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Musings of an Energy Nerd

Stair Design Basics

Make them graceful, but also make them safe

Could the design of these stairs be improved? Perhaps. Wider treads and shorter risers would probably improve the safety of the stairs, and the sconce at the top of the stairs makes furniture moving awkward. But the bookcase on the right side is a nice touch.
Image Credit: Ferguson and Shamamian Architects - www.fergusonshamamian.com

Stair design requires attention to all of the usual rules of residential design. Stairs should be graceful, useful, and comfortable. In addition, stairs must also be safe. Clearly, safety is more important for stair design than for most design issues (for example, ceiling height or window orientation).

Once you understand the basic principles of stair design, you’ll probably notice that lots of stairs lack a graspable handrail, or have inconsistent riser heights, or are dimly lit. Examples of flawed stairs are unfortunately common.

Why should green builders care?

Is stair design a green issue? Perhaps. There are at least two ways that stair safety principles are in mild conflict with green construction principles:

I don’t want to belabor these two points, because the conflicts are obviously minor. Safety clearly trumps building size targets or energy use targets.

Code requirements

There are lots of good online documents on code requirements for stairs; for example:

Stair safety basics

I won’t try to recreate these guides here. Instead, I’ll focus on the most common stair safety issues.

Designers and builders need to get these important details right:

The 7-11 controversy

Jake Pauls, a safety consultant from Silver Springs, Maryland, has carved out a niche as one of the nation’s most vociferous advocates for stair safety. He has been waging a tireless campaign is favor of the 7-11 stair for more than 30 years. Pauls argues that 7-11 stairs result in lower injury rates than steeper stairs.

Pauls (and other 7-11 advocates) won an early victory in 1991, when BOCA, one of the model code organizations that pre-dated the establishment of the International Code Council, voted for a code change establishing a maximum stair riser height of 7 inches and a minimum stair tread width…

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5 Comments

  1. User avater
    Robert Opaluch | | #1

    How to compute exact riser height and tread depth
    Agree that 7" should be the maximum riser height, and strive for closer to 6" for safety and ease of climbing stairs, especially for children and the elderly.

    I’d add something like the following, for those who can’t view the Fine Homebuilding “subscribers only” article:
    To compute the exact riser height and tread depth for your stairway:
    1. Measure the vertical distance between the finish floors (height floor to floor). Divide by 7”. That tells you the approximate number of steps up the stairway, which is the number of risers. (That number might be about 15.4 for 8 foot ceilings plus floor framing.) Round the number up or down, preferably up, to the nearest integer (no fractions or decimals for the number of risers).
    2. Divide the floor-to-floor height by the number of risers. That tells you the height of each riser. It should be about 7” (maximum 7 ¾” allowed). For a less steep stairway for the safety of children and ease of climbing stairs by the elderly, try to get riser height closer to 6”, by increasing the number of risers by 1.
    3. Once you have the riser height, compute a comfortable and safe tread depth for that riser height:
    • Tread depth equals 25" minus twice the riser height
    For a riser height of 7”, that gives you a tread depth of 11”
    For a riser height of 6.5”, that gives you a tread depth of 12”
    4. The treads must stick out beyond the risers about 1” (3/4” minimum to 1 ¼” maximum allowed), called “nosing”. Therefore your tread stock must be tread depth plus nosing, or 11” + 1” = 12” depth (or 12” + 1” = 13” depth). If you design the risers to rest on top of the treads and reach the bottom of the tread above it, the tread stock also must be increased by the thickness of the riser boards, typically another ¾”.
    5. Riser stock would be less than the rise described above, by subtracting the thickness of any tread stock above and below it. Useful to draw a diagram of the stair design.

  2. User avater
    Reid Baldwin | | #2

    Tread depth
    Robert,

    Item 3 above yields longer tread for a shorter rise. That intuitively seems backward to me. Is matching a typical stride more important than controlling the steepness?

  3. User avater
    Robert Opaluch | | #3

    Tread depth
    Reid,
    Yes the formulas for computing tread width will make a comfortable and safe stride up and down stairs for adults. There are a few different formulas but they all yield similar results. Less steep stairs have both shorter rise and longer run (tread). Steep stairs have longer rise and shorter run. Like a ladder has a steep rise but very short run, and outdoor stairs have more like a 6" rise and 12" run, so you can't tumble down slippery outdoor stairs like you would tumble down a steep interior stairway or ladder.

  4. Malcolm Taylor | | #4

    Treads
    One of the reasons tread width is often shorter than might be desirable is that the stock they are commonly made from (both lumber and pre-made OSB) is typically 11" to 11 1/2".

  5. Gordon Franke | | #5

    NAHB
    Just because the NAHB has "very deep pockets" doesn't mean they didn't have valid arguments against the 7-11 minimum. There is a lot more to such issues than "is it safer, if yes then make it mandatory."

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