How to Build a Subfloor in a Basement

Placing a wood subfloor in a basement raises the surface of the floor enough to allow airflow and reduce the risk of moisture damage. A good-quality subfloor consisting of joists and plywood floor panels will easily support most floor finishes including tile, hardwood and carpet. Once a subfloor is in place, a basement becomes noticeably warmer and appears more like a consistent part of the house. Materials and tools for this project are available at most home improvement and hardware stores.

Things You'll Need

• Broom
• Patching compound
• Trowel
• Felt paper
• Tape measure
• 2-by-6 boards
• 2-inch twisted framing nails
• Joist hangers
• Hammer
• 1-inch framing nails
• Circular saw
• Plywood panels

Instructions

1. Examine the concrete basement floor for any defects, damage or other imperfections. Sweep the floor to remove any debris and dust. Fill both large and hairline cracks with patching compound and a trowel. Place rows of felt paper over the floor, with approximately 2 inches overlapping.

2. Measure the room and begin building a frame with 2-by-6 boards around the entire perimeter of the room. Connect the frame using 2-inch twisted framing nails; get the pieces tight against the walls. Measure along the longest walls, and make marks from the edge every 18 inches. Attach joist hangers centered over the 18-inch marks using 1-inch framing nails.

3. Determine the distance from one joist hanger across the room to the other hanger. Use a circular saw to cut 2-by-6 joist boards to fit the span and place them into each set of joist hangers. Hammer nails through the side of the hanger and into the side of the joist to secure them.

4. Place sheets of plywood over the floor joists, and cut them to size so that the edge lays over half of the joist to support the end. Hammer 2-inch nails into the joists through the plywood boards. Lay the next several boards in the same manner to create tight seams, and hammer nails into them and through the joists as well. Place one nail every 8 inches to get the best connection.

5. Walk the new floor and check for any loose areas or sections that seem uneven. Place more nails into the subfloor as necessary to get it tight and firmly connected.

Tips & Warnings

• Have an assistant help with placement and lifting of boards.

• Use proper precautions and wear safety glasses when working with power saws.

References

• “Remodeling A Basement, Revised Edition”; Roger German; 2010
• “Black & Decker Complete Guide to Finishing Basements”; Philip Schmidt; 2009