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How to Lay Out Floor Joist

How to Lay Out Floor Joist. If you're building a house or adding on a room, you must lay out floor joists once the basement walls are up. Joists are supports upon which the subfloor is placed.

These run from the sill to the girder, which you place halfway between the outside walls and gives the ends of the joists a place to rest. It's important to lay out floor joists correctly.

  1. Measure the size of the area where you are laying out the floor joists to determine how many joists you need. Joists are generally 2 by 8 inch or 2 by 10 inch boards.

  2. Attach a header to the sill by standing a board on end so the wider part of the board is perpendicular to the sill. Toenail header to the sill.

  3. Cut joists by measuring from the header on one wall to the far edge of the girder. Repeat by measuring from the opposite wall to the other edge of the girder. Cut all joists.

  4. Starting at one end, measure 15 1/4 inches from the wall to the outside edge of the first joist. Mark with a pencil. Attach the first joist with a joist hanger nailed to the header or toenail joist end into the header.

  5. Lay out joists by measuring 16 inches on center from the first joist you installed. Repeat the process to install the joists on the opposite wall. Install by using joist hangers or toenailing into the header and the other end coming to rest on the girder.

  6. Nail joists together where they lay side by side on top of the girder. Toenail nails into the girder to hold the ends of the joists in place. Make a double joist where you can construct a wall atop those joists.

  7. Warning

    Always wear safety glasses or goggles when cutting wood.