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Subfloor Preparation Inspection Checklist: What to Check and Photograph Before the First Plank, Board or Tile Goes Down
Flooring & Tile
The Subfloor Checklist: Twenty Minutes With a Straightedge and a Phone, the Day Before the Flooring Hides Everything for Twenty Years
Every floor covers the thing that decides whether it lasts. The day the old floor is up and the new one is still in boxes is the only day you can see the subfloor, measure it, and photograph it, and it is the day most homeowners are at work. Be there. The list below is what I check on my own houses before any flooring crew opens a box, and what I want in the photographs if there is ever an argument about whose fault the gap is. None of it needs a tool you do not own, except a 10 ft straightedge, which is a straight piece of aluminum from the building supply.
The numbers to have in your pocket
| Check | The limit | Applies to |
|---|---|---|
| Flatness, hardwood and vinyl plank | 3/16 in. in 10 ft | Any plank floor, nailed, glued or floating |
| Flatness, large-format tile | 1/8 in. in 10 ft | Any tile with a side 15 in. or longer; 1/4 in. for smaller tile |
| Concrete moisture, in-situ probe | Under 75% RH | Vinyl plank, glue-down anything, engineered hardwood over a slab |
| Concrete moisture, calcium chloride | Under 3 lb / 1,000 sq ft / 24 h | Same, where the sheet still uses this method |
| Wood subfloor moisture | Within 4 points of the flooring (2 for wide plank) | Nail-down and glue-down hardwood; subfloor itself under about 13% |
| Room conditions | 35 to 55% RH, 18 to 29 C | Everything, before, during and after; 48 hours before any moisture test |
| Acclimation | 5 to 7 days at living conditions | Hardwood; check the sheet for vinyl and laminate, usually 48 hours |
| Subfloor for nail-down hardwood | 3/4 in. plywood or 23/32 OSB | Joists at 16 in.; thicker or an overlay at 19.2 or 24 in. |
| Expansion gap, hardwood | 1/2 to 3/4 in. | Solid and nailed engineered, at every wall |
| Expansion gap, floating floors | 1/4 to 3/8 in., T-mould every 30 to 40 ft | Vinyl plank, laminate, floating engineered |
The walk-through, in order
- Is the old floor all the way out? Every staple from the carpet pad, every bit of old adhesive, every nail head. Staples left in plywood telegraph through vinyl plank as a thousand little dots; adhesive left on a slab stops the new adhesive from sticking. Photograph the floor from each corner.
- Walk it and listen. Every squeak is a loose sheet or a nail that has let go. Mark each one with a crayon. Screwing the whole floor at 6 in. along every joist is in the $0.75 a square foot minor prep rate and it is the best money on the job.
- Straightedge every room, both directions. Mark anything you can slide a quarter under (about 1/16 in.) for tile, a nickel (about 3/32) for plank; two nickels is the 3/16 limit. Photograph the straightedge with a tape in the gap at the worst spot in each room. That one photograph has ended more arguments than any contract.
- Check the sheathing at the wet spots. In front of the dishwasher, around the toilet flange, at the patio door, under the old fridge. Press with a thumb; soft or dark OSB gets replaced at $6.00 a square foot, and you want to know now, not when the tile setter finds it.
- Get the moisture numbers. On concrete, the probe reading with the date and the meter in the photo. On plywood, a pin meter reading on the subfloor and one on a plank out of the box, both in the photo. If the installer does not own a meter, that is information.
- Check the room, not just the floor. The furnace or heat is running, the windows are in, the drywall is painted or at least primed and dry, and the hygrometer says 35 to 55%. Hardwood laid into a house that is still drying out from the drywall is a cupped floor in the making. Where flooring falls in the sequence in a new house.
- Is the material in the room? Boxes opened, stacked flat, in the rooms where they are going, for the days the sheet says. Hardwood: 5 to 7 days. Photograph the stack with a date. Acclimation is a whole page because installers skip it a whole lot.
- Vapour retarder on concrete. Poly across the whole slab, seams taped, up the wall behind the baseboard line. Photograph a seam and a wall edge. Under a glue-down there is no poly, so the probe photo is the proof instead.
- Doors and heights. Stack a scrap of the new floor and pad against each door bottom and each transition to the next room. Anything that will not clear gets cut at $25 a door, and a step between rooms gets a reducer at $35. Decide now who is doing both.
- Agree the layout. Which direction the planks run, where the pattern starts, where the T-moulds land. A floating floor in a 45 ft open plan needs a transition somewhere, and you want to pick the doorway, not find it in the middle of the living room.
What the prep costs, so you can budget the fixes
Minor prep, screw and sand, $0.75 a square foot across the room. Self-levelling compound $3.00 at an average 1/4 in. Grinding a slab $2.00. A 3/8 in. plywood overlay $2.75. Replacing rotten sheathing $6.00 on the area replaced. Poly $0.35. A raised panel subfloor in a basement $3.50. Every one is a line in the flooring cost calculator, and the levelling cost page works through a kitchen slab and an old upstairs floor.
A 500 sq ft main floor that walks through this checklist clean costs 500 at $0.75, $375, in prep. The same floor with a dished kitchen slab needs 150 sq ft of compound at $3.00, another $450, and a wet spot at the dishwasher, two sheets of sheathing, 64 sq ft at $6.00, $384. That is $1,209 of prep against about $3,000 of mid-grade vinyl plank. It feels like a lot on the day. It is a tenth of what the repair page costs for a floor laid over it.
The photographs that matter
If there is ever a claim, against the installer, the builder, or the manufacturer, the question is always the same: what was the subfloor like before the floor went down? Nobody can see it anymore. Your pictures are the only evidence, and the manufacturer’s inspector will ask for them. Take them in daylight with a tape in the frame.
The minimum set: each room from two corners after tearout; the straightedge at the worst spot in each room with the tape showing the gap; the moisture meter on the slab or the plywood with its reading legible, plus one on a plank from the box; the material stacked in the room with a dated newspaper or your phone’s date visible; a poly seam and a wall edge on concrete; the expansion gap at a wall with a scrap of trim held above it, before the trim goes on. A dozen pictures. In a new house under Tarion, those pictures are the difference between a defect the builder owns and a conversation about your humidifier; the warranty page explains why. Finished floors get their own check before final payment, on the workmanship inspection page.
Questions people ask
What should a subfloor look like before installing flooring?
Clean to bare plywood or concrete, no staples or adhesive, screwed tight with no squeaks, flat to 3/16 in. in 10 ft for plank and 1/8 in. for large tile, dry by the numbers on the manufacturer’s sheet, and at room conditions of 35 to 55% humidity.
How do I check if my subfloor is flat?
A 10 ft straightedge or a tight string line, laid in both directions in every room. Anything you can slide two nickels under (about 3/16 in.) fails for hardwood and vinyl plank; a quarter (1/16) fails for large-format tile. Mark the spots and photograph the worst one with a tape.
Who checks the subfloor, me or the installer?
Both. The installer should, and a good one does it with a meter and a straightedge before he opens a box. You should, because you are the one left with the floor and the photographs when he has moved on to the next job.
What moisture level should a wood subfloor be?
Under about 13% on a pin meter, and within 4 percentage points of the hardwood going on it, 2 points for planks over 5 in. wide. A new house that has just been drywalled is often at 15% or more, and the floor waits.
Do I need to acclimate vinyl plank?
Most sheets say 48 hours in the room at living conditions; SPC is less fussy than WPC or laminate. Hardwood is 5 to 7 days. Either way the boxes are in the room, not the garage, and the heat is on.
Price the prep before the floor
Walk the checklist, count the marks, and put the fixes into the flooring cost calculator alongside the floor. If you already have quotes and none of them say a word about the subfloor, the $99 review reads them against this list and tells you what is going to show up as a change order.
Sources and further reading
- National Wood Flooring Association: the installation guidelines every hardwood warranty points to: subfloor flatness, moisture limits, acclimation, fastening schedules and the radiant-heat chapter.
- Tile Council of North America: the TCNA Handbook methods for tile over wood, concrete and in showers, and the ANSI lippage and grout standards a tile setter is held to.
- Tarion warranty coverage: what a new-home warranty covers for flooring gaps, cupping, cracked tile and squeaks in year one and year two, and the Construction Performance Guidelines it measures them by.
