Installing Plywood Over Plank Subfloor: Thickness & Steps

This post contains Amazon affiliate links. If you buy through them, ThePlywood.com earns a small commission at no extra cost to you.

No single plywood thickness works over a plank subfloor. The right one depends on the floor going on top. Plan on 11/32″ APA underlayment for sheet vinyl, 3/8″ or thicker for thin wood floors and parquet, and 15/32″ (1/2″ nominal) for tile and for hardwood running parallel to the joists. Gaps and fastener spacing also change with the flooring system, so follow the right schedule below.

Quick answer

Tile with an uncoupling membrane: 15/32″ minimum Exposure 1 plugged-face plywood or OSB, over planks at least 3/4″ thick
3/4″ solid hardwood across the joists, over diagonal planks: usually no plywood needed
Hardwood parallel to the joists: 15/32″ minimum plywood
Thin solid strip or parquet: 3/8″ minimum
Sheet vinyl / resilient flooring: 11/32″ minimum APA underlayment. APA’s 1/4″ panels are for smooth panel subfloors, not planks.
Gaps: 1/32″ for APA underlayment, 1/8″ between sheets and 1/4″ at the walls for Schluter’s tile assembly

Plywood Over Plank Subfloor Thickness Chart

Tile floor assembly showing plywood underlayment, uncoupling membrane, mortar, and ceramic tile over plank subfloor.

Finish floor	Plywood over planks	Source
Ceramic or porcelain tile (DITRA)	15/32″ minimum, Exposure 1 plugged-face plywood or OSB, over planks at least 3/4″ thick	Schluter detail D-SP-TS
3/4″ solid hardwood across the joists, over diagonal planks	None required	NWFA
3/4″ solid hardwood parallel to the joists	15/32″ minimum	NWFA
Thin-classification solid strip	3/8″ or thicker	NWFA
Parquet	3/8″ or thicker, nailed on a 6″ grid	NWFA
Sheet vinyl / resilient tile	11/32″ minimum APA underlayment, sanded face	APA
Carpet	Usually none if the planks are flat and tight	Pad hides small gaps
Floating LVP or laminate	None if the floor meets the flooring maker’s flatness spec; underlayment if the planks are cupped	Flooring maker

Warning: Plywood, a membrane and tile together can raise the floor close to an inch. Before you buy sheets, check door swings, the dishwasher opening, and the transition to the next room.

Check the Planks Before You Add Plywood

Plywood smooths and stiffens the surface between joists. It won’t fix bad planks or bouncy joists.

Thickness. Under IRC Section R503.1, board subfloor at 16″ joist spacing needs at least 5/8″ net thickness, whether the boards run perpendicular or diagonal. At 24″ spacing it needs 11/16″ for perpendicular boards and 3/4″ for diagonal. For tile, Schluter’s plank detail requires planks at least 3/4″ thick on joists no more than 24″ apart.

Condition. Look for rot near tubs, toilets and exterior walls. Look for cracked or split boards, and for board ends that don’t sit on a joist. Replace bad sections rather than burying them. If moisture is the cause, see wet and warped plywood first.

Moisture. Check both the planks and the new plywood with a pin meter. APA says to install underlayment only on a dry subfloor. NWFA caps wood subflooring at 12% moisture content. The difference between the subfloor and the wood flooring should be no more than 4% for strip under 3″ wide, or 2% for planks 3″ and wider.

Bounce. Jump in the middle of the room. If the floor flexes, fix the joists first. See how to stiffen a subfloor and reinforcing floor joists.

How to Install Plywood Over Plank Subfloor: Step by Step

1. Strip the room to the planks

Pull the baseboards, the old flooring and any staples or carpet tack strip. Set any nail heads that stick up above the planks.

2. Refasten the planks to the joists

Drive screws through loose or squeaky boards into the joists. Once the plywood is down, you can’t easily reach them again. If the floor already squeaks, start with how to fix a squeaky floor.

3. Flatten high spots

Plane or sand cupped plank edges and fill low areas. Tile has its own flatness limits. The Tile Council of North America (TCNA) allows 1/4″ in 10 feet for tile with edges under 15″, and 1/8″ in 10 feet when any edge is 15″ or longer.

4. Acclimate the plywood

APA recommends standing underlayment panels on edge in the room for several days so they adjust to the room’s humidity before you install them.

5. Lay out the sheets

Run the face grain perpendicular to the joists. APA says this gives the stiffest floor.
Stagger the end joints so four corners never meet at one point.
Keep the plywood seams off the plank seams.
Space the sheets to match your flooring system:
- APA underlayment for vinyl or resilient flooring: 1/32″ at all ends and edges
- Schluter tile assembly: 1/8″ at all ends and edges, 1/4″ at the walls and cabinets
- NWFA second layer for hardwood: 1/8″ between sheets

Staggered plywood sheets installed over an existing plank subfloor.

6. Fasten to the right schedule

Use the schedule for the floor you’re installing. If the flooring maker publishes its own schedule, follow that one.

Sheet vinyl or resilient flooring (APA underlayment over lumber subfloor, 11/32″ panel):

Check the price on Amazon

3d × 1-1/4″ ring- or screw-shank nails
6″ apart along the panel edges and 8″ apart each way across the rest of the sheet
Fasteners 3/8″ in from the panel edges
Nail length about equal to the combined thickness of the underlayment and the planks
Heads flush or just below the surface. Overdriven nails show through vinyl and cause squeaks.
APA advises against gluing the underlayment to the subfloor.

Tile over DITRA (Schluter, 1/2″ panel):

Ring-shank nails or wood screws. No staples and no drywall screws.
4″ apart along the panel edges and 6″ apart across the rest of the sheet
Fasteners must go through both the plywood and the planks, with as little as possible going into the joists

Hardwood second layer (NWFA double-layer spec):

Ring-shank nails or staples on a 12″ grid
Then follow the wood flooring maker’s instructions

For fastener basics, see nails or screws for plywood.

7. Prep the surface for the finish floor

For vinyl, fill and sand the joints so they don’t show through. For tile, install the membrane to its maker’s instructions, and see how to prepare a plywood subfloor for tile.

What You Need

Pin-type moisture meter: checks both the planks and the new sheets before they go down. Check the price on Amazon
Ring-shank underlayment nails or wood screws: smooth nails work loose as the wood moves. Under tile, Schluter rules out staples and drywall screws. Check the price on Amazon
6-foot aluminum straightedge: finds the high plank edges before you cover them. Check the price on Amazon
Uncoupling membrane (for tile): Schluter DITRA has a published detail for plank subfloors. Check the price on Amazon

Which panel:

Under vinyl: use panels stamped APA Underlayment or C-C Plugged with a sanded face. Our guide to underlayment grade plywood explains the stamps.
Under tile with DITRA: use Exposure 1 plugged-face plywood or OSB, not standard CDX.
Hardwood second layer: NWFA’s spec uses CD Exposure 1 plywood (CDX).

6 Mistakes That Ruin a Plank Subfloor Overlay

Using thin luan or standard CDX under tile. Schluter’s detail calls for 15/32″ plugged-face plywood or OSB. Use the wrong panel and you risk cracked grout and a voided membrane warranty.
Using 1/4″ underlayment over planks. APA reserves 1/4″ for smooth panel subfloors. Over planks, the board edges show through vinyl.
Using one gap for every system. A 1/8″ gap under vinyl leaves joints you have to fill. Butting sheets tight under tile lets the seams lift when humidity rises.
Skipping the plank refastening. Squeaks under new plywood can’t be fixed from above without pulling up the new floor.
Covering wet planks. Over a damp crawlspace, the planks can cup the plywood above them. Fix the moisture source first.
Ignoring the height change. The added thickness can leave doors dragging, a dishwasher that won’t slide out, and an awkward step at the doorway.

Cost Difference: Overlay vs. Tear-Out

A 12 × 15 ft room is 180 square feet, or about 5.6 sheets of 4 × 8 plywood, so plan on 6 sheets plus fasteners. Tearing out the planks means buying thicker structural panels for the same 6 sheets, plus the demo work and debris removal. An overlay is usually the cheaper route when the planks are sound. When they aren’t, the money you save on the overlay is lost when the new floor fails. Check local prices for both options before you decide.

When Not to Install Plywood Over Planks

The planks are thinner than the IRC Table R503.1 minimum for your joist spacing.
There is rot, insect damage, or a moisture problem that hasn’t been fixed.
The joists bounce. Fix the framing first.
You’re installing natural stone. Stone needs a stiffer floor than Schluter’s plank detail provides, so follow the membrane maker’s stone detail.
Floor height is already tight at the doors and next to the neighboring floors.

FAQ

What thickness plywood goes over a plank subfloor?

It depends on the finish floor. Use 11/32″ APA underlayment for sheet vinyl, 3/8″ minimum for thin strip and parquet, and 15/32″ (1/2″) for tile and for hardwood running parallel to the joists.

Can I install hardwood directly on a plank subfloor?

Often, yes. NWFA allows 3/4″ solid hardwood over diagonal planks when it runs perpendicular to the joists. If it will run parallel to the joists, add at least 15/32″ plywood first.

Can I use CDX plywood under tile over planks?

Not with Schluter DITRA. Its plank-subfloor detail calls for Exposure 1 plugged-face plywood or OSB, at least 15/32″ thick.

How big a gap do you leave between plywood sheets?

It depends on the system. APA underlayment gets 1/32″ at ends and edges. Schluter’s tile assembly gets 1/8″ between sheets and 1/4″ at the walls.

Should you glue plywood underlayment to the subfloor?

APA advises against gluing underlayment to the subfloor. For tile or hardwood, follow the membrane or flooring maker’s instructions.