Subfloor Types in Tennessee Homes: Plywood, OSB, Board and Plank
Five pages on this site link here, because the subfloor decides what you can install and it is the line item most likely to move a quote. It takes about five minutes to find out which one you have.
How to check, in five minutes
The easiest access is from underneath. In a crawl space house you can see the subfloor directly: take a flashlight, look up between the joists, and photograph what you see. Failing that, pull a floor vent and look at the cut edge, or lift a corner of carpet in a closet.
While you are under the house, put a hygrometer down there and leave it for a week. The subfloor question and the crawl space question get answered on the same trip, and the second one matters more.
The four you will find
- Plywood, 3/4 in tongue-and-groove. The most common subfloor in Tennessee — the median home here was built in 1987, so this is the default assumption rather than the exception. It accepts everything: nailed hardwood, floating floors, and tile over backer board or an uncoupling membrane.
- OSB, 3/4 in. Standard in newer construction across Middle Tennessee. Structurally fine and it holds fasteners slightly less well than plywood, so a nailed solid hardwood floor over OSB wants a tighter nail schedule. Its real weakness is water: OSB that has been wet swells at the edges and does not recover, and it usually happens during construction rather than afterwards.
- Board subfloor, 1×6 or 1×8 laid square to the joists. Common in prewar houses, which in this state means the older parts of Knoxville, Chattanooga, Memphis and East Nashville. Boards run the same direction as the joists you would nail into, so a nailed hardwood floor over it usually needs an overlay first.
- Diagonal plank subfloor, laid at 45°. The older and better version of the same idea — the diagonal means new flooring can be nailed in any direction, and it braces the structure. It takes nailed solid hardwood and carpet directly.
What each one costs you
The subfloor rarely changes the material price and frequently changes the preparation price:
- Nothing if you have sound plywood, OSB or diagonal plank and you are nailing hardwood or laying carpet.
- An underlayment — around a dollar a square foot — over a board subfloor with gaps, or under a floating floor that needs a flatter base.
- A plywood overlay — two to four dollars a square foot — where a board subfloor is uneven, cupped or split. It also raises the floor by the thickness of the sheet, which shows up at doors and at the bottom stair riser.
- Backer board or an uncoupling membrane for tile, on top of whatever is there, and a deflection check before any of it.
An estimate, not a quote. These are planning ranges for Tennessee, not a quote. What you actually pay depends on your rooms, your subfloor and the material you choose.
The condition that matters more than the type
A soft spot underfoot is not a flooring problem, it is a subfloor or a joist problem, and covering it hides it rather than fixing it. In a crawl space house the usual cause is moisture from below over a long period — which is the same thing that cups hardwood, and the same fix. What to do under the house comes before the floor goes down, not after.
Can I install hardwood directly over a board subfloor?
Over a diagonal plank subfloor, yes. Over boards laid square to the joists, usually not — the new flooring wants to run perpendicular to what it is nailed into, and it would end up parallel. An underlayment or a plywood overlay solves it, and it should be on the quote rather than discovered on day one.
Is OSB worse than plywood?
Not structurally, at the same thickness. It holds nails a little less well and it handles water considerably less well. If the OSB under your floor has swollen edges from a wet build, that gets addressed before anything goes over it.
How do I know if my floor deflects too much for tile?
Walk it and watch a glass of water on a shelf; then, if it feels lively, have the joist span and size checked against L/360 for ceramic and L/720 for stone. Long spans and 2×8 joists over a crawl space are the usual culprits, and blocking or sistering is far cheaper than a cracked tile floor.