How to cut stair stringers.

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Don't be intimidated by calculating straight stair stringers ever again. An internet acquaintance of mine, Quintin Shalla, has written an Excel spreadsheet that does most of the work for you. Stair stringer calculator.

Stair Codes 1.3 mb pdf file.

Stair stringer mounting
As an exercise, let's imagine you need to make a stair that is 74.79 inches high, and 104.04 inches long. These measurements are taken vertically floor to floor, and about where you want the stair to travel to horizontally. If you've decided to try to use nine steps, your rise will be 8.31 inches, and your run would be 11.56 inches. Before you commit to a specific number of steps, measure a stair you have access to and see what feels comfortable for you. The sizes you're making the cuts will often determine what dimension material you'll need to purchase for stringers. An old rule of thumb went something like "two runs and a rise equal 25 inches". I've found plus or minus a couple is close enough for me.
Stringer for stairs When you've decided on a size, clamp a straight stick to a steel square with C clamps at the sizes your run and rise will be. After tracing the square for the first run and rise, slide the square along the stringers edge for the next set. After all the steps are drawn you'll need to cut the bottoms off the stringers where they sit on the floor. This cut allows the stringer to drop down the thickness of your treads so the first step won't get higher when its tread is added.

If you're planning on attaching riser boards, they close off the fronts of the steps so you don't see under the steps, determine if you need to make the top most run longer to compensate for the riser boards thickness. The top riser board may or may not consume some of the top steps width depending on whether or not the stringer attach area is already faced or if you'll be adding a board there too.

Stringer measuring
There are at least three ways stair stringers are usually attached. The left most stringer example is to be avoided! As a side note, the two examples on the left also are calculated using one less rise than run as they both are mounted a rise and tread thickness down from the top surface of the decking.

I usually just use the square for the first stringer, then cut and trace it for the remaining stringers. This will guarantee the stringers are all the same length, which isn't always the case after sliding the square along so many times.

Stair stringer measuring This is perhaps the most dangerous way a stringer could be fastened. Notice how easily the stringer could split with so little bearing against something solid. This has been a very common way of building when a better way isn't known. I've often seen this done and cringe when I do knowing it's an accident waiting to happen
Stair stringer When the upper step can't be flush with the landing, the stringer should be built longer so it can pass behind the face board to a suitable mounting position. This method usually requires the face board to be notched to allow the stringer to pass through. This way of mounting a stringer does requires a longer stringer and somewhat weakens the face board, but is much preferred to the previous method.
Stringer cutting If you're planning to use this arrangement in attaching stringers, be aware that you'll also need to cut the stringers uppermost run a little longer where there is an interference with the face board. This doesn't usually weaken the stringer substantially, but be cautious as you're actually thinning the stringer slightly by cutting deeper through it. The run dimension will need to remain the same as the others even though the run passes through under the face board.
Stringer attachment By far the preferred method of attachment is as shown here in this example. The face board as well as the stringer are not cut any more than necessary. The only real drawback is the top stair tread being flush with the deck is causing the stair to be one tread longer in its total length. This way of cutting stringers actually has the same number of rises as it does runs. The other two stringer types have one less run than rise.

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