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Stair Riser (6)

A stair "riser" is the vertical element of a set of stairs. Typically, the riser is a 1x8 board nailed to the stringers. However, sometimes there is no board at all - the risers are "open".

When you're building a set of stairs, one the the more difficult questions to answer is, "How many steps do I need and what size should the treads and risers be?" For most deck builders, this isn't as difficult of a question as it first appears. The reason for this is that most deck stairs go from the deck to the ground. Because of this, it usually doesn't matter how far the stairs extend away from the deck - the "run" of the steps can be whatever is easiest.

In practice, this means that deck builders only need to focus on making sure their risers are the within an acceptable range and then letting the stairs extend out as far as needed to be at a comfortable angle. Many codes require risers to be between 5" and 7.75" in height. The UBC dictates a riser range between 4" and 7" (make sure to check what your local codes require). Using a standard 10" for the horizontal stair run distance, the task is to select a riser height that will produce steps at a comfortable angle that are also within your code range.

There are rules of thumb that we can use to help us figure out a good riser height for our 10" run width. These rules help ensure that the stairs end up at a comfortable angle - not too steep and not too shallow. One rule says that two rises plus one run should be between 24” and 25”. So for our 10" run, a stair rise of between 7" and 7.5" would work great. If you don't like to use fuzzy rules of thumb, check out the stair rise/run table.

To figure out what the exact riser height should be, we divide the distance from the top of the deck to the ground. Whatever number we choose for our riser must divide evenly into that total height measurement. For example, if the distance from deck to the ground was 37", we would choose a riser height of 7-3/8" because it divides evenly into 37" five times - well close enough.

To figure this out, just keep dividing 37 by "whole" numbers until you get an answer that is seven and a little more (whole numbers don't have fractions - 1, 2, 3...). When dividing 37 by 5, we get an answer of 7.4. This tells us that we need 5 risers each 7-3/8" tall - you can use the Feet-Inch Calculator to convert any decimal number to an equivalent fractional length. To learn all about code requirements for stairs and how to build them step-by-step, check out the section on Stairs and Railings.