# Stair units and the rule of 18.

Discussion in 'General Advice' started by wemeck, May 3, 2003.

1. ### wemeckActive Member

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Try to keep the height and size of your trends consistent through-out the entire stair unit. Otherwise you make a nasty "Actor Trap." One old trick is the rule of 18. Always make sure the height and the trend width add up to 18". So you could have a step that is 9" tall and 9" wide.

2. ### Jo-JotheSoundDogActive Member

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I was always taught 8" rise 10" tread was the ideal but you must measure and do the math before hand. But you want to try to get as close to these numbers as possible. The problem I see with this rule of 18 is a 17" rise with a 1" tread should work according to that description.

3. ### wemeckActive Member

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The reciprocal of your example, 1" rise with a 17" tread is a known architectural effect. But in no way was I suggesting the complete and total abandonment of common sense when working with the "rule of 18." Like any axiom, it has its limitations. But you made one hell of actor trap with your example. Or possible a nice trophy stand.

4. ### shipSenior Team EmeritusPremium Member

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You might want to look at page 237 of the Backstage Handbook III.
There is a crucial table presented on it that explains what's going on with your very broad figure.

Remember that 17" or 18" golden rule, or the 2R=T=25 rule of thumb formula are goals for normal building purposes. With those golden rules, there are minimum standards set by the UBC about minimum and maximum tread and riser dimensions as well as info about ladders and ramps.

For stage use, you can do what you need to since it's temporary, and those using it will have been trained in it's potential danger. Just like acting on a raked stage. The more the slope, the more the danger. The more you avert from a 11" tread and a 7" rise, the more dangerous that is going to be for the person using the stair. About as dangerous as installing a half height or 1.1/2 height stair at the bottom or top with out a landing. It's best to use that golden rule and slightly modify your treads and risers to fit in your space.

That's given you are not contiously making use of averting from the 18" standard say to help the talent find their role in the set being off kilter visually and by engineering of it. Kind of like both raking and sloping your set ever so slightly. Or cutting 1/4" off the leg of a 3-legged stool. Such design things are not enough to be heavily noticed but they can be felt.

5. ### wemeckActive Member

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Thanks for tracking that down! I knew my old Prof, David McLain, got it from somewhere.

6. ### wemeckActive Member

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I was watching this old house and it was an episode were they went to peoples house and solved issues. Well in this episode they were modifing a small stair unit so the owner would not bump his head when using the stairs. The two items of ieterest:
Item 1.) The carpenter on the project mentioned that a 8" tread (depth) is the minimum, and the height and depth should add up to 17".
Item 2.) When he was marking the runners he basicly clamped a small piece of 1x4 to the carpenters square making a triangle. He then used the 1x4 as a fence against the 2x12 and then marked off all the notches for the treads. Guiding the square, rotated with the 90 degree angle perpendicular to the 1x4 cross piece, down the 2x12.

It was pretty cool. At the end of the show, Steve the host, made a special point to talk about the special use of the carpenters square.

7. ### CHScrewActive Member

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A funny story about this. There is a set of steps outside our school that are concrete. At the top of the steps there is a paves walk-way. One summer the repaved the walk-way and went right up to the edge of the top step. So, the top step was about 1/4 inch higher than all the rest.

I use to get my lunch and go sit near the top of the steps, Just waiting for people to trip over tat top setp. About 3-4 people triped EVERY DAY.

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