Attach Stair Stringers: Tips and Mistakes to Avoid

wood staircase

Stair stringers are the boards in a staircase that actually hold the stairs in place. The stair stringers are installed to run the length of the staircase. Some things to consider during planning include the size of the stair stringer, layout, and installation. Here are some mistakes to avoid and tips that will be helpful for you when attaching stair stringers.

1. The Size of Your Stair Stringers

Choosing what size your stair stringer should be is an important consideration when installing them. You should choose a board for your stair stringer that is no smaller than 2 by 10 inches. This piece should be comprised of solid wood as oppose to a composite material that is less expensive. You want to leave a yield of 3 1/2 inches of solid wood from the cut out when making the stair stringers. This will give you the strength to support several hundred pounds of weight.

2. Attach a Vertical Post for Support

One way to support additional weight on the stairs is to add a vertical post to the stair stringer. A vertical post or two placed beneath the stair stringer will provide additional support that is needed for the stairs. Depending on the location of the stairs, you may also want to attach the stringer to a wall with nails.

Use a minimum 2 by 12 inch stringer if it is not possible to either nail it to the wall or install a vertical post beneath it.

3. Lay out the Stair Stringer


There is a lot of precision that goes into laying out the stair stringer. For example, if you have a staircase that has 12 rises on the stringer, if you make a mistake in the layout that is as much as 1/16th of an inch, this will result in the stair being off by 3/4ths of an inch (1/16 inch times 12 = 12/16-inch = 3/4-inch).

When you are laying out the stair stringer, use a framing square. Your framing square consists of two sides, one that is 2 inches by 24 inches, which is the body, and the other that is 1 1/2-inch by 16 inches, which is the tongue. Hold the framing square by the shorter side or tongue and mark the run and rise of the stair stringer (elevation) using the markings on the body. It is best to practice using the framing square to make sure that the markings line up precisely. If you have problems using the framing square properly, go to a home improvement center for advice.

4. Proper Installation of the Stair Stringer

When installing the stair stringer always measure from the top of the floor down. Be sure to add an allowance for the thickness of the stair thread itself, about one inch.