Can I Use an Existing Wood Floor as a Subfloor?

Q: I am remodeling in a house that has old hardwood flooring. Can I leave the hardwood as a subfloor?

Brett Miller, the National Wood Flooring Association's VP of certification and education, answers:

Yes, you can install over an existing wood floor, provided it meets some important conditions. First, make sure doing so won't create problems with height differences at areas such as transitions with other rooms and stairs. Then, be sure the existing floor is flat, clean, dry, structurally sound, free of squeaks and free of protruding fasteners.

An existing floor used as a subfloor has the same flatness requirements as any other subfloor. Per the NWFA Installation Guidelines, those requirements are:

• for fasteners 11⁄2 inch and longer, the subfloor should be flat to within 1⁄4 inch in 10 feet or 3⁄16 inch in a 6-foot radius.

• for glue-down installations and fasteners less than 11⁄2 inch, the subfloor should be flat to within 3⁄16 inch in 10 feet or 1⁄8 inch in a 6-foot radius.

If the flooring is out of those tolerances, you will need to sand down high spots or fill in the low spots. If you are sanding, keep in mind that if the home was built prior to 1978, the EPA's Lead Renovation, Repair and Painting (RRP) Rule will apply.

You'll want to carefully inspect the existing flooring and repair, replace or re-fasten loose or damaged flooring, as any loose areas or voids will allow movement in the new floor, which causes squeaks.

Be sure to inspect the floor carefully for signs of moisture damage and do the same moisture testing as you would on any other job.

Once that existing wood flooring is ready to act as a subfloor, you will need to install your new floor at a 45-degree angle or perpendicular to the existing flooring. If you must install parallel to the existing floor, lay a minimum of 3⁄8-inch plywood over the top to increase stability.