The idea of building stairs, even if it is just a few steps up to a deck or porch, is enough to instill fear in most do-it-yourselfers. There are just so many things that can go wrong.
The hard thing about building stairs is calculating the rise and run of each step. For stairs to be comfortable to use, every step must rise the same vertically and run the same horizontally. And the stairs have to fit perfectly in the space total vertical space allotted for them. That is, they have to rest on deck floor or slab at the bottom and the deck surface or landing at the top. It usually takes a lot of "something divided into something" to figure out the exact rise and run. Cutting the steps, which essentially run diagonally, out of a straight board to make the supporting stringers can be pretty tricky as well.
But you can use pre-cut pressure-treated stair stringers.
"It's much simpler for a homeowner to use pre-cuts, instead of having to calculate exact cuts and cut a 2-by-12 to make stringers," said Chris Doerfler, contractor sales representative at Lumber in Fallston.
At 84 Lumber, he said, pre-cut stringers are available in 3-, 4- or 5-step sizes. All the risers are 7 inches and all the runs are cut to accommodate two 5 1/2 -inch wide treads. Prices per stringer range from $5.84 for a 3-step to $9.84 for a 5-step.
Stairs need to be supported about every 2 feet. A set of steps 3 feet wide would need three stringers, one at each side and one in the middle. Wider stairs would need more stringers, at intervals of 2 feet.
While using the pre-cut stringers is easier than figuring and making the cuts yourself, there is one trick. Even the pre-cuts have to fit the total vertical space allotted. A 3-step stringer has a rise of 21 inches (3 times 7 inches), a 4-step a rise of 28 inches (4 times 7 inches) and so on.
That means the distance from the floor or slab under the bottom riser to the level of the landing or deck has to be 21, 28 or 35 inches.
You can adjust the bottom level to some extent if you're ending up on a concrete pad in the yard: Just pour the slab to the desired height.
If you're ending up on a floor, however, the heights have to match. And if they don't, you can't use pre-cuts. It's something to think about if you are designing your own deck, and if you want a deck with multiple levels. If you design it to use pre-cut stairs, you'll save a lot of time.
How do you figure out how high the steps need to be? Hold a level, if you have one long enough, or a 2 by 4 with a level on top, on the framing of the deck (remember the deck will have a floor and the stairs will have a tread) and out over the edge to where the steps will end. Measure down from there.
If the distance is, say, 39 inches, you can use a 5-step pre-cut stringer and pour a 4-inch-thick concrete slab at the bottom in the yard. Level the slab so the distance to the top of the framing is 35 inches. You can also adjust the grade of the yard to add a couple of inches, if you need it.
The most efficient way to build a small stair unit is to assemble it all but the treads. Level it to the deck framing and bolt it in. It will be sitting on a level slab, so that should level it up. Then install the treads.
If you're in a hurry to get the stairs done, rest the bottom of the bottom riser partly on the wooden form for the concrete slab. That way you don't have to wait for the concrete to set up before you install the steps. When you strip the form out later, the stairs will still be resting on the concrete.