Stairs

What it's for

Laying out a straight flight of stairs. You give it the floor-to-floor rise, or the run, or both, and it gives you the riser count, the riser and tread you cut to, the stringer length to lay out and the length to order, the stairwell opening the headroom needs, a section drawing, a stringer board with every notch marked, a running mark-out tape and a material list. It checks the stair's width, headroom, flight rise, risers, treads and nosing against IRC R311.7.1, .2, .3 and .5, and its cut stringers against the AWC deck guide's span and throat, and prints any failure in red. It does not check landings, handrails or guards: the results say so.

Step by step

This example uses the numbers the screen opens with, so your screen matches the shots.

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1. INPUT MODE — leave it on By Height. You know the rise and the riser you want. The other three modes are covered below.
2. TOTAL RISE — measure plumb from the finished lower floor to the finished upper floor. If the finish floors are not down yet, add or take off their thickness first. The example is 9' 0".
3. TARGET RISER HEIGHT — the riser you would like. The example is 7".
4. RISER ROUNDING — the rise rarely divides evenly by your target. Riser Limited rounds the count up, so no riser comes out taller than your target. Nearest rounds to the closest whole count. That can save a riser, but the riser can come out taller than you asked for.
5. LEFTOVER RISE — the risers are cut to the 1/16" a tape reads, and a rise seldom splits into equal 1/16" risers. Spread, the setting the screen opens on, puts each tread at its own share of the rise, to the 1/16". The risers come out in two heights 1/16" apart, mixed up the flight, and they add up to the rise exactly: 10' 6-3/8" in 19 risers is 8 at 6-11/16" and 11 at 6-5/8". Bottom riser is the layout handheld stair calculators use: every riser cut the same, with the whole leftover in the bottom riser. At 10' 6-3/8" that bottom riser finishes 7-1/8" against 6-5/8", which is more than the 3/8" the code allows.
6. TREAD DEPTH — the level run of one step. The total run is this times the number of treads. The example is 10-1/2".
7. NOSING is how far the front of the tread hangs over the riser below. TARGET HEADROOM is the clear height you want over the stair, measured plumb from the sloped line along the nosings. STAIR WIDTH is the width of the flight. UPPER FLOOR THICKNESS is the thickness of the whole upper floor assembly. The opening the stair needs is worked out from it.

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8. If the hole in the floor is already framed, turn on STAIRWELL OPENING and enter OPENING LENGTH, measured level, back from the face of the top riser. The headroom is then worked out from it. If you have taped the real clearance on site, turn on MEASURED HEADROOM and enter it. A measured figure is used for the code check ahead of a worked-out one. The example leaves both off.
9. RISER TYPE — Closed, the example's setting, takes riser boards, and the material list buys them. Open leaves the gap between treads open, and the code check then measures that gap.
10. STRINGERS is how many you are cutting. On an exterior stair the screen raises it when the width needs more (see below). TREAD STOCK sets the tread thickness, which is what the bottom riser is dropped by. RISER STOCK is the thickness of the riser boards.
11. AUTO SUPPORTS — a cut stringer may span no more than 6' 0" measured level (AWC DCA 6, Figure 28). With it on, the screen puts in the fewest support lines that keep every span within that, spaces them evenly, draws a post at each and buys the posts. The example's 13' 1-1/2" run gets 2, at 4' 4-1/2" on centre. Turn it off to set SUPPORT LINES yourself: 0 means the stringers span end to end. A support line is a 4x4 post under each stringer on a footing, a bearing wall under them, or a framed landing.
12. EXTERIOR (DECK) STAIR — turn it on for a stair off a deck or porch. The AWC deck guide's rules then apply: 2x12 cut stringers only; at least three stringers no more than 18" apart on centre, so the count grows with the width (a 3' 6" stair takes 4); a rise over 12' 0" needs an intermediate landing; a sloped hanger of at least 625 lb at the top of each stringer, which the material list buys; and four notes in BASIS: treated lumber, galvanized or stainless fasteners, a footing at grade, and a light at the top.
13. WASTE FACTOR — the extra you buy over the measured quantity.
14. Read the answer: 16 risers · cut 6-3/4". The example is within every limit it checks. Switch RISER TYPE to Open and a red flag appears: 6-3/4" less the 1" tread leaves a 5-3/4" gap, and a 4" sphere goes through it.

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The other input modes

• By Count — you choose the number of risers. RISERS replaces the riser target and the rounding choice.
• By Run — you only know the run. Enter TOTAL RUN, measured level from the foot of the stair to the face of the top riser, with TARGET RISER HEIGHT and TARGET TREAD DEPTH. There is no rise field in this mode. The rise is worked out for you.
• Rise+Run — both are fixed. Enter TOTAL RISE and TOTAL RUN. There is no tread field in this mode. The tread is the run divided by the number of treads.

Reading the results

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1. The headline is the riser count and the riser you cut to, cut 6-3/4" in the example. It is on the 1/16" grid, so it is exact. When the rise does not split evenly, the spread gives two riser heights, and the headline names both with how many of each: 19 risers · 8 @ 6-11/16" + 11 @ 6-5/8" for 10' 6-3/8". The chips below show the average riser, rise divided by count, which is why they can carry ≈. The bottom riser is different: see Bottom riser cut. The sample tag means you have not entered anything of your own yet.
2. The chips show one riser fewer, the current count, and one more, each with its riser height and its verdict. Tap a chip to take that count. The screen switches to By Count. A chip past the RISERS row's range of 2 to 30 is dimmed and does nothing when tapped.
3. The lines under the chips. Tread, rise, run and the incline in degrees. R+/– and T+/– are what rounding to 1/16" leaves over the whole flight. They print bold when they are not zero. With the rise spread, R+/– is 0: the leftover is already shared out. Bottom riser cut is the first riser you cut. It is shorter than the riser it finishes at by the tread thickness, and on Bottom riser by the R+/– as well. The drop, the amount you take off the foot of the stringer after laying it out, is the cut riser less the bottom riser cut. With the rise spread it is just the tread thickness, 1" on 5/4 stock. On Bottom riser, with a 7-1/8" riser and a 6-1/2" bottom riser cut, it is 5/8". The mark-out card, both drawings and the 1:1 template print that same figure. Stringer LAYOUT is the finished length, nose 1 to the top cut, that you lay out on the board. ORDER is the tip-to-tip length of the board, with the board size after it. Cut the board to ORDER, not to LAYOUT: the mark-out hooks the heel of the bottom cut, a full step below nose 1, so a board cut to the layout length has nothing to hook. The cut list, the section drawing (STRG 2x12 LAYOUT … BOARD …) and OPTIMIZE all carry the tip-to-tip board. Stringers gives the count you build and how far apart their centres are, and says when an exterior stair raised the count. The supports line gives the support lines and their spacing, Auto supports: 2 lines at 4' 4-1/2" o.c. — each stringer span ≤ 6' 0" in the example. An exterior stair adds a line naming the deck guide's rules. Opening req'd is the stairwell opening that gives your target headroom, nosing included. It is a minimum, so it is rounded up to the next 1/16": type it back in as the opening and the check passes. Headroom is owed over the stair and over the 36" landing at its foot (IRC R311.7.2 and R311.7.6). When the floor above sits lower than your target headroom, no opening over the stair can clear it, so the line gives the opening that clears the stair and that landing instead, and BASIS says how thin the floor above would have to be for a shorter one. The last line, right above the check, says what holds the stringers up: Cut stringers must bear on a wall, post or landing at least every 6' horizontally (AWC DCA 6), or be engineered. The cut sheet prints it under the check as well.
4. The check. A stair with nothing wrong says in green what it was checked against. Until you give an opening or a measured headroom it reads Headroom, landings and handrails not checked — within IRC 2021 R311.7.1, .3, .5 limits — check local code: the width, the rise of the flight, and the risers, treads and nosing. A stringer span over 6' 0" between supports fails, because a cut stringer may span no more than that horizontally (AWC DCA 6, Figure 28). Once the headroom is checked too it reads Landings and handrails not checked — within IRC 2021 R311.7.1–.3, .5 limits — check local code. Landings, handrails and guards are never checked: the screen has no input for them. The line above the check lists them with their code sections — the landing at the top and bottom, 36" deep (IRC R311.7.6), the landing at an exterior door (R311.3), a handrail at 4 or more risers (R311.7.8) and guards over 30" (R312.1) — and the cut sheet prints it as Not Checked. Otherwise each failure gets its own RED LINE IN CAPITALS, with the number that failed and the code section it was checked against. There can be several at once. Fix every one.
5. BASIS & WHAT WAS ASSUMED — tap it. It opens the rounding rule, how the opening was worked out, the headroom note, how the riser count was rounded, the bottom riser drop, the stringer throat, the code edition the checks use and a reminder to check your local code. If you have not given an opening or a measured headroom, the headroom note tells you to check it on site.
6. The drawing is the stair in section with the same numbers on it, and one step enlarged in the corner. Pinch to zoom, drag to pan, double-tap to reset. The expand button opens it full screen. A stair that fails a check carries the failure on the drawing as well, named in red — two of them, and then a line saying how many more there are and to read the checks list. See Reading the drawing.

What clears each flag:

• Open riser gap — a gap of 4" or more lets a 4" sphere through, so the gap has to be under 4". Set RISER TYPE to Closed, or use more risers.
• Flight rise — one flight may rise no more than 12' 7" between floors or landings (IRC R311.7.3). This screen lays out a single flight, so a taller rise needs a landing. Work out each flight on its own, with the rise from the floor to the landing and from the landing up.
• Riser too tall — lower TARGET RISER HEIGHT, tap the chip with one more riser, or go back to Riser Limited.
• Riser height too short — raise TARGET RISER HEIGHT, or tap the chip with one fewer riser.
• Riser variation — only on Bottom riser: the leftover is too much for one riser to take. Set LEFTOVER RISE to Spread, or tap a chip with a different count. A spread stair never trips it, because no riser is more than 1/16" off another.
• Tread depth — raise TREAD DEPTH, or in a run mode lengthen TOTAL RUN.
• Stair width — raise STAIR WIDTH.
• Nosing — change NOSING or deepen the tread.
• Headroom — lengthen the opening, or re-measure. An opening that reaches 36" past the bottom riser clears the stair and its landing, and the check passes.
• Stringer throat — too little wood is left under the notches. The flag says what to do.
• Cut stringer span — a span between supports is over 6' 0", the most a cut stringer may span horizontally (AWC DCA 6, Figure 28). The flag says how many supports to add. Turn on AUTO SUPPORTS or raise SUPPORT LINES, or have the stringers engineered. A stringer nailed to a wall is held on that side only; the middle and open-side stringers still span free. With a landing, work out each flight on its own.
• Deck stair rise — exterior only: the deck guide wants an intermediate landing on a stair that rises more than 12' 0". Work out each flight to the landing on its own.

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7. STRINGER BOARD — NOTCH SET-OUT is the same stringer lying flat on the horses. It shows the tip-to-tip length, the square settings, the drop on the first riser, the throat, and the running distance to every nose.
8. RUNNING MARK-OUT lists those distances one at a time so you hook the tape once and mark down the board. Pick the tape: NOTCHED, HOUSED or STORY POLE. HOUSED is for a routed stringer, laid out on a nosing line 1-1/2" in from the top edge; its note gives the plunge, the wedge taper and the board width the housings need. On an exterior stair it adds that the deck guide (DCA 6) has no routed stringer. On a spread stair, mark every station off the one hook. The marks carry the two riser heights; the square only sets the angle. The story pole shows which tread gets which.
9. The speaker reads the marks aloud. See Mark-out and speak.

Below the mark-out is the notching template card. It prints one notch at true size, across more than one sheet if the tread is wider than the page. On a spread stair the notch is the exact share of the rise, ≈ 6-5/8" for 10' 6-3/8" in 19 — the same figure as the square setting, drawn true — so trace it at each NOTCHED mark. If the riser is taller than the page it prints the set-out numbers instead, and the card says so before you print. Print at 100% scale. Do not fit to page. Then comes MATERIALS: stringers, treads and riser boards, with the waste factor in the quantities. A tread board runs from the nose back to the riser above, so it has to be as wide as the tread plus the nosing. Both tread stocks are 11-1/4" wide; when the tread and nosing come to more, the Treads row and a bold line in the results say so (a 12" tread with a 3/4" nosing needs 12-3/4"). Stringers are bought at the next even-foot length, the lengths the yard stocks, and OPTIMIZE starts from that same length. The riser row is there because the screen opens on Closed; on Open there are no riser boards to buy and the row goes. With support lines there is a 4x4 stringer posts row, one under each stringer at each line; cut each to fit on site, and skip the ones a wall or landing replaces. Indoors a post stands on floor framing built for its load, with no footing (IRC R301.1, a load path to the foundation); on an exterior stair the note gives the footing and bolts from AWC DCA 6. An exterior stair adds Stringer hangers (sloped, 625 lb min), one per stringer, and Stair posts at grade (4x4), one under each stringer where the stair meets the ground, on a footing below frost with the stringer on a 2x4 bearing block (AWC DCA 6, Figure 34). Indoors there is a Kicker plate (2x4) at the stair width to hold the stringers' feet, and BASIS says how the stringers hang at the header. With 4 or more risers the list buys a Handrail for one side (IRC R311.7.8), long enough to run over the nosings from the lowest riser to the top one, plus its Handrail brackets at no more than 48" apart. The cut sheet prints the support lines with their distances from the bottom riser face.

At the bottom, CUT SHEET, the list icon at its right end, CUT LIST, SEND LIST and OPTIMIZE stay dim until you change at least one input, so a sheet made from the sample numbers never reaches a job. SAVE stays lit, but while every input is still a default a tap only answers Enter your job's numbers first and saves nothing. CUT SHEET makes a PDF with both drawings and every input you set. It opens with the same check line the screen shows, such as Headroom, landings and handrails not checked, then the cut figures, then your inputs, then the notes; what does not fit the first page carries on to the next. SAVE keeps the result in History, CUT LIST puts the list on the Lock Screen, SEND LIST sends a checkable list to another phone, and OPTIMIZE sends the stringers to the Cut List Optimizer at their order length. A stringer over 24' is longer than any single stock, and a line under the buttons says so before you send.

SPACE THE BALUSTERS, under the results, opens Baluster Spacing for the guard on the open side: the stair's total run becomes the opening and its tread run the TREAD RUN, with STAIR GUARD on, so you do not retype them.

Common mistakes

• Measuring the rise off the subfloor. TOTAL RISE is finished floor to finished floor. If finish flooring is still to go down on either level, allow for it before you enter the rise.
• Cutting the board to the layout length. The layout length is the finished stringer, laid out on the board. Cut the board to ORDER, tip to tip, then lay out; the material list rounds the buy up to the next even foot.
• Cutting every riser the same. The bottom riser is shorter. Cut it to Bottom riser cut, not to the headline height.
• Stepping the square on a spread stair. Stepping one 1/16" setting up the board puts the flight off at the top, 1/2" short at 10' 6-3/8" in 19. Mark the NOTCHED stations from the one hook instead.
• Overcutting the notches. A saw cut run past the inside corner of a notch cuts into the throat the stringer is sized on. Stop each cut at the corner and finish it with a hand saw; the NOTCHED note says so too.
• Taking a cut stringer as a free-spanning beam. The screen sizes the stringer for its notches (the 5" throat), not for the load. It needs a bearing every 6' 0" horizontally, or an engineer. The posts AUTO SUPPORTS draws are part of the answer: build them.
• Leaving EXTERIOR off on a deck stair. Indoors the screen allows a 2x10 and any stringer spacing; outdoors the deck guide does not.
• Taking the green line as a headroom pass. With no opening and no measured headroom, the headroom has not been checked, and the green line says so. Measure it on site, or enter the opening.

Related

• Baluster Spacing
• Deck
• Cut List Optimizer
• Reading the drawing
• Mark-out and speak
• Cut sheets and 1:1 templates
• Cut list on the Lock Screen
• Send to the Cut List Optimizer
• Saving and History