You’re playing croquet in the backyard when you notice smoke pouring out of the barbecue grill on your elevated deck. You race around the house, in the front door, up the stairs, through the kitchen and out onto the deck, but it’s too late. Your steaks are charred.
 
There’s a lesson in this mishap, and it’s not that you must stay tethered to the grill while barbecuing or that you need to run more wind sprints. Don’t blame yourself; blame your deck. If it had steps down to the backyard, you probably could’ve saved dinner.

Adding steps to an elevated deck gives you, your family and your pets easy access to the yard and increases the space in which you can entertain, making the yard an extension of the deck. In addition, it provides an easy escape route from your home in case of emergency. Designing and building stairs is not as complicated as you might think. The right formula (see “Doing the Math,” p. 58) makes it easy. Working with contractor Keith Christensen of Minnetonka, Minnesota, I learned that adding a stairway to an existing deck is a project you can complete in a weekend with basic carpentry tools.

Designing deck stairs
Before you begin designing stairs, determine whether you really want or are allowed to have them. If you live in a townhouse or condominium, check your building association’s restrictions and regulations. If security is a concern, you may want to avoid adding access to your deck.

Available space impacts design. Determine the actual space requirements of the stairs you are considering. If space is limited, or if you want to limit the distance the stairs extend into the yard, consider incorporating a landing or turn to make the stairs more compact. Don’t be intimidated — the construction methods used to add a landing are the same techniques we show in this straight-run example. The difference is that you will do everything twice, making two landings and two short stair runs.

The stairs should be at least 36 in. wide. If your stairs will be wider and you are using 1-1/2-in. treads, a third stringer in the center is recommended (and often required, depending on local codes). A good rule of thumb is to add a stringer for every 18 in. of stair width. Some codes require riser boards — the boards that run across the front of each step. Our local code did not require them, but we included them in the design because we liked the finished appearance they provided.

When designing railings, follow a few general rules. First, if the stairway is more than four risers high, it must have a railing on at least one side. Second, the total railing height should be at least 34 in. above the treads. And finally, the maximum gap between balusters is 4 in. You can buy prefabricated handrails or create a simple handrail by routing a groove along the length of a 2x6 with a 1/2-in. core-box bit. But check with your inspector first to make sure the railing meets the code standard for your area. Once you’ve completed the design, it’s time to prepare the site. Pour a footing (check local codes for requirements) with an anchor bolt embedded at the center of the future landing post location. Also pour a concrete pad where the stair run will end. The pad should be at least 12 in. wider than the stairs, at least 3 ft. long and 6 in. thick. To make the stairs match the existing deck, use the same building materials. If your deck is untreated, thoroughly clean it and either leave the new stairs untreated or apply an exterior finish to both the deck and the stairs. If the deck is stained, plan to clean and restain it when you stain the stairs to achieve a closer match. Rather than siding stain, use deck stain, which is intended to withstand foot traffic. Any initial difference in appearance between the deck and stairs will fade after one season of use.

Doing the math
The following equations will help you determine the stringer length, stair height and tread depth. The term “total rise” refers to the overall height of the stairway (from the point where the bottom step will be located straight up to the finished deck), and the term “total run” refers to the overall length of the stairway.
1. Measure the total rise in inches.
1. Divide the total rise by an estimated riser height of 7.25 in. to determine the number of risers. Then round this number up to the nearest whole number.
2. Divide the total rise by the number of risers to get the exact height of each riser. (This number should be at least 6-1/2 in. but no more than 8 in.)
3. Subtract the height of the riser from 17.25 to find the tread depth. You have about an inch of flexibility to make the tread a comfortable depth.
4. To find the total run, multiply the number of risers by the depth of one tread.

After you have done the calculations for your site, check your numbers with the following two equations to be sure your design fits typical exterior stairway standards.
1. Riser height x tread depth = 72 to 76 in.
1. (2 x riser) + run = 23 to 25 in. If any of the results do not work for your situation, go back to step two and add or subtract 1/2 in. from the estimated rise (7.25). — BH