Stair Design Basics

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Stair Design Basics

Make them graceful, but also make them safe

Posted on Aug 11 2017 by Martin Holladay
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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:

  • Safe stairs require a larger area than unsafe stairs; devoting more area to stairs conflicts with the green principle favoring smaller houses.
  • Safe stairs requires excellent lighting; this conflicts with the green principle favoring reduced energy use.

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:

  • Every open stair needs a guard (something along the sides to keep people from falling to the right or the left). If the guard has balusters, the spaces between the balusters shouldn’t be wider than 4 inches.
  • Every stair needs a graspable handrail (a round handrail with a diameter of about 1 1/2 inch). Note that a graspable handrail isn’t the same thing as the rail at the top of a guard. The height of a handrail should be 34 to 38 inches above the tread nosing.
  • Risers need to have a consistent height. It’s dangerous for the stair's top riser or bottom riser to have a different height from the other risers. Carpenters who cut and install stringers sometimes fail to consider all of the relevant details, which may include the thickness of the subfloor on both floors, the thickness of the finish flooring on both floors, the thickness of the rough treads (if any), and the thickness of the finish treads. Before you cut those beautiful knot-free 2x12s, spend plenty of time with a clean sheet of paper and a sharp pencil.
  • Changes in elevation that require one or two risers are dangerous. Either create a difference in elevation that requires a minimum of three risers, or bring up the flooring height of the lower room to the same elevation as the higher room.
  • Design and install good lighting for your stairs. With stairs, more illumination is always better than less. You can provide lighting from above, or use special wall-mounted stair lights near the treads. Don’t install sconces — they get in the way when you move furniture.
  • Aim for 7-11 stairs: that is, stairs with a riser height that is close to 7 inches and a tread depth that is close to 11 inches. Although this principle requires more area than code-minimum stairs with 7 3/4 inch risers and 10 inch treads, the result is safer stairs.

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 of 11 inches. Because this code change would require homes to devote more floor space to stairs, and therefore slightly increase the cost of new homes, the National Association of Home Builders (NAHBNational Association of Home Builders, which awards a Model Green Home Certification.) went ballistic. NAHB instituted a major lobbying effort to defeat the 7-11 stairs, and (unsurprisingly, since NAHB lobbyists have very deep pockets) NAHB won the battle.

[Photo credit: www.nycremodeler.com]

Opinions on this matter are strong, but here’s my take: 7-11 stairs are safer than steeper stairs, so builders should aim for the 7-11 ideal.

Wide stairs provide enough room for bookshelves

Building codes require residential stairs to be at least 36 inches wide (drywall to drywall); 42 inches is better.

If you are designing a two-story house for a book lover, consider building stairs that are 52 inches wide — wide enough to provide room for 10-inch deep bookshelves on one side of the stairs. If you make the stairs 62 inches wide, you’ll have room for 10-inch-deep bookshelves on both sides of the stairs.

Martin Holladay’s previous blog: “Ten Common Mistakes Made By New Home Builders.”


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Image Credits:

  1. Ferguson and Shamamian Architects - www.fergusonshamamian.com

1.
Aug 11, 2017 8:10 AM ET

Edited Aug 11, 2017 8:16 AM ET.

How to compute exact riser height and tread depth
by Robert Opaluch

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.
Aug 11, 2017 8:35 AM ET

Tread depth
by Reid Baldwin

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.
Aug 11, 2017 9:10 AM ET

Edited Aug 11, 2017 9:13 AM ET.

Tread depth
by Robert Opaluch

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.
Aug 11, 2017 10:26 AM ET

Treads
by Malcolm Taylor

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.
Aug 14, 2017 1:07 PM ET

Edited Aug 14, 2017 1:11 PM ET.

NAHB
by Gordon Franke

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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