I cut my first set of stair jacks (or stringers, as they’re called in other parts of the country) some 39 years ago. Since then, I have frequently come across stairs that are too steep, too narrow, or too long, or that just don’t complement the deck they’re attached to.

When I build stairs, I focus on safety, comfort, and appearance. Achieving the first two is a fairly simple matter of following basic guidelines; building stairs to be visually inviting is a little more complex. In this article, I’ll talk about these three principles, plus a few other practical matters.

Build Better Than Code

A staircase should do more than simply provide a means to get from the ground to the deck or from one deck level to the next. Stairs should make you want to see where they lead, and they should be more comfortable and convenient than code-minimum design makes them. Too often, though, they are aesthetically boring, or worse, uncomfortable or even downright dangerous.

According to Consumer Product Safety Commission reports, more people are injured on stairs than in any other place in the home. In part, I think that’s because most stairs are steeper than they need to be. The greater the rise, the more likely someone will trip when going up the stairs, by kicking the next riser or catching a toe. And when treads are shallow, people are more likely to miss a step, whether they’re going up or down.

One of the main reasons steep stairs are so common is cost: Steep, narrow stairs use shorter stringers and less tread and riser material. But a good stair is designed for a gradual and easy climb. Adding one more tread doesn’t cost very much and can make a huge difference in how the stairs feel and perform.

Stairs that aren’t as steep will be longer, though, and a long flight of stairs can look intimidating. One of the simplest ways to scale down the appearance of a stair is to add landings. There should be no more than eight risers between them — even fewer is better. The landings must be at least as wide as the stair and at least 36 inches deep.

It’s also important to consider the width of the stairs. To transform an otherwise ordinary-looking deck into an inviting showpiece, widen the stairs. They need to be at least 3 feet wide to satisfy code requirements, but increasing that measurement to 5 feet or more will allow two people to use the stair at the same time and give the deck an open feel. Making the bottom tread a foot wider than the rest of the stairs can make the staircase look even more gracious for little extra expense.

For both appearance and safety, consider differentiating the steps. Make the treads a different color from the main deck, use a different color for the riser facing, or change the decking direction on one or more treads. The idea is to make the steps more visible and thereby safer to use.

Ideal Tread and Riser Measurements

For a comfortable tread-to-riser relationship, 18 inches is the magic number. That’s what the tread depth and the riser height should add up to. You can use a 4-inch rise with a 14-inch tread, or a 7-inch rise with an 11-inch tread, or some other combination that adds up to about 18 inches. Once the tread and rise add up to about 2 inches more or less than that, stairs will feel funny to climb.

Getting stairs right is a combination of comfortable geometry, and sturdy, durable construction details.
Chuck Lockhart Getting stairs right is a combination of comfortable geometry, and sturdy, durable construction details.

For the purpose of figuring out how far a stair jack will project from the deck, add together the depths of all the treads. For example, if a stair has four treads with a tread depth of 10 inches, the bottom face of the stair jacks will be 40 inches out from the deck. To this, you’d also have to add the thickness of one riser, and the amount the bottom tread overhangs the bottom riser, to get the total distance the stair extends.

The minimum tread depth — or the length of the level cut in the jack (stringer) — in the IRC is 10 inches. The tread itself will be deeper, as it needs to overhang the riser by 1 inch. So if you have a 10-inch tread depth, the actual tread will measure 11 inches.

The 300-pound point load mentioned in the code relates directly to the tread material (usually decking) and the spacing between jacks. The stronger the decking, the greater the allowable space between the jacks, and the fewer jacks you’ll need to cut.
The 300-pound point load mentioned in the code relates directly to the tread material (usually decking) and the spacing between jacks. The stronger the decking, the greater the allowable space between the jacks, and the fewer jacks you’ll need to cut.

Calculating Stair Jacks

To start laying out a flight of stairs, I field-measure from the finished deck height to the finished landing level. In most cases, you can do this by measuring from the ground up to a level held on the deck framing. Be careful, though, as this is where many mistakes are made. If you measure before the decking is laid or the landing pad is poured, you’ll need to account for those thicknesses. Also, pay attention to any slope and make sure you measure to the correct side of the level.

Once you’re sure your measurement is accurate, divide it by 7 inches (a typical riser height) to give an approximate number of risers. For example, the distance from the finished deck to the finished landing might be 3 feet 2 11/16 inches (38.675 inches). When you divide that by 7 inches, you end up with 5.525 risers. If you round down to 5, the math would be 38.675/5 = 7.735, giving you a riser height of 7 3/4 inches. Or you could round up to 6, in which case the riser height would be 67/16 inches (38.675/6 = 6.44). In this example, I would opt for six risers to better fit my design guidelines, as long as the stair would not protrude too far into other design elements.

Here’s another example: The distance from the finished deck height to the finished landing level is 8 feet 63/8 inches, or 102.375 inches. Dividing by 7 inches yields 14.625. If you round up to 15 risers, the riser height will need to be 6 13/16 inches (102.375/15 = 6.825). I would break up the stair into two flights, one with seven risers and one with eight. The middle landing would then be 4 feet 8 5/8 inches from either the deck or the bottom landing, depending on whether the eight-riser flight was the upper or lower one.

Note: There will always be one more riser in a flight of stairs than there are treads.

Laying Out and Cutting Stair Jacks

Once you’ve calculated the rise and run, it’s time to cut the stair jacks (stringers). Lay a pressure-treated 2x12 on a set of saw horses and use a framing square to lay out the risers and treads. Place the square on the board such that the measurements for the riser on one leg and the tread on the other align with the edge of the 2x12. Pencil a line along the outside of the square, making it very dark so it will be easy to see when you’re cutting. After laying out the first tread and riser, measure from the bottom edge of the stringer to the inside of the notch — this measurement should be at least 5 inches to ensure the stringer’s strength.

Move the square down the board and mark the next riser and tread; continue in this manner until all the risers and treads are laid out.

The bottom cut, where the stringer will rest on the landing, is laid out parallel with the bottom tread; instead of measuring the full rise, this last riser should be shorter than the others by the thickness of the tread material. So if you are using one-inch decking for the treads, the bottom riser will be one inch shorter than the rest. This drops the entire jack by the tread thickness, but the difference is made up for when the treads are installed.

At the jack’s top, mark a line down square from the back of the top tread. This marks where the jack will attach to the deck framing. Cut the first stair jack precisely, leaving the layout lines. When cutting the heel of the tread, do not overcut, as that will weaken the stair jacks and they won’t be able to span as far as they should. Cut to the line and use a hand saw to cut the notches out.

Use this first jack as a pattern to mark the rest of the jacks. But first — using a level on the tread — check to make sure it fits perfectly at the top and bottom. If it’s not perfect, try again.

When cutting the rest of the jacks, cut to take out the layout line. This will make the stair jacks more uniform. In the finish stage, I always cover the visible stair jacks with a fascia of the same finish material I use on the deck. So before I install the jacks, I use them as a pattern to scribe this fascia.

Another thing I do before installing the jacks is treat the wood that was exposed by cutting with an end-cut solution. I like to use an oil-based solution that’s 25 percent copper naphthenate. If the jacks are going to sit on a concrete slab, cut 1/2 inch more off the bottom of the jacks and install a scrap piece of 1/2-inch composite or PVC fascia to hold the jacks off the concrete — it will make them last longer.

Connecting the Stair to the Deck

There will need to be some support at the deck for the stair jacks to attach to — they will be too low to simply attach them to the outer joist. Using bolts or structural screws, I attach some 2-by hangers down the back side of the rim joist and attach a 2x8 to them below the rim joist. This board will be the same size as the width of the stairs.

Use a level to make sure that all the jacks are level at the bottom and that each jack is sitting evenly with the landing. If it isn’t, scribe the bottom to the landing; otherwise, over time it will cause the last tread to break off.

To install the jacks, I use USP CSH-TZ (800/328-5934, uspconnectors.com) or Simpson LSC hangers (800/999-5099, strongtie.com). Nail the hanger to the board under the rim at the right height so that the bend will cradle the stair jack. Nail the jack to the correct height. The jacks also need to be securely attached to the landing. If the “landing” is another section of deck, each jack can be screwed through the decking from underneath.

Before you install the treads, think about how the railing will be attached. If blocking is needed to support the posts, it will be a lot easier to install when the stairs are still open. Once that’s done, I install the treads, which are sized to overhang the fascia 1 inch on each side.

Deck stairs are often not straightforward. Take the time to think through them, follow the basics, and be accurate in your cutting.

Kim Katwijk, a deck builder in Olympia, Wash., and his wife, Linda Katwijk, are frequent contributors to the magazine.