How to Build Deck Stairs: Rise, Run, and the Requirements That Govern Them

Table of Contents

1. Introduction
2. The Geometry Is the Whole Job
3. Calculating Rise and Run
4. The Uniformity Rule
5. The Bottom Step Mistake
6. Stringer Layout, Spacing, and Throat Depth
7. Attaching Stringers Properly
8. The Landing Is Structural
9. Handrails Are Required, Not Decorative
10. Guards and the Openings Rule
11. Materials, Traction, and Wisconsin Winters
12. Frost Movement at the Bottom of the Stairs
13. Inspection and What Gets Checked
14. Conclusion
15. Get Your Stairs Built Right
16. Frequently Asked Questions

Key Takeaways

• Riser height and tread depth have limits, commonly around seven and three quarter inches maximum rise and ten inches minimum tread. Confirm the figures your municipality inspects to.
• Within one flight, the tallest and shortest riser may not differ by more than roughly three eighths of an inch. This is the most commonly failed stair requirement.
• Divide total rise by the number of risers rather than choosing a riser height and hoping it divides evenly.
• Cut the bottom of the stringer down by one tread thickness, or the bottom riser ends up taller than every other one.
• Stringers need proper connection hardware at the top. Screws into end grain are not an adequate connection.
• Stairs need a solid landing at the bottom, at least as wide as the stairs and typically thirty six inches deep. Stringers cannot sit on soil.
• Four or more risers generally requires a handrail at a specified height with a graspable profile. It is a safety requirement, not a design choice.
  

Introduction

Deck stairs are built from two numbers: the rise of each step and the depth of each tread. Get those right, keep every riser in the flight within about three eighths of an inch of each other, and most of the rest follows. Get them wrong and the stairs are both a code failure and a genuine hazard, because people fall on stairs that are not uniform.

That is a narrower framing than most guides on this subject use, and it reflects where the difficulty actually is. Cutting stringers is straightforward carpentry. Working out the geometry so the flight lands correctly at the bottom, every riser matches, and the whole thing meets the requirements is the part that takes care.

The safety stakes are not abstract. Your foot calibrates to the first step and expects every subsequent one to be identical. A riser an inch out of line is a trip you do not see coming, and stairs are where deck injuries concentrate.

What follows covers the calculation, the layout errors that produce uneven steps, how stringers actually get attached, and the handrail and guard requirements. Whether you are building or evaluating, these are the things to check. And if it is going to a contractor as part of a larger deck building project, they are worth understanding well enough to ask about.

Figures throughout reflect widely adopted requirements. Wisconsin administers its own dwelling code and your municipality inspects to it, so confirm specifics locally before cutting anything.

The Geometry Is the Whole Job

Three terms, used precisely:

Rise is the vertical height of one step, measured from the top of one tread to the top of the next.

Run is the horizontal depth of one step, and tread depth is what you actually stand on, measured from nosing to nosing.

Total rise is the full vertical distance from the deck surface down to the finished landing surface.

The limits, commonly applied:

• Maximum riser height of around seven and three quarter inches, with some jurisdictions permitting eight.
• Minimum tread depth of around ten inches.
• Maximum variation between the tallest and shortest riser in a flight of about three eighths of an inch, and the same for tread depth.

Why the maximums exist. A rise that is too tall is tiring going up and unsafe coming down. A tread that is too shallow does not accommodate a foot, so people descend on the balls of their feet with their heels overhanging.

Comfortable is different from compliant. Stairs at the maximum rise and minimum tread meet the requirement and feel steep. Something closer to a seven inch rise with an eleven inch tread is noticeably more comfortable to use, if you have the horizontal room for it. Deeper treads mean the stairs project further into the yard, which is the trade.

Calculating Rise and Run

The sequence that produces uniform steps, worked in the correct order.

Step one: measure total rise accurately. From the top of the deck surface down to the finished surface of the landing. Not to the current ground, but to where the concrete pad or pavers will actually sit once built. Getting this wrong at the start throws off everything else.

Measure by running a level line out from the deck edge to a point above the landing location and measuring down. Do not measure down the face of the deck, since the ground is rarely level with where the landing will be.

Step two: divide to find the number of risers. Take the total rise and divide it by your target riser height. If total rise is fifty inches and you target seven inches, that gives roughly seven point one. Round to a whole number, so seven risers.

Step three: divide back to get the actual rise. Fifty divided by seven is about seven and one eighth inches per riser. That is your actual rise, and every riser gets it.

This order matters. Choosing a riser height first and hoping it divides evenly into the total is how flights end up with an odd step at one end. The number of risers is a whole number, so the rise per riser is whatever the division produces.

Step four: treads are always one fewer than risers. A flight with seven risers has six treads, because the deck surface itself serves as the top landing.

Step five: work out total run. Number of treads multiplied by tread depth. Six treads at eleven inches is sixty six inches of horizontal projection, plus the landing beyond it. Check that the stairs fit where you intend them to go and clear setbacks and obstacles.

Step six: check both figures against the limits before cutting anything.

If the numbers do not work, the options are adding a riser to reduce the rise per step, adjusting the deck height slightly, or building a landing partway down and turning the flight. Forcing an out of range riser is not one of the options.

The Uniformity Rule

Worth its own section because it is the requirement most often failed and the one most connected to actual injuries.

Every riser in a flight must be within about three eighths of an inch of every other riser. Same for tread depth. This is not a target for the average, it is the maximum spread between the largest and smallest.

Why it matters more than the maximum height. People descend stairs on autopilot. After one or two steps the foot has learned the rhythm and stops looking. A riser that differs noticeably breaks that expectation at the moment weight is committed, and that is the mechanism behind most stair falls.

Where the variation creeps in:

• The bottom step, covered in the next section, which is the dominant cause
• An uneven landing surface, so the effective bottom rise differs across the width of the stairs
• Stringers cut individually rather than from a single template
• Tread material of inconsistent thickness
• A landing that settles after the stairs are built, which is a frost and drainage problem

How to avoid it: cut one stringer carefully, verify it in place, then use it as the pattern for every other stringer. Do not lay out each one independently.

The Bottom Step Mistake

The classic stringer error, and the reason so many DIY stairs have one odd step at the bottom.

The problem. When you lay out a stringer, the notches give you the rise from the top of one tread to the top of the next. But at the top of the flight, the stringer connects to the deck and the deck surface is the tread. At the bottom, the stringer sits directly on the landing and then a tread is placed on the lowest notch.

That means the bottom step ends up taller than the others by exactly the thickness of the tread material, unless you compensate.

The fix. Cut the bottom of the stringer down by the thickness of one tread. If your treads are one and a quarter inches thick, remove one and a quarter inches from the bottom of the stringer.

Common variations that catch people out:

• Two by six treads used flat have a different thickness than a nominal one inch board, and composite treads differ again. Measure the actual material rather than assuming.
• A stringer connector or bracket at the base adds its own thickness to account for.
• The landing surface itself must be at the finished elevation used in the calculation. If the pad ends up an inch higher or lower than planned, every riser calculation is off.

Check before you commit. Dry fit one stringer in position, measure the actual rise of the bottom step and the top step, and confirm both match the middle. It is a five minute check that prevents recutting the whole set.

Stringer Layout, Spacing, and Throat Depth

Stringer spacing is commonly a maximum of sixteen inches on centre for standard wood treads, and twelve inches or less for many composite and PVC tread products. Check the tread manufacturer's requirement, since composite is more flexible than wood and will feel bouncy at wider spacing.

Wider stairs need more stringers. A set of stairs thirty six inches wide needs at least three stringers at sixteen inch centres, and four is common. Two stringers on a wide flight is not adequate.

Throat depth is the amount of solid material remaining behind the notches. Cutting a two by twelve into stair notches removes a great deal of material, and what remains is what carries the load. Guidance commonly calls for at least five inches of solid material below the notch. Cut too deep and the stringer is weakened at the notch corners, which is where cracks start.

Cut stringers versus solid stringers. A cut or notched stringer has the steps sawn into it. A solid stringer is left uncut, with treads carried on metal brackets or wood cleats fastened to the face. Solid stringers retain full strength and are worth considering on longer flights or where load is a concern, though they read differently visually.

Cutting notes:

• Use a framing square with stair gauges set to your rise and run so every notch is identical
• Do not overcut the corners with a circular saw, finish them with a handsaw, since overcuts weaken the notch
• Seal every cut with end cut preservative, because notching exposes untreated interior wood on treated lumber
• Cut one, test fit, then trace the rest

Attaching Stringers Properly

The connection the original guidance handles with "galvanized screws or nails," which is not adequate.

What the connection carries. The full live load of everyone on the stairs, transferred into the deck at the top of the stringers. That is a real load in a location where it is easy to get wrong.

Screws or nails into end grain are not a structural connection. End grain holds fasteners poorly, and this is a shear situation.

Acceptable approaches:

• Stringer connector hardware made for the purpose, fastening the stringer to the deck rim or header
• A header or ledger securely fastened to the deck framing, with the stringers hung from it using appropriate hangers
• A notched top connection where the stringer bears on a support rather than hanging from fasteners

Bearing is better than hanging. Wherever the design allows the stringer to sit on something, that carries load in compression rather than relying on fasteners in shear.

Blocking behind the connection point spreads the load into the deck frame rather than concentrating it in one board. The deck framing itself has to be capable of taking it, which is one more reason the frame and the stairs get planned together rather than sequentially.

Hardware must suit treated lumber. Hot dip galvanised or stainless, with matching fasteners. Electroplated hardware corrodes in contact with modern treated wood.

At the bottom, stringers should be secured to the landing rather than simply resting on it, using an anchored connector. This resists the stairs sliding out at the base.

The Landing Is Structural

Missing from most stair guides and a genuine requirement.

Stairs need a solid, stable landing at the bottom. Not grass, not bare soil, not a couple of pavers set on dirt.

The requirement is commonly a landing at least as wide as the stairs and at least thirty six inches deep in the direction of travel.

Why it matters structurally. The bottom of the stringers carries load into that surface. Set on soil, the stringers sink, which changes the bottom riser height and breaks the uniformity rule. Soil also holds moisture against the stringer ends, and end grain in contact with wet ground rots quickly.

What works:

• A poured concrete pad on a compacted base
• Pavers or slabs on a properly prepared and compacted base
• Either one sloped very slightly away from the house for drainage

Detail the stringer ends. Cut square, sealed with end cut preservative, and ideally held slightly off the surface by a connector rather than sitting flat in whatever water collects there.

Why the landing elevation must be settled before you calculate. Everything in the rise calculation depends on the finished landing surface height. Build the stairs to the current ground and then pour a pad, and every riser is now wrong.

Handrails Are Required, Not Decorative

A correction worth stating plainly, because handrails are frequently presented as an aesthetic option.

Stairs with four or more risers generally require a handrail. This is a code requirement.

Height is commonly between thirty four and thirty eight inches, measured vertically from the nosing line of the treads.

Graspability is specified. A handrail has to be a shape and size a hand can close around, which is why a wide flat board on top of a guard does not satisfy the requirement on its own. Round profiles within a defined diameter range qualify, as do certain shaped profiles with specified dimensions.

Continuity. The handrail must run the full length of the flight, and the ends need to be returned to a wall or post rather than left projecting, since a projecting end catches clothing and bags.

One side is generally sufficient on residential stairs.

Common failures: a two by four laid flat on top of the guard, a handrail that stops short of the bottom tread, no return at the ends, and height measured from the deck rather than from the nosing line.

This interacts with the guard system, so the two are best chosen together rather than the handrail being added afterward to satisfy an inspector. Different railing systems handle the stair handrail requirement differently, and some need a separate handrail entirely.

Guards and the Openings Rule

Guards and handrails are different things that often occupy the same structure.

Guards prevent falling off the side. They are required where the stairs are above a certain height, and on stairs the guard height is commonly measured from the nosing line, with a lower minimum than on the deck itself.

The openings rules on stairs are specific:

• A four inch sphere generally must not pass through openings in the guard.
• The triangular opening formed by the tread, the riser, and the bottom rail is treated separately, and a larger sphere is commonly permitted there, around six inches.
• Open risers, meaning stairs with a gap where the riser board would be, must not allow a four inch sphere to pass. This limits how open a riser can be relative to the rise height.

Guard posts on stairs face the same load requirement as elsewhere, applied at an angle, and need proper hold down hardware rather than lag bolts through the stringer. Notching a stringer to receive a guard post removes material where the stringer can least afford it.

Lighting. Illumination at stairs is commonly required, and it is a good idea regardless. Riser lights below the tread nosing light the step without shining into anyone's eyes.

Materials, Traction, and Wisconsin Winters

Stairs take more abuse than the rest of the deck and they are where people fall.

Treads take concentrated load. Two by material used for treads is common, and the stringer spacing has to suit it.

Composite treads flex more than wood. Manufacturers usually specify closer stringer spacing for that reason, often twelve inches. This is not optional and it is a common oversight.

Traction matters more here than anywhere else on the deck. Smooth treads are treacherous when wet and worse when frosted. Grooved decking, textured composite, or applied non slip strips all help. Some composite products offer a more textured face specifically for stair use.

Stairs ice first and clear last. They are shaded by the deck above, they are narrow, and they are the least convenient part to shovel. A north facing set of stairs holds ice for weeks after the deck itself is clear.

Snow clearing damages what sits proud. Surface mounted lights and hardware on treads meet shovels. Flush recessed riser lights survive.

Salt and ice melt are used most heavily on stairs, which is where hardware corrosion concentrates. Stainless hardware pays for itself here more than anywhere else on the deck.

Drainage between treads. Gaps between tread boards let water and melt drain rather than sitting on the step and freezing.

Frost Movement at the Bottom of the Stairs

A local consideration that causes uniformity failures a year or two after construction.

The deck is on footings below frost depth. The stair landing usually is not. A concrete pad poured on grade will heave seasonally, which means the bottom of the stairs moves relative to the top.

What that produces. The bottom riser height changes through the year. In a bad case, heave lifts the landing enough to push the stringers up and stress the top connection.

Options:

• Footings under the landing to the same depth as the deck footings, which is the thorough solution
• A floating connection at the base that allows the landing to move without transferring force into the stringers
• A well drained, properly compacted base under the pad, which reduces heave by reducing the water available to freeze

Drainage is the underlying factor. Water that cannot drain away from under the pad is what freezes and lifts. Sloping the grade away and using a free draining base material addresses much of it.

This is worth deciding deliberately rather than by default, because it is the difference between stairs that stay uniform and stairs that develop an odd bottom step in year two.

Inspection and What Gets Checked

Stairs are part of the deck permit and they get inspected.

What an inspector looks at:

• Riser height and tread depth against the limits
• Uniformity across the flight, measured rather than eyeballed
• Stringer size, spacing, and remaining throat depth
• How the stringers are attached at top and bottom
• The landing surface and its dimensions
• Handrail presence, height, graspability, continuity, and returns
• Guard height and the openings rules
• Hardware type and whether fasteners are correctly installed

Stairs are a common failure point, usually on uniformity or on the handrail.

Check it yourself first. Measure every riser and every tread, top and bottom included. Confirm the handrail height from the nosing line rather than from the deck. Confirm the ends are returned.

Understanding the permit and inspection sequence for your municipality avoids the scheduling problems that cost the most, since stairs are usually reviewed as part of the framing or final inspection.

Conclusion

Deck stairs come down to arithmetic done in the right order. Measure the total rise to the finished landing surface, divide by a whole number of risers, and divide back to get the actual rise per step. Treads are always one fewer than risers. Then check both figures against the limits before anything is cut.

The two things that most often go wrong are worth repeating. Every riser in the flight must be within about three eighths of an inch of every other, because your foot learns the rhythm on the first step and stops checking. And the bottom of the stringer has to be cut down by one tread thickness, or the bottom riser ends up taller than all the others by exactly that amount.

Beyond geometry, three items are not optional. Stringers need proper connection hardware at the top rather than fasteners into end grain. Stairs need a solid landing at least as wide as the flight, because stringers sitting on soil sink and rot. And four or more risers means a handrail at a specified height with a graspable profile, which is a safety requirement rather than a design choice.

Get Your Stairs Built Right

If you are working out where stairs should land, whether the geometry works for the height you are dealing with, or how to handle a landing that will not heave, those are quicker to settle on site than on paper. Stairs are also the part of a deck where errors are most expensive to correct after the fact. You can get in touch or call (262) 221-4321.

Serving Milwaukee, Waukesha, Brookfield, Oak Creek, Franklin, Menomonee Falls, and Germantown.

Frequently Asked Questions