Cutting Holes in the Floor for a Staircase

Avoid cutting through any beams or joists unless you are absolutely sure that they're not helping to support the house.

1. Lay out the location where your new staircase will go using a tape measure and a chalk line. Make the hole 3 inches larger in each dimension than you want the finished opening to be. Mark the corners of the hole with a pencil, then stretch and snap the chalk line between the corners, leaving a straight line marked in chalk.

2. Cut away the flooring and subflooring along the chalk lines.

3. Support the floor from underneath by placing 2-by-4 props from the floor pressed up against the ceiling on both sides of the hole that you cut.

4. Cut away any joists that are crossing your new opening using a circular saw.

5. Measure the length of the stairway opening, and cut two pieces of lumber that match the width of the existing joists and the length of the opening. For example, if the floor joists that you cut are 2-by-8s and the hole is 72 inches long, you need two 2-by-8s cut to 72 inches.

6. Install the two boards that you cut by fitting them into the opening and using 3-inch screws to screw them onto the exposed ends of the joists that you cut, thus creating a hole with sides that are formed by the boards rather than by cut joists and the openings between them.

7. Cut two more boards for the short ends of the opening, and install them between the ends of the first two boards that you screwed in, creating a framed rectangular opening in the floor.

8. Remove the supporting 2-by-4s from underneath.