"Gee, I wonder how my subfloor's holding up." No, it's probably not something you think about often. In fact, you may never consider your home's subfloor--until it begins squeaking or you have to replace the covering over it (see the Carpet Fix-It Guide, the Resilient Flooring Fix-It Guide, and the Wood Flooring Fix-It Guide). It just does its job day after day: supporting the flooring you walk on. Let's call a quick meeting of the Fix-It Club to take a look at the subfloor.

How Does It Work?

A subfloor is a floor laid on top of the floor joists, to which a finished, decorative floor is fastened. If your home's floor is of poured concrete, that's the subfloor. Plywood or planks also provide a solid platform to which tile, vinyl, hardwood, carpet, etc. can be fastened with nails or adhesives. To hold the finish flooring, the subfloor must be stable, relatively smooth, and waterproof.

What Can Go Wrong?

The most common problem with a wood subfloor is annoying squeaks when someone walks across the floor. Squeaks occur when pieces of wood rub together. Concrete subfloors don't have this problem, but they can become water damaged and crack.

How Can I Identify the Problem?

If a wood subfloor squeaks, first you must try to locate the squeak. If the floor joists can be seen from below the floor (as from a basement or crawl space), watch from below while someone walks across the floor above. You may spot movement between joists and subfloor, or loose bridging between joists. Mark the location with chalk or another marker so you can find it again when you've gathered the needed tools and materials.

If you can get at the squeak from below through a basement or crawlspace, you can repair it with an angle iron, screws, a cleat, or a shim (see below).

Fix-It Tip

Wish you could lubricate a squeaky floor? Maybe you can! Wood flooring can be "lubricated" with talcum powder. Spread the powder over the boards in the problem area and work it in between the boards using your hand or a small brush. Then walk around the area to work the powder in. Repeat a few times and you may remove the squeak--without having to drive a nail.

If the squeaky subfloor is below a wood floor and there is no access to the subfloor from below, you can refasten the loose section of subfloor to the nearest joist through the finish floor (see below).

If the squeaky subfloor is beneath tile, vinyl, or carpet and there is no access from below, you can try to reset the loose boards from above (see below).

If the subfloor is concrete and shows damage, you will need to remove the flooring material and use a concrete patch product (available at hardware stores) to fix it, following the manufacturer's instructions (see the Concrete Fix-It Guide).

What Parts, Materials, and Tools Do I Need?

Replacement parts are available at building material retailers, hardware stores, and home centers. The tools you will need to fix a damaged subfloor include these:

• Hammer
• Screwdrivers
• Drill
• Angle iron
• Screws
• Nails and washers
• Cleats and wood blocks

You can fasten loose subflooring from underneath using screws.

What Are the Steps to Fixing It?

Repair a squeaky floor from below with an angle iron:

1. Find and mark the location of the squeak from below the subfloor.
2. Install an angle iron on the joist so the top of it is about 1/4 inch below the top of the joist.
3. Firmly screw the angle iron into the subfloor to pull it down onto the joist.

Caution!

Make sure that the screws installed in the subfloor from below are not longer than the subfloor and flooring is thick or they will come up through the flooring!

Repair a squeaky floor from below using screws:

1. Drill holes through the subfloor slightly smaller than the screw threads.
2. Install washers and wood screws 1/4 inch shorter than the total floor thickness.

Repair a squeaky floor from below using a cleat:

1. Mount a cleat against a joist under the loose boards.
2. Prop and tap so the cleat is snug against the subfloor.
3. Nail to the joist.

Repair a squeaky floor from above (wood floors):

1. Use a stud finder to locate the joist.
2. Drill pairs of pilot holes angled toward each other
3. Drive 3-inch ring-shank nails or screws through the flooring, the subfloor, and into joist.
4. Set the nailheads or countersink the screws, and cover them with wood putty that matches the color of the boards.

Repair a squeaky floor from above (not recommended for ceramic or other hard tile that may break):

1. Locate and mark the location of the squeak.
2. Using a hammer and a block of scrap wood as a buffer, pound the floor firmly over the squeaky boards in the area around the squeak to force loose nails back into place.