How to Build Stair Stringers

The construction of the simplest type of staircase develops from two pieces of wood that slope between one floor and another. These two pieces of wood are known as stringers and the steps (horizontal treads) and risers (vertical faces) are fitted onto them.

There are two basic ways of constructing a staircase with stringers - ‘open-string’ and ‘closed-string’. If a closed string staircase is used at least one side of the staircase is secured to a wall. This article will help you through the process of how to build stair stringers, regardless of which type of stringer you require and presumes you’re building your staircase out of wood.

Choosing the Wood

The choice of wood for the stringer is integral to the strength of the staircase and so selecting a good quality piece of wood is essential. Most staircases in homes are built with 2x10 or 2x12 lengths of wood.

If, when constructed, you’re not painting the staircase you may well already know the wood type you’re going to use. Otherwise any of the wood types commonly used in construction work are fine - so long as it doesn’t have any large knot holes in it and it isn’t badly warped!

Staircase Strength

The integrity of your staircase ultimately depends on two things. If it’s a closed-string staircase - how well it’s fixed to the wall at the upper floor, or if it has an open-string aspect to it; how well it is fixed to and supported by the legs it stands on.

Secondly, your choice of whether to use 2x10 or 2x12 for the stringers will affect the strength of the staircase. In this respect the depth of riser that you cut becomes important.

You should allow for at least 3 1/2” remaining in the stringer after each riser has been cut. Any less than that and the integrity of your staircase could be compromised by any substantially overweight visitors using it. Quite frankly, when as a nation we seem to be for ever expanding our waistlines, the choice of 2x12 stringers might not be a bad idea.

Tread and Riser Depth

Whilst the width of the steps is not important when determining the length of wood required for the stringers it is worth noting that a step tread depth of not less than 12” is recommended. If you’re building a particularly wide staircase, you might need stringers in between the outer ones to give it more strength.

In building your own staircase you can decide what riser height to have. However, a common height measurement for a riser is 8”. The one thing you do want to make sure of is that each riser is the same height.

What Length Stringer Do you Need?

You now need to do a bit of math. First get a measurement for the total rise height, or the vertical distance, that the staircase will cover (this must be between two level points). Divide the total rise by 8, to see how many steps you’ll have on the staircase. (Remember, this is based on 8” risers - but you can ultimately decide what value to use.)

What ever answer you get, round it up to the next whole number. To find the exact value for your step riser measurement; divide the total rise measurement by the whole number you’ve just arrived at.

Next, decide how deep you want the tread of each step to be, 12” is recommended; then multiply that value by the number of steps that you’ve just calculated. This new value is called the total run measurement.

To get the length of wood required for the stringer find the ‘square’ of the total rise and the ‘square’ of the total run measurements and add them together. The ‘square root’ of that answer is the length of stringer you require. Then when the stringers on-site, you can measure up and start cutting the ‘riser’ and ‘tread’ patterns using a carpenters square for accuracy.