How to Build Sub Floors

Sub floors are set on the foundation of a structure. A sub floor provides the surface for whatever kind of finished floor you are installing (carpet, vinyl, hardwood or any other). For our example here, we're going to build a sub floor for a shed or storage building. Read on to learn more.

Difficulty: Moderate

Instructions

Header Joist

1. Determine approximately how much weight will be on your sub floor. For this example, we are using 2-by-8s to build sub floors. Our sub floor will be 10 by 10 feet.

2. Cut your header joist first. Your header joist is the outside joist that you attach your inner joist to. Cut two 10-feet lengths and two lengths that are 9 feet 9 inches.

3. Nail your 9 feet 9 inch pieces to the inside of your 10-feet pieces. This gives you a 10 by 10 feet box.

4. Square your four corners by measuring diagonally. Move one way or the other till both measurements are the same.

Inner Joist

5. Lay out your inner floor joist on 16-inch centers by hooking your tape measurement on one end of your header joist, pulling your tape to the other end. Set back 3/4 inch from your 16 inch centers.

6. Duplicate Step 1 on the other side of your header joist. Use a speed square to mark your lines on the inside where your inner joist will set when you build sub floors.

7. Cut your inner joist to 9 feet 9 inches. Now it's time to add your joist hangers. Joist hangers are made out of metal to support the weight on the floor joist. Nail them into place.

8. Slide your inner joist 2-by-8s in your joist hangers. Nail off with 16-penny nails.

9. Put caulking (plywood adhesive glue) on the top of the floor joists. This will keep the floor from squeaking and buckling.

10. Use 3/4 tongue-and-groove plywood. Stagger joints when building your sub floor. Nail down with 8-penny framing nails or screw down with 2 1/2 inch wood screws.