How to Install Wood Flooring: Nail, Glue, or Float

To install wood flooring, pick the method your subfloor allows, test the moisture and flatness of that subfloor, leave an expansion space at every wall equal to the flooring thickness, then lay staggered rows from a straight working line. Nail-down, glue-down and floating floors differ mostly in the prep and the fasteners, not in the layout. This guide uses the National Wood Flooring Association (NWFA) technical publication on installation methods for the numbers, and it corrects two figures that are repeated all over the web: the expansion gap and the flatness tolerance.

Whatever the manufacturer’s own instructions say overrides everything below. NWFA’s own text tells installers to follow the flooring and nailer maker’s directions first.

Pick the Installation Method First

The method is decided by what is under the floor. NWFA says a wood floor may be nailed over most wood subfloors, but not particleboard. Over concrete you are choosing between glue-down and floating.

Method	Subfloor it suits	Typical flooring	What to know
Nail-down	Plywood or OSB, or board subfloors that meet minimum requirements	Solid 3/4-inch and engineered wood	Needs a flooring nailer or stapler; the most traditional method
Glue-assisted nail-down	Wood subfloors	Wide plank (NWFA: over 5 inches wide, when site conditions allow)	Fewer fasteners per square foot on wide boards, so adhesive helps hold them
Glue-down	Concrete or wood, once tested for moisture	Engineered wood, some solid	Tighter flatness tolerance and a moisture test of the slab
Floating	Most flat, dry subfloors	Engineered wood and laminate	Boards connect to each other, not to the subfloor

If you are still choosing between wood, laminate and vinyl, our hardwood vs laminate vs vinyl comparison lays out the trade-offs, and our hardwood flooring price guide covers material cost before you commit.

Test the Subfloor Before You Buy Fasteners

NWFA calls moisture testing compulsory on every job and says never to install a wood floor over a known moisture condition. Test both the flooring and the subfloor. The subfloor numbers below come from the same NWFA publication.

Check	NWFA figure	What to do if you miss it
Flatness, nail-down on wood	1/4 inch in 10 feet, or 3/16 inch in 6 feet	Sand high spots, fill low spots, or re-sheet
Flatness, glue-down on wood	3/16 inch in 10 feet, or 1/8 inch in 6 feet	Level before gluing; glue shows every ridge
Concrete, calcium chloride test	Over 3 lbs per 1,000 sq ft per 24 hours	Wait for the slab to dry or install a Class I vapor retarder
Concrete, in-situ RH test	Over 80 percent	Wait for the slab to dry or install a Class I vapor retarder
Wood subfloor	Sound, free of squeaks and vertical deflection	Screw down squeaks; replace damaged panels

Flooring that runs parallel to the joists needs help. NWFA gives two fixes: add a second layer of at least 15/32-inch plywood over the existing subfloor, or add bracing between the joists, which it says a qualified professional should do. For the full decision between joist direction and room looks, see our guide on which way floor planks should run.

Tools and Materials

• Flooring nailer or stapler, rented or bought, for nail-down and staple-down floors
• Chalk line, tape measure and carpenter’s square
• Miter saw for end cuts and a table saw or jigsaw for the last row
• Mallet, tapping block and pull bar (the pull bar reaches the last row where a mallet will not swing)
• Wedge spacers for the wall gap
• Moisture meter, plus a concrete moisture test if the slab is in play
• Vapor retarder or underlayment if your flooring maker requires one
• Fasteners or adhesive to match the method; follow the flooring maker’s choice

Step-by-Step: Nail-Down Installation

1. Check the moisture and flatness of the subfloor against the table above, and get the flooring’s moisture reading too. Acclimate the flooring as the manufacturer directs, and judge it by meter readings of both flooring and subfloor, not by counting days.
2. Undercut door casings and jambs so the boards slide under them. Pull the baseboards if you can; the gap then hides behind trim.
3. Snap a working line parallel to the starting wall, set back by the expansion space. Runs should be straight to within 3/16 inch over 10 feet, because a crooked first row shows up as gaps in every row after it.
4. Lay the starter row along the whole line and secure it firmly. Face-nail it near the wall, since there is no room for the nailer there. NWFA’s schedule for face-nailing at a wall is an 18-gauge fastener about every 8 to 10 inches.
5. Blind-nail through the tongue once the nailer fits. For 3/4-inch solid planks and engineered wood 5/8 inch or thicker, NWFA’s standard schedule is a fastener every 6 to 8 inches along each board, 1 to 3 inches from each end joint, with at least 2 fasteners per board. Engineered boards thinner than 5/8 inch use a tighter 3 to 4 inch spacing, 1 to 2 inches from the ends.
6. Stagger the end joints. NWFA’s rule of thumb is at least twice the board width from row to row, so a 3-inch board needs a 6-inch stagger. Start each new row with the cut-off from the last one where you can, as long as the piece is at least 12 inches.
7. Use the pull bar for the final rows, then face-nail them, because the nailer will not fit against the last wall.
8. Finish the edges. Fit transitions at doorways (see our guide to hardwood floor transitions between rooms), then reinstall baseboard and shoe molding. Fix the shoe to the baseboard, not down into the floor, so the floor can move.

How Glue-Down and Floating Installs Differ

Glue-down

The layout and stagger rules stay the same. What changes is the prep and the adhesive. NWFA requires a flatter surface than nail-down, and it describes full-spread troweling, parallel stripes about 6 to 8 inches apart, and ends-and-grooves patterns, depending on the adhesive and flooring maker. Use the trowel and adhesive your flooring maker names, because the open time and the notch size are product-specific. If you ever need to undo a glued floor, see our guide to removing glued wood flooring from a subfloor.

Floating

Boards lock to each other and sit on an underlayment. The underlayment needs enough compression resistance for the flooring above it, and over concrete it may need a built-in vapor retarder; both are the flooring maker’s call. Floating is the usual route over tile as well, and our guide on floating a wood floor over tile covers that case. For underlayment choices, see our laminate flooring underlay guide.

The Expansion Gap Is Not 3/8 Inch

Many guides tell you to leave 3/8 inch at the walls regardless of the floor. NWFA’s guidance is different: unless the flooring maker says otherwise, the expansion space at walls and other vertical obstructions generally equals the thickness of the material. A 3/4-inch solid floor gets 3/4 inch, and a 1/2-inch engineered floor gets 1/2 inch. A gap that is too small leaves a swelling floor nowhere to go.

Wide floors may need room inside the floor too. NWFA notes that on spans wider than 20 feet, spacing between rows may be needed, and it shows how to estimate it: multiply the species’ dimensional change coefficient by the board width and by the expected change in moisture content. Its example uses red oak (coefficient 0.00369): a 5-inch plank that changes 4 percent in moisture content can swell or shrink about 0.0738 inch, so ten such boards side by side could move roughly 0.7 inch in total (our arithmetic from NWFA’s figure).

Mistakes That Cause Callbacks

• Skipping the moisture test and trusting that the room feels dry.
• Using the same fixed 3/8 inch gap for every floor thickness.
• Aligning end joints in a stair-step or equal-offset pattern, which NWFA says to avoid.
• Face-nailing the shoe molding into the floor so the floor cannot move.
• Nailing into particleboard, which NWFA excludes as a nail-down subfloor.
• Running boards parallel to joists with no second subfloor layer or bracing.

Finishing, Stains and Cost

Prefinished boards need no sanding after install. Unfinished boards are sanded and sealed after install; our guide to applying Minwax Polycrylic covers one finish option. If the floor ever gets water marks, see removing water stains from a wood floor. For a bamboo floor, the process is similar but the product rules differ, so read how to install bamboo flooring. To budget the job, our hardwood flooring prices guide has current price ranges.

Frequently Asked Questions

What is the correct expansion gap for wood flooring?

NWFA says the expansion space at walls and vertical obstructions generally equals the thickness of the flooring, unless the manufacturer directs otherwise. That is 3/4 inch for 3/4-inch solid flooring and 1/2 inch for 1/2-inch material.

Can you install solid hardwood over concrete?

Not by nailing, because concrete cannot hold the fasteners. Solid flooring can be glued down on concrete once the slab is tested, and NWFA flags a calcium chloride reading over 3 lbs per 1,000 sq ft per 24 hours or an in-situ RH over 80 percent as needing more drying or a Class I vapor retarder first. Engineered wood is the easier choice over a slab.

How far apart should flooring nails be?

For 3/4-inch solid and engineered wood 5/8 inch or thicker, NWFA’s standard schedule is every 6 to 8 inches along the board and 1 to 3 inches from each end joint, with at least 2 fasteners per board. Thinner engineered boards use 3 to 4 inches. Check the flooring maker, whose schedule takes priority.

How much should end joints be staggered?

NWFA recommends row-to-row end-joint staggering of at least twice the board width, which is 6 inches for 3-inch boards. Avoid stair-step patterns and equal offsets on consecutive rows.

Can you install wood flooring over carpet?

No. Carpet and its pad compress and hold moisture, and wood flooring needs a flat, firm, dry subfloor. Remove the carpet, tack strips and staples, then check the subfloor under it against the flatness and moisture figures above.