How to Install Hardwood Floor Over Subfloor

Subfloor Requirements for Hardwood Installation

Hardwood floors require a structurally sound, flat, dry subfloor. The most common subfloor materials are:

• Plywood - the preferred subfloor for hardwood. Minimum 3/4" thickness for nail-down installation.
• OSB (Oriented Strand Board) - acceptable but more susceptible to moisture damage than plywood. Use with caution in humid climates.
• Concrete - requires special treatment (see our guide on installing hardwood over concrete)

Step 1: Inspect and Prepare the Subfloor

1. Remove all existing flooring, staples, tack strips, and adhesive residue
2. Check every subfloor panel for squeaks - nail or screw down any loose areas before installing hardwood on top
3. Check for rot, water damage, or delamination - damaged panels must be replaced
4. Check flatness with a long straightedge - the subfloor must be flat within 3/16" over 10 feet. Sand down high spots and fill low spots with floor leveling compound

Step 2: Check Subfloor Moisture

Use a Digital Moisture Meter to check the subfloor moisture content. Plywood subfloors should read below 12%. The hardwood being installed should read within 2-4% of the subfloor reading. If the subfloor is significantly wetter than the hardwood, allow it to dry before proceeding - installing over a wet subfloor causes cupping and squeaking.

Step 3: Install Rosin Paper (Optional but Recommended)

Roll out 15 lb rosin paper or builder's felt over the subfloor before installing hardwood. This provides a slight moisture buffer, reduces squeaking, and helps the floor feel more solid underfoot. Overlap seams by 4 inches.

Step 4: Plan the Layout

1. Run hardwood perpendicular to the floor joists whenever possible - this provides the strongest installation
2. Snap a chalk line parallel to the longest wall as your starting reference
3. Check that the line is square to the room
4. Plan the layout to avoid very narrow strips at the far wall

Step 5: Install the First Row

1. Place floor spacers against the starting wall to maintain 3/4" expansion gap
2. Lay the first row groove-side to the wall
3. Face-nail close to the wall (covered by baseboard later)
4. Pre-drill to prevent splitting near board ends

Step 6: Nail Down Subsequent Rows

1. Use the 3PLUS Pneumatic Flooring Nailer to blind-nail through the tongue at 45 degrees
2. Nail every 6-8 inches along each board and within 2 inches of each end
3. Use the tapping block to close gaps between boards before nailing
4. Stagger end joints by at least 6 inches between adjacent rows
5. Maintain expansion gaps at all walls and fixed objects

Step 7: Complete the Installation

1. Rip the last row to width and use the pull bar to pull it tight
2. Face-nail the last row close to the wall
3. Remove all spacers
4. Install baseboards and shoe molding to cover expansion gaps
5. Install transition strips at doorways

Products Used in This Guide

• General Tools MMD4E Digital Moisture Meter - check subfloor and hardwood moisture
• 3PLUS 4-in-1 Pneumatic Flooring Nailer - blind-nail installation
• WORKPRO Flooring Installation Kit - tapping block, pull bar, mallet, spacers
• WORKPRO 40-Pack Floor Spacers - maintain expansion gaps
• Maxiroc Transition Strip - doorway transitions