Hardwood Floor Installation: Nail-Down, Floating, and Glue-Down Methods
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Hardwood floor installation uses one of three methods depending on the subfloor type, the flooring product, and the room's location in the house. Nail-down is the traditional method for solid hardwood over wood subfloors. Floating works for engineered hardwood over any subfloor type. Glue-down bonds engineered hardwood directly to concrete. Each method requires different tools and different preparation, but all three start with the same critical step: acclimation.
Acclimation
Wood flooring must acclimate to your home's humidity and temperature before installation. Stack the flooring in the room where it will be installed for a minimum of 3 days. Seven days is better, especially during seasonal transitions when indoor humidity is changing. Leave the bundles open or cut the plastic wrapping so air circulates around the planks on all sides.
The room should be at its normal living temperature and humidity during acclimation. Running the HVAC system is essential. Do not acclimate flooring in an unheated garage, a freshly drywalled room that has not dried, or any space that does not match the conditions the floor will live in permanently. If the house is new construction, all wet trades (drywall mud, paint, tile grout) should be finished and dried before you bring flooring inside.
Check the moisture content of both the flooring and the subfloor with a pin or pinless moisture meter. For solid hardwood over plywood, the moisture difference between the flooring and subfloor should be within 2 to 4 percentage points. A larger gap means the wood will move significantly after installation, causing gaps between boards in dry seasons and cupping or buckling in humid ones. A decent pinless moisture meter costs $40 to $80 and is worth every penny for this one measurement.
Subfloor Preparation
The subfloor must be flat, clean, dry, and structurally sound. Check for flatness with a 6-foot straightedge or a long level laid on its side. The floor should be flat within 3/16 inch over 6 feet. High spots can be sanded down with a belt sander or floor sander. Low spots can be filled with floor leveling compound, which is a self-leveling cementitious product that you pour and spread with a gauge rake.
For plywood subfloors: walk the entire floor slowly and mark any squeaky spots with painter's tape. Screw those areas down with 2-inch screws driven into the joists below. Use a stud finder to locate the joists if they are not visible from below. Squeaks under hardwood flooring are nearly impossible to fix after installation because you cannot access the subfloor without removing the hardwood.
For concrete subfloors: test for moisture using a calcium chloride test kit or a concrete moisture meter. Concrete must read below 3 pounds per 1,000 square feet per 24 hours (calcium chloride test) or below 75 percent relative humidity (in-situ probe test). High moisture readings require a moisture barrier - either a 6-mil polyethylene sheet for floating floors or an epoxy moisture barrier for glue-down installations. Skipping this step on a damp slab will ruin the flooring within a year.
Remove existing baseboards and set them aside for reinstallation. Number each piece on the back so it goes back in the same location. Undercut door casings with a jamb saw or oscillating multi-tool set to the thickness of the new floor plus underlayment. Rest a scrap piece of flooring (and underlayment if applicable) on the subfloor next to the casing and cut at that height. The flooring slides under the casing for a clean look without gap-filling or caulk.
Nail-Down Installation
Nail-down is the standard method for 3/4-inch solid hardwood over plywood or OSB subfloors above grade. You drive cleats or staples through the tongue of each board at a 45-degree angle using a pneumatic flooring nailer. The nailer sits on top of the board, engages the tongue edge, and fires when you strike the plunger with a rubber mallet. This method creates the most stable, solid-feeling floor.
Rent a pneumatic flooring nailer and mallet from a tool rental center. Models from Bostitch, DeWalt, and Freeman are commonly available. You will also need an air compressor if the nailer is pneumatic, or you can rent a manual (mallet-driven) flooring nailer that does not require compressed air. The first 2 to 3 rows must be face-nailed because the flooring nailer cannot operate close to the wall. Pre-drill holes to avoid splitting the tongue, and fill the nail holes with color-matched wood filler after installation.
Start along the longest, straightest wall. Snap a chalk line 3/4 inch from the wall - this gap is the expansion space, which will be hidden by baseboard. Lay the first row with the tongue facing the room and the groove against the wall. Face-nail this first row through the top of the board.
Work across the room, driving cleats through each tongue at 6 to 8 inch intervals. Rack the boards as you go - stagger end joints by at least 6 inches between adjacent rows. Avoid H-patterns where end joints align in every other row, which creates a visible and structurally weak pattern. Pull boards from multiple cartons to mix color and grain variation.
The last 2 to 3 rows also require face-nailing because the flooring nailer will not fit between the boards and the wall. A pry bar (or flooring pull bar) pulls the last row tight against the previous one while you face-nail. The expansion gap at this wall is also 3/4 inch.
Floating Installation
Floating floors are not attached to the subfloor. The planks lock together with a click-lock or tongue-and-groove system and the assembled floor sits on an underlayment pad. This method works for engineered hardwood over any subfloor type, including concrete, and is the most DIY-friendly installation method because it requires fewer specialized tools.
Install the underlayment first. For concrete, use a combination underlayment with a built-in moisture barrier - products from Floor Muffler and QuietWalk are widely available. For plywood, a standard foam underlayment (2mm to 3mm thick) provides cushion and sound dampening. Overlap the seams by 6 inches and tape them with the manufacturer's recommended tape.
Leave a 3/8-inch expansion gap along all walls, columns, doorframes, and any other fixed objects. Use plastic spacers, which are cheap and available at any flooring supply store. This gap is critical - a floating floor that is pinched between walls will buckle. The buckle may not appear for weeks or months, usually showing up when humidity rises in summer and the floor expands.
Angle the tongue of each new board into the groove of the previous row at about 20 degrees, then press down to click it into place. The end joints snap together by tapping the short end with a tapping block and mallet. Never strike the exposed edge of a board directly - you will crush the locking profile and the joint will not close properly.
Floating floors feel slightly different underfoot than nailed floors. There is a subtle hollow sound when walking that some people find objectionable, especially on concrete subfloors. A quality underlayment with a sound-rating of IIC 70 or higher reduces this effect significantly. Cork underlayment performs better than foam for sound reduction but costs more.
Glue-Down Installation
Glue-down installation bonds engineered hardwood directly to a concrete or plywood subfloor using a urethane flooring adhesive. This method produces the most solid feel on concrete because the floor is bonded directly to the slab with no air gap. It is also the thinnest installation profile, which matters when matching adjacent floor heights at doorways.
Spread adhesive with the recommended trowel size - typically a 1/4-inch by 3/8-inch V-notch or square-notch trowel. Work in sections of 2 to 3 rows at a time. The adhesive has an open time (the window before it skins over) of 30 to 60 minutes depending on temperature and humidity. Do not spread more adhesive than you can cover within that time.
Set each board into the adhesive and slide it tightly against the previous board. Use a tapping block for tight joints but do not slide boards excessively - this smears adhesive onto the board surface, which is difficult to remove after it cures. Wipe any adhesive squeeze-up from the board face immediately with the manufacturer's recommended solvent.
Glue-down floors cannot be walked on for 12 to 24 hours after installation while the adhesive cures. Plan your exit from the room accordingly - start at the far wall and work toward the door.
Finishing Touches
Reinstall baseboards to cover the expansion gap. If you plan to paint the baseboards, do it before installing them so you do not get paint on your new floor. Use a finish nailer to attach baseboards to the wall framing, not to the floor - the floor needs to move freely under the baseboard.
Install transition strips at doorways, where the hardwood meets other flooring types, and at any change in floor direction. T-molding bridges two floors of equal height. Reducers transition from a higher floor to a lower one. Stair nosing wraps the edge of a step. Each serves a specific purpose and most flooring manufacturers sell matching transition pieces.
Wait 24 hours before moving furniture back. Use felt pads on all furniture legs - chairs, tables, couches, bed frames, everything. Do not drag furniture across the new floor. Lift and place. Rolling office chairs need a chair mat or hard-rubber casters rated for hardwood. Standard plastic casters will scratch the finish within days.
Frequently Asked Questions
Can I Install Hardwood Floors in a Basement?
Solid hardwood should not be installed below grade because basement moisture levels cause excessive expansion and contraction. Engineered hardwood installed as a floating floor over a moisture barrier works in basements that are dry and climate-controlled. Test concrete moisture levels before committing. If the slab consistently reads above 75% relative humidity, even engineered hardwood is risky without professional moisture mitigation.
How Much Extra Flooring Should I Buy?
Buy 10 percent extra for a simple rectangular room. Buy 15 percent extra for rooms with angles, closets, hallways, or complex layouts. The extra material covers cutting waste at walls and doorways, mistakes during installation, and future repairs if a board gets damaged years from now. Store leftover planks flat in a climate-controlled space.
Engineered vs. Solid Hardwood - What Is the Practical Difference?
Solid hardwood is a single piece of wood, typically 3/4 inch thick. It can be sanded and refinished multiple times over its life - often 5 to 7 refinishing cycles for standard 3/4-inch boards. Engineered hardwood has a real wood veneer (1 to 6mm thick) over plywood or HDF layers. It handles humidity changes better than solid wood and works over concrete, but thin veneers (1 to 2mm) can only be refinished once or twice, and the thinnest veneers cannot be refinished at all. If longevity and refinishing matter, choose engineered with a veneer of at least 3mm.