Help in North Carolina – 3/4″ Solid over a Concrete Slab
Q: We are building a new home in Western North Carolina, it is concrete slab on grade. No crawl space. We want to install 3/4 hardwood floor’s. What is the best sub-floor to install over the concrete? What is the best method to attach the sub floor? Thanks for your help.
Needs Help,
George in NC
A: George and I have traded email back and forth for a bit and with some great insight from Gene D., we have a good solution to George’s question. We found out the home is in the ground breaking stage and Gene had a great build based suggestion instead of gluing down directly to the concrete:
If I were building or intending to build a new home, I would make the necessary adjustments to accommodate such an install. That would include the installation of 2″ x 4″ cut in half to act as sleepers (glued and shot in place) on 12″ centers then the installation of exterior grade 3/4″ plywood, then resin paper followed by 3/4″ nail down. The cost on this is surprisingly close to the cost of the adhesive that would be required to make this installation.
Gene also mentioned how a glue-down install to the concrete with 3/4” solid would be toast if it got wet. Now the reason behind this is because of how much movement can occur in a 3/4” solid should the floor absorb water from a large spill, water heater bursting or similar incident where there is liquid beyond normal cleaning, the floor will move and warp. Glue down installs do not allow for much movement nor for a whole lot of breathing room as far as the floor is concerned.
The subfloor spec Gene suggested creates a breathable subfloor which will prevent movement and be sturdy to boot. George asked about the possibility of floating two layers of 3/4” plywood for a subfloor then nailing to that. This would be a big no no, as it is not stable nor is it safe in the unfortunate event of moisture occurring. Should something cause the floor to move (such as humidity, water spills, or temperature changes beyond the norm) the entire floor would move in panels as the subfloor moved below.
Another thing to keep in mind here is price. Glue down floors tend to be fairly pricey, and the treated plywood required for George’s floating idea also comes with a decent price tag. The sleeper set up, using treated lumber, is actually a fairly economical choice that, as an end result, will give far more stability and life for the floor as a whole. End result – if your building a home, this is a great way to spec the home and it won’t cost much more to do when its spec’d in at the beginning.