Installing a T&G plywood subfloor comes down to five things: run the panels perpendicular to the joists, stagger the end joints, glue every bearing surface, tap the tongues home without damaging them, and leave 1/8″ at the panel ends. Get those right and the floor will be quiet in ten years.
Here’s the full sequence.
Before you start
Check the joists are flat. Sight down each one. Crowns all go up, and anything more than about 1/4″ out over the run needs to be planed or shimmed now. A subfloor telegraphs everything underneath it, and you cannot fix a humped joist after the panels are down.
Let the panels acclimatize. Sticker the bundle flat in the space, out of the weather, for a couple of days if the schedule allows. Panels delivered off a cold truck into a heated shell will move, and they’ll move after they’re fastened if you don’t give them time.
Snap your first line. Measure off the rim joist at both ends of the building and snap a chalk line at 48″. Don’t trust the rim to be straight. It usually isn’t, and a first course laid to a bowed rim throws off the whole floor.
Know your fastener schedule. For most residential subfloors: ring-shank nails or purpose-made subfloor screws, 6″ on centre along panel edges, 12″ in the field. Confirm against your span rating and local requirements. Our guides on what nails to use for a plywood subfloor and what size nails for 3/4″ plywood subfloor cover the sizing.
Step 1: Set the direction and the first row
Panels run perpendicular to the joists, with the 8′ length crossing the framing, the long edges parallel to the joists. That way each panel bears on at least five joists at 16″ o.c., and the T&G edges do their job on the unsupported long seams.
Start the first row with the groove edge to the outside wall and the tongue facing into the room. That leaves you a clean tongue to work against for every course after it. If you start the other way you’ll be fighting the layout the whole way across.
Rip the tongue off the first row’s outboard edge if it interferes with the wall line, since that edge is landing on the rim joist anyway, so it doesn’t need the profile.
Step 2: Glue as you go
Run a continuous 1/4″ bead of subfloor adhesive on every joist the panel will bear on. On seams where two panels meet over a joist, run two beads so each panel gets its own.
Only glue what you can cover before it skins over. In summer that’s two or three panels. Adhesive that’s tacked off isn’t doing anything. You’ve just made a mess and bought yourself nothing.
Some crews also run a light bead in the groove itself. It helps with squeaks, but it makes the panel much harder to seat, and if you overdo it the adhesive won’t let the joint close. If you do it, keep it thin and keep it in the bottom of the groove.
Glue is not optional if you care about squeaks. Nails alone will let panels move against joists as the framing dries, and that movement is the noise.
Step 3: Seat the panel
Set the panel with its groove over the previous row’s tongue, angled slightly, then bring it down.
To drive it home, use a knock block: a scrap of the same T&G with the groove facing out, or a purpose-made block. Never hit the tongue directly with a sledge. A mushroomed tongue won’t seat on the next course and you’ll be cutting the panel down.
Work along the seam in sections rather than trying to close the whole 8′ in one spot. Tap, move a foot, tap again. If a section won’t close, stop and look. Usually there’s a chunk of adhesive, a sliver of debris in the groove, or a proud nail. Force never fixes it.
Step 4: The 1/8″ end gap
This is the step people skip and regret.
The T&G long edges are self-spacing, so the profile sets the gap for you. But the panel ends need 1/8″ of clearance. A 16d nail laid flat in the joint is the traditional gauge and it’s close enough.
Skip it and here’s what happens: humidity comes up, the panels expand along their length, there’s nowhere to go, and the ends push up into a ridge you can feel through the finished flooring. It shows up months later, usually in the first humid season, and fixing it means pulling flooring.
Same at the perimeter: leave a gap where the panels meet the wall framing.
Step 5: Stagger and fasten
Stagger end joints by at least one joist bay. A 4′ offset from the previous row is standard. Never line end joints up across rows; that creates a continuous seam right through the floor.
Fasten as you go, don’t leave it. Edges at 6″ o.c., field at 12″. Keep fasteners about 3/8″ in from the edges. Closer and you’ll blow out the tongue or the groove wall.
If you’re using screws, set them flush, not countersunk deep. Overdriven fasteners crush the face veneer and give you a dimple that shows through thin finished flooring.
Check with a straightedge as you go. It’s much easier to pull one panel now than to level the whole floor later. If you’re already past that point, how to level a floor with plywood has options.
Step 6: Protect it until the roof is on
Subfloors sit exposed. Sweep standing water off, don’t let it pond in low spots, and don’t let debris sit on the deck through a wet week.
Even Exposure 1 panels will swell at the edges if they stay wet. If your build schedule has the deck open for a long stretch, a roll-on subfloor sealer is cheap insurance, or spec a panel that’s built for it. Pressure treated plywood is worth pricing for floors over crawlspaces and anywhere that stays damp in service.
The three mistakes that cause most squeaks
- No glue, or glue that skinned over before the panel went down. Nails alone don’t hold a floor quiet.
- Ends butted tight. Ridging, and it always shows up after the flooring is in.
- Fasteners missing the joist. Snap lines on the deck marking joist centres before you fasten. A screw driven into air holds nothing and works loose.
Add a fourth if you like: seating panels with a bare sledge. Wrecked tongues cost you sheets and leave you with seams that never quite close.
What to buy
Thickness is set by your joist spacing, not by preference:
| Joist spacing | Minimum | What most builders spec |
|---|---|---|
| 16″ o.c. | 5/8″ (19/32″) | 3/4″ (23/32″) |
| 19.2″ o.c. | 3/4″ (23/32″) | 3/4″ |
| 24″ o.c. | 3/4″ (23/32″) | 3/4″, 7/8″ for heavy loads |
| 32″ to 48″ o.c. | 1-1/8″ Sturd-I-Floor | 1-1/8″ |
Confirm against the panel’s own span rating stamp and your local requirements. The stamp on the sheet is the authority.
Why most crews go 3/4″ even at 16″ o.c.: 5/8″ meets code but flexes noticeably underfoot, and tile and engineered hardwood are both unforgiving of deflection. The upcharge is small against the total floor cost. If the finished floor is tile, don’t even consider 5/8″.
One naming note that trips people up: 23/32″ and 3/4″ are the same panel, as are 19/32″ and 5/8″. The fraction is the actual sanded thickness, the nominal is what everyone says out loud. In metric that’s roughly 18 mm and 15 mm. If your spec sheet and your order use different callouts, nothing is wrong.
And don’t forget the coverage width. Because the tongue is milled from the panel, a 4×8 sheet covers about 47-3/4″ once the joint is closed, not a full 48″. Over a wide floor that adds up, so plan 10% over your net square footage to cover it along with cuts and the stagger pattern.
Our tongue and groove plywood is a 3/4″ T&G CDX pine panel, which is the thickness most residential subfloors get built with and the one that covers 16″, 19.2″ and 24″ o.c. without argument.
If your long seams are landing on framing anyway and the profile isn’t buying you anything, square-edge CDX or exterior plywood does the same structural job for less.
Need a hand sizing panels to your joist spacing, or working out how many sheets the floor takes? Contact us with your dimensions and framing layout and we’ll spec it. For pricing on the full order, request a quote.
