How to Build Stairs: The Art and Science of Creating Safe, Beautiful Steps

Building stairs is one of those projects that separates weekend warriors from serious builders. I've been constructing stairs for over two decades, and I still remember the anxiety of cutting my first stringer. That fear wasn't misplaced – stairs are unforgiving. Get the math wrong, and you'll know it every time someone trips on that one step that's a quarter-inch off.

The truth about stair building is that it's equal parts mathematics and craftsmanship. You can nail the calculations perfectly, but if your execution is sloppy, you'll end up with stairs that feel wrong underfoot. And trust me, people notice. They might not consciously realize why your stairs feel awkward, but their bodies know.

Understanding the Anatomy of Stairs

Before you pick up a saw, you need to understand what makes stairs work. The key players are stringers (those zigzag boards that support everything), treads (what you step on), and risers (the vertical bits between treads). Simple enough, right? Well, here's where it gets interesting.

Stringers are the backbone of your stairs. I've seen too many DIYers try to save money by using 2x10s when they really needed 2x12s. The result? Bouncy stairs that feel like they're about to collapse. Your stringers need to be beefy enough to handle not just normal foot traffic, but also that time when three people are carrying a couch up the stairs.

The relationship between tread depth and riser height is sacred. There's an old formula that carpenters have used for centuries: two risers plus one tread should equal 24 to 25 inches. Why? Because that's how human legs work. Mess with this ratio, and you'll create stairs that tire people out or cause them to stumble.

The Mathematics Behind Safe Stairs

Let me share something that took me years to fully appreciate: stair math isn't just about making things fit. It's about creating a rhythm that human bodies expect. When we walk up stairs, our brains anticipate each step based on the previous one. Break that pattern, and you break ankles.

Start with your total rise – the vertical distance from the bottom floor to the top. Let's say you've got 108 inches. Now, building codes typically allow risers between 4 and 7¾ inches, but I'll tell you a secret: aim for 7 to 7½ inches. It's the sweet spot that feels natural to most people.

Divide your total rise by your target riser height. In our example, 108 inches divided by 7.5 inches gives us 14.4. Since you can't have 0.4 of a step, you'll need either 14 or 15 risers. Choose 15, and your actual riser height becomes 7.2 inches (108 ÷ 15).

Now for the treads. Building codes usually require a minimum of 10 inches, but 11 inches feels more generous. With 15 risers, you'll have 14 treads (you always have one less tread than risers – think about it, the top floor acts as your final tread).

Cutting Your First Stringer

This is where the rubber meets the road. Or rather, where the saw meets the wood. I still use a framing square for laying out stringers, despite all the fancy stair gauges on the market. There's something satisfying about the old-school method that connects you to generations of carpenters.

Clamp stair gauges to your framing square at your rise and run measurements. Place the square on your 2x12, with the rise measurement on the tongue and the run on the blade. Mark your first step, slide the square along, and repeat. It's meditative work that requires precision.

Here's a tip that'll save you heartache: cut your first stringer completely, then use it as a template for the others. But before you cut the rest, test fit that first stringer. I learned this lesson the hard way when I cut three stringers only to discover I'd misread my measurements. That was an expensive mistake.

When you're cutting with a circular saw, don't cut all the way to the corner – you'll weaken the stringer. Stop just short and finish with a handsaw. Yes, it takes longer. No, you can't skip this step if you want stairs that last.

The Installation Dance

Installing stairs is like a carefully choreographed dance. You can't just slap them in place and hope for the best. Start by securing your stringers to the header at the top. Use joist hangers – don't just toenail them and call it good. I've seen too many stairs pull away from headers because someone wanted to save ten bucks on hardware.

At the bottom, your stringers need solid bearing. If you're on concrete, use treated lumber for a kick plate and anchor it with concrete screws. On wood floors, make sure you're hitting joists, not just subfloor. Stairs carry tremendous loads, especially when people are moving furniture.

Level is crucial, but here's something most guides won't tell you: perfectly level stringers can still result in wonky stairs if your floors aren't level. Sometimes you need to compromise, creating stairs that feel right even if they're not technically perfect. This is where experience trumps theory.

Treads, Risers, and the Finishing Touches

I prefer to install risers first, then treads. It's not the only way, but it gives you more room for adjustment. Use construction adhesive in addition to screws – squeaky stairs are the bane of midnight snack runs.

For treads, hardwood is classic, but don't overlook other options. I've used everything from reclaimed barn wood to steel plate. The key is consistency. Whatever material you choose, every tread should feel the same underfoot. Mix materials at your peril.

Nosing – that little overhang at the front of each tread – isn't just decorative. It gives your foot a bit more purchase and makes the stairs feel more substantial. An inch to an inch and a quarter is ideal. Less feels stingy; more becomes a tripping hazard.

Building Codes and Common Sense

Building codes exist for good reasons, usually written in someone's blood. But codes are minimums, not targets. Just because code allows a 7¾-inch riser doesn't mean you should build them that tall. I've found that staying well within code requirements results in stairs that feel better and last longer.

Handrails are non-negotiable for me, even when code doesn't require them. I've installed them in three-step entrances where code said they weren't necessary, and homeowners always thank me later. As we age, those handrails go from convenience to necessity.

The 4-inch sphere rule – no opening should allow a 4-inch sphere to pass through – seems arbitrary until you realize it's about the size of a toddler's head. Suddenly, that boring building code becomes very real.

Outdoor Stairs: A Different Beast

Exterior stairs face challenges that indoor stairs never see. Water is the enemy. Every joint, every connection point, every surface is a potential failure point when water gets involved. I've torn out more rotten exterior stairs than I care to remember, usually because someone tried to build them like interior stairs.

Use pressure-treated lumber for stringers, even if you're planning to cover them. Slope your treads slightly – about 1/8 inch per foot – to encourage water runoff. And for the love of all that's holy, use appropriate fasteners. Those cheap zinc-plated screws will rust out in a few years, leaving you with wobbly, dangerous stairs.

Consider composite decking for treads. Yes, it's more expensive than wood, but it won't rot, splinter, or need annual staining. In my experience, the extra upfront cost pays for itself in reduced maintenance and longer life.

The Spiral Staircase Temptation

Every few years, a client asks about spiral stairs. They've seen them in magazines, looking all architectural and space-saving. Here's my take: unless you absolutely need them due to space constraints, avoid them. They're difficult to build correctly, harder to navigate (especially with furniture), and often don't meet code for primary stairs.

If you must have spirals, buy a kit from a reputable manufacturer. This isn't the place to experiment with your carpentry skills. I've installed several spiral stair kits, and even with clear instructions, they're challenging. The tolerances are tight, and mistakes compound quickly.

Mistakes That Haunt Me

Let me share some failures that taught me valuable lessons. Early in my career, I built a set of basement stairs with inconsistent risers. The homeowner had changed the floor plan mid-project, and I adjusted the bottom riser to accommodate. Just one inch difference, but people tripped on those stairs constantly. I ended up rebuilding them for free – an expensive lesson in the importance of consistency.

Another time, I trusted old plans without verifying measurements. The stairs I built were perfect – for the ceiling height shown on the plans. Too bad the actual ceiling was six inches lower. Always measure twice, cut once, and verify everything yourself.

The Satisfaction of Well-Built Stairs

There's something deeply satisfying about building stairs that will outlast you. Every time I walk on a set of stairs I built twenty years ago, still solid and squeak-free, I feel a connection to the long tradition of builders who understood that some things are worth doing right.

Good stairs disappear into the background of daily life. People use them thousands of times without thinking about them. That's the goal – stairs so well-proportioned and solidly built that they become invisible. It's only when stairs are wrong that people notice them.

Building stairs isn't just about connecting two floors. It's about understanding human movement, respecting the materials, and taking pride in creating something that serves a fundamental need. Whether you're building a simple basement stair or an elaborate main staircase, the principles remain the same: measure carefully, cut precisely, and never compromise on safety.

The next time you walk up a flight of stairs, pay attention to how they feel. Notice the rhythm of your steps, the solidity underfoot, the confidence you have in each tread. That's what you're aiming for when you build stairs – that unconscious trust that each step will be where your foot expects it to be.

Authoritative Sources:

Burrough, R. Stairbuilding and the Steel Square. Sterling Publishing, 2003.

Love, T.W. Basic Stairbuilding. The Taunton Press, 1999.

Schuttner, Scott. Basic Stairbuilding. Fine Homebuilding, 2010.

U.S. Department of Housing and Urban Development. Residential Rehabilitation Inspection Guide. HUD User, 2000.

International Code Council. International Residential Code. ICC, 2021.