A deck’s stairway should be planned for carefully, so that all the rises (the vertical height of the steps) and all the runs (the horizontal length of the treads) are equal. If the bottom or top step is noticeably different in height or length from the other stairs, it will be a tripping hazard. Also, the stairs and its railing must comply with codes, which are designed to keep it firm and safe. Using prebuilt stairs will usually not meet code.
First, learn the parts: A landing pad is a flat surface made of concrete, pavers, or gravel at the bottom of the steps. If a stairway will not be used often and the lawn is flat, a landing pad can sometimes be omitted. Treads are the horizontal boards that you step on. Treads may be made of a single 2x12 or 2x10, but are often made of two decking boards or 2x6s. A stringer is a wide board, usually a 2x12, that runs at an angle from the landing pad to the deck framing and supports the treads. An “open” stringer has notches that you can see; a “closed” stringer is a solid board with cleats for the treads, or an open stringer with a solid board attached to the side. Risers are boards installed on end to cover the vertical spaces between the treads. Risers are often made of 1-by material, fascia board, or decking.
A unit run is the width (or depth) of a single tread. A unit rise is the vertical distance from the top of one tread to the top of the next tread. The total run is the overall horizontal distance traveled by the stringer. The total rise is a stairway’s overall change in height, from the landing pad to the top of the deck’s decking.
Now, some common code requirements, along with our recommendations:
- The stair’s treads should be at least 36 inches wide. We think stairs should be at least 48 inches wide, so they don’t feel cramped.
- The maximum allowable unit rise is 7 3/4 inches, and the minimum unit rise is 4 inches. For recommendations on rise-run combos, see the tip.
- The difference between a stair’s longest and shortest riser height or stair depth should be no more than 3/8 inch. This is pretty strict, so take the time to plan your stringers carefully.
- An open stringer should have notches that are not too deep, or the stringer will be weak. See the illustration [place tk] for the required minimum dimensions of the uncut portion of the stringer.
- The stair’s railing posts (near the bottom of the stairs) should be firmly attached. Anchoring to the side of a stringer may be enough, but many inspectors prefer that the posts also be sunk in concrete footings, for extra rigidity.
- The stair railing should include a graspable handrail.
- Openings in the railing should be no larger than 4 3/8 inches between balusters, and 6 inches between the bottom rail and the tread, as seen in the illustration.
- Stringers should be spaced close enough to adequately support the treads. This spacing depends on the tread materials. If treads are 2-by lumber, stringers can usually be as far apart as 16 inches on center. If 5/4 decking or composite decking is used, they should be 12 inches or closer. Be sure to check with your building department.
[tip] Comfortable Rise-Run Combinations
For comfortable stepping, a general rule of thumb is: the added total of the rise and run should equal between 17 and 20 inches. That means that the lower the rise, the longer should be the run. Two examples: A rise of 7 1/2 inches plus a run of 11 inches = 18 1/2 inches, smack dab in the middle of the recommendation. And a rise of 4 inches calls for a run that is between 13 and 16 inches.