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How are stairs figured out?

Cesar R

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Total rise (of staircase) finish floor elevation to finish floor elevation.


Total Run (of Staircase) plan view distance (available) from top step to first rise.


Ideal rise/run stair is 7.5"/10" +/- (residential single family) depends upon who you talk to. Maximum rise is typically 8" with a 9" run. Multi Family and commercial are generally less than the ideal run.


The idea is to divide the total rise by a whole number to get something close to the "Ideal" or target rise. The run is then determined by dividing the total run by the number of risers, (less one-1 rise if the top riser is the floor deck-instead of a full stairtread, a piece of nosing will be the top step). The run can also be determined by just multipling the number of risers times the ideal or target stair run, if space is not an issue.


This is a real simple explaination, there are a few other little hiccups on the way when actually constructing them-really depends upon the type of construction


Now if your looking for arched, winder or spiral stairways life gets a little more interesting, hehehe -sinister laugh-


Hope it helps a bit


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this will be in the building codes relevant to your area.


in the building code in my area, they give you a formula ->


2R + G =


where R is the riser dimension (vertical height from stair to stair)


and G is the going dimension (the horizontal distance from one nosing to the next) - nosing is the very front part of each stair)

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I am draughtsman and designer of stairs for a living.

All of the above are correct although I use British Standards to comply with.

The goings and rise varies between straight and spiral/helical stairs.


If you need any help with a layout just send us a plan or something.

Include a basic specification to.


It can be shape you like; straight, spiral, helical, dog-leg, horseshoe, you name it!



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Yup a little math,


7" into 120" = 17.14" risers, round it to 17. Divide 120 by 17 and you get 17.0588" technically that is more than the maximum allowed for none private stairs. So 18 risers yeilds 6.6666" of rise per step. Then use the ""2rise+1run formula should equal 24-25" "" to figure the run, given your available space.


It's really not too bad. The design aspect is pretty simple, constructing & installing stairs on site gets wierd from time to time. Pushing the maximum allowed rise is typically the culprit!



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  • 6 years later...

Is there a formula for working out helical stairs, I am currently working on a project where I have 4 sets of helical stairs to figure out. I have got as the stairs working in a straight line but just need to work the curve in there now.

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