The shorter riser adds almost 18' to the length of the stair. Now consider what you like in a stair and how much room there is in the plan. 1' would give you either an 11' or an 11.5' total tread surface both of which are generous. If the minimum tread is 9', you can ignore it but if it is 10' then the two possible designs are R=7.64'/T=10' and R=7.13/T=10.5'. Now consider the code (the limitations vary by state so don't make assumptions, read the code!). Using the Tread formula for the larger riser option the best tread would be 9.8' and for the smaller riser option the best tread would be 10.5'. The best formulas for determining the best riser to tread ratio are T=20-(4R/3) and R=15-(3T/4).

Getting too far from the established ratios makes you feel like you must lean more forward or backward (ie, rising too slowly or too quickly) as you climb. However, there are no other options unless you change the upper floor height so now determine the tread options for these 2 riser heights.įor comfortable climbing as the riser gets larger the tread should get smaller. Both are just fine but to me one is a bit too high and one is a bit too low. For an 8-11 floor to floor height 14 risers will give you a riser height of 7.64' and 15 risers will give you a riser height of 7.13'. Start with the possible riser dimensions since there will usually only be one or two. The nosing is added to the tread AFTER all the dimensions of the stair have been determined.įor me the ideal residential stair is R=7.5' and T=10' but that is not the place to start. Forget the nosing dimension it is not part of the tread dimension for design purposes.

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