DIY: Build Up a Sunken Room

Pry off all of the old molding or floor trim around the perimeter of the floor using a flat crowbar. Try to get it off without breaking it if possible. If it breaks, plan on replacing it. If the room is carpeted, remove all the carpeting.

Get down on your hands and knees. One side or wall of the floor will be sunken worse than any other side. You will be able to see how far the floor has sunk by examining the paint, wallboard, lathe or composite material that makes up the wall. There will be a visible line where the old molding came off that indicates the original floor height. Measure from the floor to the line. For an example, assume it is 5/8 inch.

Set the table saw at 5/8 inch and rip enough of the poplar to stretch end-to-end across the floor below the molding mark where the floor has sunk.

Set the table saw at 1/2 inch and rip the same amount of poplar pieces. Set the table saw and rip the same amount at 3/8 inch. Set the table saw and rip the same amount at 1/4 inch. Finish by ripping the same amount at 1/8 inch.

Place the 5/8-inch shims directly below the where the molding was removed. Place them end-to-end the length of the wall. Place the 1/2-inch shims parallel with the first row 16 inches apart. Place the 3/8-inch shims parallel 16 inches apart. Following the same pattern, place the other two rows to form a stair-step affect.

Nail the strips to the floor using a pin nailer. Shoot pin nails 12 inches apart down the length of all the shims.

Lay the 5/8-inch underlay down one sheet at a time perpendicular across the shims. Shoot one staple into each corner with staple gun using 1 1/2-inch staples. Run a heavy bead of construction adhesive underneath the edge of the underlay. Insert four small wedges under the edge of the underlay between the long shims. Let the adhesive hold them in place.

Place another piece of underlay in place butted up against the first piece. Run glue under the edge. Insert wedges between the shims. Continue placing and laying underlay in the same manner until you have covered the floor. You may have to cut some pieces on a table saw. Just run a light bead of construction adhesive to the floor under the intersecting edges when the underlay extends past the shims to the level part of the floor.

Shoot staples spaced 10 inches apart around the perimeter of each piece of underlay. Cut and install new molding on top of the new underlay.