How to build deck stairs
Set the landing, measure the total rise, cut one stringer and test it, then hang the stringers from the deck, anchor them at the bottom, and add treads, a handrail, and guards. Worked from a 42 in deck with the numbers computed by the app's stair solver.
Updated
Get the layout first
Every step below works from a riser height, a tread depth, and a riser count. Enter the deck's total rise and the deck stair calculator derives all three and checks them against IRC R311.7.
The short version
Build the landing pad first, because the total rise is measured plumb from the top of the decking down to it. Run that rise through a stair calculator for the riser count, riser height, and tread depth. Lay out one stringer with a framing square, drop its bottom by one tread thickness, and test it against the deck before cutting the rest from it as a pattern. Hang the stringers from the rim joist with stair hangers or a hanger board so the top riser matches every other riser, anchor the bottom to a kicker on the pad, then fasten treads, add a handrail once the stair has four or more risers, and add guards where the stair is more than 30 in above grade.
Step by step, worked from a 42 in deck
The top of the decking sits 42 in above the finished landing. The stair solver turns that into the layout in the table below; every figure is computed by the same code the app runs, not typed in. The deck surface is the top step, so the stringers carry one fewer tread than there are risers.
- 01
Set the landing before you measure
Pour a pad, set pavers on compacted gravel, or build a landing at the foot of the stair, as wide as the stair and at least 36 in deep in the direction of travel. Its top is the surface the total rise measures to, so it has to be at final height first. Pitch it slightly so water runs away from the stair.
- 02
Measure the total rise plumb
Run a straightedge and level out from the top of the decking to a point over the landing where the bottom step will sit, and measure straight down. Measuring at the deck's edge instead of out where the stair lands is the usual reason the bottom riser comes out wrong, because the ground falls away from the deck. Here that measurement is 42 in.
- 03
Run the numbers
Enter the 42 in rise in the calculator. It comes back with the riser count, riser height, and tread depth in the table below, all inside the IRC limits of a 7-3/4 in maximum riser and a 10 in minimum tread. Those two dimensions are your framing-square settings.
- 04
Lay out and cut one stringer
Clamp stair gauges on a framing square at the riser and tread, step off the notches on a straight 2x12, and mark the top plumb cut and the bottom level cut. Cut the bottom up by one tread thickness so the first and last risers finish equal once the treads go on. Stop each saw cut at the line and finish the corner with a handsaw so you do not overcut into the throat, the solid wood left under the notches. The app warns when that throat drops under 3-1/2 in, a common-practice minimum, since the IRC sets none.
- 05
Test it, then cut the rest from it
Hold the first stringer against the rim joist and set it on the landing. Check the treads with a level, then set a scrap of tread stock on the top notch and measure from it up to the deck surface: it must match the riser height. Once it fits, trace it onto the other boards so every stringer is identical. A 36 in stair on 2x6 treads usually takes three stringers; thinner decking wants them closer.
- 06
Hang the stringers from the deck
Fasten the top of each stringer to the rim joist or beam with metal stair stringer hangers, or to a hanger board through-bolted to the rim, using the fasteners the hanger maker lists. Toe-nails or a few deck screws alone are not a connection. Set the stringers so their top tread line sits one riser height plus one tread thickness below the deck surface, which mirrors the drop at the bottom. The deck is then the top step, as in this layout, and once the treads go on the top riser matches all the others.
- 07
Anchor the bottom
Fasten a ground-contact pressure-treated 2x4 kicker to the pad with concrete anchors, notch the stringer bottoms to fit over it, and screw or bolt them to it. The kicker keeps the stringers from sliding out at the foot. Keep untreated wood off the ground and use ground-contact lumber for anything that touches the pad.
- 08
Add treads, risers, handrail, and guards
Fasten the treads with a gap between boards for drainage, and add riser boards or sub-risers if the open gap between treads needs closing. Six risers means a handrail is required, and a 42 in deck is high enough that the open sides need guards. The code table below lists the limits.
Layout for a 42 in total rise
| Risers | 6 |
| Riser height | 7 in |
| Treads on the stringer | 5 |
| Tread depth | 11 in |
| Total run | 4 ft 7 in |
| Stringer length (diagonal) | 5 ft 9-3/16 in |
| Stair angle | 32.5° |
Each figure is rounded to the nearest 1/16 in for the tape. The total run is how far the stair reaches out from the rim, so the landing has to start there. The stringer length is the diagonal of the flight, not the board to buy: add for the top and bottom cuts, then go to the next stock length up.
The code limits a deck stair has to meet
These are 2021 IRC residential provisions. The riser and tread limits come from the calculator; these are the rest of the stair. Your jurisdiction may amend them, so confirm with the building department before you build.
| Item | Limit | Reference |
|---|---|---|
| Handrail required | 4 or more risers | IRC R311.7.8 |
| Handrail height | 34 to 38 in above the nosings | IRC R311.7.8.1 |
| Guard required | open side over 30 in above grade | IRC R312.1.1 |
| Guard height on a stair | 34 in min above the nosings | IRC R312.1.2 |
| Guard opening on a stair | blocks a 4-3/8 in sphere | IRC R312.1.3 |
| Open riser gap, rise over 30 in | blocks a 4 in sphere | IRC R311.7.5.1 |
| Nosing, solid risers | 3/4 to 1-1/4 in, unless the tread is 11 in or deeper | IRC R311.7.5.3 |
Common questions
- How do you attach deck stairs to the deck?
- Hang the stringers from the rim joist or beam with metal stair stringer hangers, or bolt a hanger board to the rim and fasten the stringers to it. Use the fasteners the hanger maker specifies. The goal is a connection that carries the stair's weight in shear, which toe-nails and a few screws do not.
- Do deck stairs need a concrete pad?
- They need a stable, level landing that will not settle or wash out. A concrete pad is the most common, but pavers on compacted gravel or a framed landing also work. Set it before measuring, since the total rise is measured to its top.
- Is the top step the deck or one step down?
- In this layout the deck surface is the top step, so a stair with six risers has five treads on the stringers. The stringers' top tread line sits one riser height plus one tread thickness below the deck surface, so the finished top riser matches the rest. If your stair starts with a full tread at deck height instead, add one tread to the run and keep the riser height the same.
- When do deck stairs need a handrail?
- Under the 2021 IRC, once the flight has four or more risers. The handrail goes on at least one side, 34 to 38 in above the tread nosings. A three-riser stair needs none by the IRC, though one is still easier on knees and in the dark.
- Why measure the rise out where the stair lands?
- Because the ground usually falls away from a deck. The drop at the deck's edge is shorter than the drop where the bottom step actually sits, and building to the shorter number leaves the bottom riser tall.
Take the stringer plan to the saw
The app derives the whole deck stair from one total rise, checks it against IRC R311.7, and prints the stringer with every notch dimensioned, plus a baluster layout for the guard.
See also