Are the sleepers treated? In the old days no moisture barrier was common. You may use a special concrete sealer or lay 6 mil plastic sheeting over the concrete to cover new practices, or building requirements depending on your location, before laying the screeds if the concrete is exposed. You don't need to use a continuous strip of Hardie , just a piece every foot or two If the concrete is exposed, This helps to keep the floor flat, skipping bumps, as the screeds are laid. You can use a suitable glue to hold everything together besides the tap-cons for extra strength. Moisture curing urethane glues are the best.

Thanks for the feedback. I ended up not using Hardie board. After posting my question yesterday, I read that JamesHardie says that their product is not designed for use over concrete. Whether that applies to using Hardie board as part of a subfloor, I don't know, but it was enough to deter me from using it that way. So I went back to my original plan, which was to pour a 1/4 inch of self-leveling concrete over the repair area. That turned out to be much less difficult than I expected.

Yes, the sleepers are treated, and kiln-dried. I'm glad that you mentioned that moisture barriers were not common in the old days since I was wondering why the builders didn't put a barrier on this floor. I should say that the lack of a barrier does not seem to have caused any problems (the repairs I'm making are due to a leak from the attic), although I do plan to put a barrier over the repair area.

Any other tips or cautions? Thanks again.