Building stairs is a key carpentry technique. This tutorial will show you how to build stairs and calculate stair stringers. (Stair building is also part 5 (of 7) steps in the 10x10 deck example).
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Designing and cutting your own stringers for your stairs will guarantee that each step(tread) is the exact height(riser) and depth(run) for your structure. If these terms are new to you, don't worry. By the time you finish reading this tutorial, you will have all of the knowledge you need in order to design and build a perfect set of stairs.
Use the stair section diagram below for reference.
The mathematical relationship between the rise and run of each step is very important in stair design. One generally accepted rule for calculating step rise and run is: the sum of two risers and one tread should be between 24 and 25 inches.
For example, if you have a step rise [F] of 7 1/4 inches, you could calculate your step tread [B] depth by using the following formula:
|Riser + Riser + Tread = 25|
|7.25 + 7.25 + 10.5 = 25|
As indicated above, the result is a tread depth [B] of 10.5 inches.
To calculate the number and sizes of risers and treads for a new set of stairs, first divide the total rise [A] by 7. For example: if the total rise [A] of a deck or landing is 36.25", the result is 5.17". Since the number of risers must be a whole number, pick the whole number closest to 5.17 (5 in this case) and divide it into the total rise:
|36.25" / 5 = 7.25"|
|Number of risers = 5|
|Riser Height: 7.25"|
The number of treads will always be one less than the number of risers. Previously, we calculated a tread depth [B] of 10.5" for a set of stairs with 7.25" risers [F]. Use the following formulas to calculate the total run:
|Number of treads: 4
Tread Depth = 10.5"
|Total run = 4 x 10.5"|
|Total run = 42"|
The above stair run will have 5 risers at 7.25", and 4 treads at 10.5", resulting in a total run of 42".
Note, that with this stair design, the last (top) riser is part of the landing or upper floor. It will not be included as part of the stair stringer.
Now that the number of treads (4) and tread depth (10.5 inches), and
the riser height (7.25 inches) of each step has been determined, we have
the information that we need to begin laying out the stringers.
You can also use the stair calculator to calculate the rise and run of each step, as well as some useful information related to stringer layout and building stairs.
A very important part of building stairs is the layout of the stringers. The stringers should be cut from 2 x 12 framing lumber, #2 grade or better quality, free of knots. The images below show how a framing square is used to lay out the stringers [C], and a how the first stringer is used as a pattern for the remaining stringers [D]. This is very important, because if you layout each stringer separately, not only does it take more time, but the second or third stringer may not match up to the first if there are any variances in the shape of the board. Using the first stringer as the pattern for all of the remaining stringers will eliminate this potential stair building problem.
|[C] 2x12 Stair Stringer Material||[D] Stringer Pattern|
|[E] Circular Saw - Use a circular saw to start the cut. Cut up to the layout marks, but not beyond.||[F] Jig Saw - use a jig saw (or hand saw) to finish each cut.|
|Here's a couple of pictures showing building stairs in action.|
|[H] View from the underside of a set of rough framed stairs.||[I] Side view of a set of rough framed stairs.|