Wood-framed floors at a first or second floor are designed to support people, furniture and appliances. In many older houses where subfloors were nailed instead of installed with wood screws and construction adhesive, the nails can loosen over time. As a result, certain types of movement may cause the floor to vibrate. In some cases, running a washing machine or walking across a floor that has a loose subfloor may cause vibrations. A capable do-it-yourself enthusiast can reduce floor vibrations by fixing the suspect areas.
Determine the area of a room where the floor needs to be fixed. Do this by hopping up and down and listening for the floor to vibrate. Another method is placing a glass of water on a table and walking or hopping on the floor. Measure from one or more walls and note the measurements to the area that vibrates most. Skip this step if a floor vibrates in a laundry room.
Access the underfloor area where the floor will be fixed. Use the crawl space opening to access below a first floor, or a stepladder to access the ceiling that's below a second floor. Refer to your measurements and mark the exposed floor joist or ceiling at the loose area. For a plaster or drywall ceiling, locate a joist with a stud finder and mark the location of the joist and two adjacent joists each side of that joist. Proceed to the next step for a plaster or drywall ceiling.
Put on safety glasses and a dust mask. Cut out sections large enough to install support blocks between the joists. If the joists are 16 inches apart, cut out 12-inch wide sections between the joists. For best results, stagger the sections 24 inches. Where a larger area of subfloor is loose, cut out additional sections, as necessary, to fix the entire area.
Measure the distance between the floor joists where 3-by-6-inch blocks will be installed. For exposed joists under a first floor, blocks should be installed between two joists each way of the marked joist. Additional blocks are installed when a larger area is fixed. Cut the blocks from pieces of 2-by-6 framing lumber with a circular saw or handsaw.
Blocking, Connectors and Adhesive
Measure the distance between the floor joists for 2-by-6-inch wood blocks. For exposed joists under a first floor, blocks install between two joists each way of the marked joist. Additional blocks are installed when a larger area is fixed. Cut the blocks from pieces of 2-by-6 framing lumber with a circular saw or handsaw.
Place each block flat with one of the 6-inch-wide sides facing up. Position 2-by-3-inch 90-degree framing connectors on the face of the blocks at each end. The outside corners of the connectors should align with the ends of the blocks. One of the 4-inch sides should extend upward from the face of the blocks for attachment at the side of a joist. Drive 1 1/4-inch joist-hanger nails at each of the machined holes at the opposite sides of the connectors and into the face of the blocks with a hammer.
Install the blocks between the joists one at a time. Apply a generous amount of construction adhesive along one of the 2-inch-wide edges of a block that is the upper edge that contacts the underside of the subfloor. Position the block between two joists and drive the lower edge upward with the hammer so the upper edge with the adhesive is tight against the underside of the subfloor. Attach each end of a block to the corresponding sides of floor joists with hanger nails at each of the machined holes in the 90-degree connectors.
Things You Will Need
- Measuring tape
- Stud finder
- Marking crayon
- Safety glasses and dust mask
- Reciprocating saw or drywall saw
- 2-by-6-inch framing lumber
- Circular saw or handsaw
- 2-by-3-inch, 90-degree framing connectors
- 1 1/4-inch joist hanger nails
- Construction adhesive
- For bigger joists, such as 2-by-10 and 2-by-12-inch, use two framing connectors at the end of each block.
- Moving heavy pieces of furniture to another part of a room may stabilize a floor and eliminate vibrations.
- Special rubber cups that fit onto the legs of a washer and dryer may reduce floor vibrations in a laundry room and adjoining rooms.
- Any sections of floor joists or wood subfloor that are rotted must be removed and replaced. Enlist a licensed contractor to perform the work.
- Always wear eye protection when working with power tools.
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