How to Frame a Subfloor

The subfloor of the home is one of the most important structural elements of the building. The framing of the subfloor supports the entire weight of the house above it. Because it is so important, it is recommended that you use prefabricated joists that have been professionally engineered. Every locality has regulations concerning the placement and fastening techniques of residential floor joists. Standard protocol for the placement of these units is at 24-inch centers, but you should check with your local building inspector before you begin the project.

Treated boards, 2 inches by 8 inches by 16 feet
Circular saw
Pencil
Drill with 1/2-inch bit
Caulk gun with construction adhesive
100-foot tape measure
Engineered plans for your house (formerly known as blueprints)
Engineered, prefabricated joists
16d galvanized nails
Hammer
Plywood subflooring, 4 feet by 8 feet by 5/8 inch
1/2 inch galvanized wood screws, two
Screw gun
Work gloves
Safety glasses

Instructions

- 1
  Prepare your sill plates. Lay the boards out around the perimeter of your foundation. Cut the boards with your circular saw as necessary to make a perfect fit around the entire foundation.
- 2
  Stand each of your 2-inch by 8-inch boards on top of the block foundations. Mark the location of the metal studs in the foundation onto the wood with your pencil. Make a hole through the boards at each spot with the 1/2-inch bit on your drill.
- 3
  Apply three beads of construction adhesive onto each of the boards with your caulk gun. Place one bead down the center of each board and one bead on each side of the board. Keep the side beads one inch from the edge to prevent spillover. Lay the sill plates around the edges of the foundation, glue side down, with the metal studs protruding through the drilled holes in the wood.
- 4
  Stretch your 100-foot tape measure along each of these support sill plates. Look on the engineered plans for your house to learn which are the support walls. Make a pencil mark every 24 inches along each support wall sill plate. Place your engineered, prefabricated joists every 24 inches on the sill plates, using the pencil marks as a guide. Nail each joist in place by driving two of your 16d nails at an angle through each side of the joist to attach it to the plate below.
- 5
  Apply construction adhesive on top of each joist. Cover the entire floor with plywood subflooring. Drive screws through each piece of plywood with your screw gun. Place a screw every 6 inches along each joist to complete the subfloor.

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