Stair Stringers

Old 10-04-00, 08:13 AM
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I'm building a 12' wide X 14' long treated deck on a friends house. Is their a formula to use to figure out the rise and run of the stairs and how many steps will be needed? I looked at several decks in the same neighborhood to see how they did it. I found that the rise was a consistent 7" tall (minus an 1 1/2" for the step)but the steps vary in number and width to get you to the ground. I'm installing the ledger board this evening so I don't know the exact height of the deck from the ground yet, but can someone please tell me the easiest way to figure stairs? The deck will be constructed of 2 x10 treated lumber and I was told to cut my stringers from 2 x 12 treated boards and then use 2 x12 boards for the actual steps. I've helped build several decks in the past, I know what code is in our area (7" rise) and I feel comfortable doing the rest of the deck, I just never had to do the actual figuring for the stairs. Any advice or help someone could give would be appreciated greatly. Thank you in advance. P.S. This is the first time I have used this sight and the information shared is incredable. Keep up the great work.
Old 10-04-00, 08:16 PM
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I posted quite a dissertation on this topic a long time ago.

Here it is (don't anyone give me a hard time about cutting and pasting! ya here?):

Building steps or stairs can be a real charge or a real challenge. Usually they are not too much of a challenge.

As a rule of thumb. . .the sum of the height of a riser and the depth of a tread should equal between 17" and 18". Best riser height is between 7" and 8". The sum of two risers and one tread should be between 24" and 25".

The width of the tread should be at least 36". Wider is better. 3'2" to 3'4" is preferred, but an outside deck stair is best built to suit you and look like it was intended that way.

The stringers for the stair should be made from 2x12. The treads could be either 2x10 or 2x12, and the risers can be 2x6, 2x8, 1x6, or 1x8. All should be CCA.

CCA is the wood preservative most commonly used. It is a copper, chromium, and arsenate mixture.

Find the the total rise (vertical distance) and divide it by the intended riser height. Start with the 7. This is your number of risers. Disregard the fraction. To get the individual (unit) rise, divide the total rise by the number of risers. This is the height of each riser.

Using the 17" to 18" rule subtract the riser height and the remainder is your recommended tread depth.

You could predetermine where you want the steps to end and divide the number of risers into that number to calculate the tread depth.

Use a framing square and "step off" the riser and tread height on a stringer. Repeat the stepping off process. Count the correct number of steps to be cut before you cut the board to length. It is better to have an extra than to be too short.

If necessary, rip the treads to their respective widths and cut them to their approx. 3 foot lengths (if that's what you choose). You might need to cut at least 3 full stringers to eliminate any possibility of sag in your stair treads.

When you assemble the parts the riser boards go on before the treads. On an outside stair, riser boards are optional and not necessary. Then attach the treads. Keep in mind that you can cut the tread depths wider if you want overlap (nosing).

Attaching the stringers to the deck has many variables. Your choice on methods and techniques. Your stair should have a handrail and probably spindles. The pattern should match the existing deck.

This is not as confusing or demanding as it may read, but if you are unsure of your capabilities don't hesitate calling a full-time carpenter. He should be happy to help you out. Some of them may not want to tackle a small job though. (of course, I would do it!)

Any questions can be redirected to me here in this forum or at my website below. Hope this all helps.

More than a Carpenter: Home repair & construction

Old 10-05-00, 06:40 AM
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Hi All,

You have addressed most of MY concerns regarding the construction of stairs however, the one point I did not quite understand is how to calculate the overall length of the stringer required to span a certain distance or height from the ground. Are all stairs set at a 45 degree angle making this computation simple?
Old 10-05-00, 06:22 PM
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You must step off the stair to get this length.

Stairs at a 45 degree angle would be too steep, 100% grade.

More than a Carpenter

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