How to Install Hardwood Flooring Over a Bumpy Subfloor

Wood flooring adds a classic look to any room.

Hardwood flooring adds a classic look to any room. To have a level and smooth floor surface the subfloor needs to be level. Often the first step to a hardwood flooring project is to create the level subfloor. While sanding the existing subfloor may remove some of the bumps and high spots more severe bumps in the floor commonly require adding a new subfloor over the existing floor. The project requires extensive carpentry skills and adequate equipment but falls within the abilities of most do-it-yourselfers.

Things You'll Need

• 4-foot carpenter's level
• Roofing felt and shingles
• 1/4-inch plywood
• Wood putty
• 2-inch screws

Instructions

1. Mark the high spots of the subfloor. Use a 4-foot carpenter's level to determine which are the highest spots or bumps on the floor. Place one end of the level on a high spot. Lift the other end until the bubble shows level. The distance the end of the level is off the floor is the amount the floor will need to be shimmed in that spot.

2. Fill in the low spots with roofing felt or asphalt shingles. Fill the entire low area with the fill material. Any hollow spots in the fill material results in a floor that will creak when walked on. Fill all low spots in the floor.

3. Place another layer of subfloor across the filled floor. Use 1/4 inch plywood. Fasten it in place using 2-inch screws at the corners for a temporary fit. Check the level of the floor with the carpenter's level before proceeding.

4. Fasten the new plywood subfloor in place permanently using 2-inch screws placed every 8 inches through the subflooring and into the floor joists below.

5. Fill the screw heads and any gaps in the seams between the plywood with wood putty. Sand the putty smooth.

6. Lay the hardwood floor per the manufacturer's instructions.

Tips & Warnings

• The fill in the low spots of the floor must completely fill the area and be solid when compressed by the subflooring. Any gaps or air spaces in the fill results in creaking floors.

References

• Hardwood Installer: Wood Subfloor Preperation