How to Cut Stair Stringers: A Practical Guide
When it comes to building a safe, functional staircase—whether for a deck, basement, or interior renovation—cutting stair stringers is one of the most critical steps. Stair stringers are the backbone of any staircase, literally and structurally. They support each stair tread and riser, transferring weight and impact down into the floor or foundation. For example, deck stairs rely on properly cut stringers to ensure stability and safety outdoors.
Whether you’re a seasoned professional or a hands-on homeowner tackling your first staircase, cutting stair stringers accurately ensures a secure and long-lasting build. There are several ways to build stairs, including using traditional stringers, open riser designs, or box stair methods, each offering different benefits and aesthetics. This guide walks you through the process, from layout to cutting, offering insights that apply on the job site or in your own backyard.
What are stair stringers?
Before getting into tools and techniques, it’s worth clarifying what we mean by a “stair stringer.” A stringer is the diagonal board that supports the steps of a staircase. Most residential staircases use two or three stringers depending on the width of the staircase and the expected load. The typical material is a 2×12 piece of lumber, chosen for its strength and width, which allows for proper notch depth without compromising structural integrity.
There are two primary types:
- Closed stringers, where the treads and risers fit into grooves cut into the stringer.
- Open stringers, which are notched to visibly support each tread and riser from underneath—this is the type we’ll focus on in this article.
Cutting stair stringers, step by step
Cutting stair stringers might seem complex, but it’s a straightforward process when broken down into clear steps. When cutting stringers, precision is crucial—common mistakes like inaccurate measurements or improper techniques can lead to poor fit and compromise safety. Here’s how to go from measurements to finished cuts with accuracy and confidence.
Step 1: know your stair code
Before making a single cut, review your local building codes. Ensuring building code compliance is crucial for both safety and legality when constructing or renovating stairs. Most codes in the U.S. follow the International Residential Code (IRC), which generally requires:
- A maximum riser height of 7 ¾ inches
- A minimum tread depth of 10 inches
- A minimum stair width of 36 inches
These measurements exist for good reason: safety and comfort. Complying with code ensures your stairs are easy to use and safe for everyone, from toddlers to grandparents. Code compliance is also essential for passing inspections and ensuring long-term safety.
Step 2: do the math
Cutting stair stringers isn’t guesswork, it’s geometry. Start by determining two measurements:
- Total rise (also called overall rise): The vertical height from the finished lower level to the finished upper level.
- Total run: The horizontal length your staircase will span once finished.
Once you have the total rise, divide it by your desired riser height. The result tells you how many steps you’ll need. Let’s say your total rise is 96 inches. Divide that by 7.5 (a typical riser height) and you get 12.8. Round down to 12 risers, then divide 96 by 12 again to get an actual riser height of 8 inches.
For the tread, you’ll use a consistent depth like 10 inches. Multiply that by the number of treads (which is always one less than the number of risers) to get your total run.
Step 3: lay out the stringer
This is where the framing square comes into play. You’ll need:
- A framing square
- Stair gauges (small metal clamps)
- A sharp pencil
- A 2×12 board (the stringer)
- Stair treads (the horizontal surfaces you’ll step on)
Attach your stair gauges to the framing square—one set for the rise, and one for the run. Let’s say you’ve determined an 8-inch rise and a 10-inch run. Clamp the stair gauges at those points on your square. Place the square on the board and trace your first step. Slide the square along the board to repeat the pattern, marking each step and the stair treads precisely.
Remember to account for the thickness of the tread material. If you’re using 1-inch thick treads, subtract that from the bottom of your stringer so the first step isn’t taller than the others. Properly measuring the bottom riser is crucial to ensure the staircase sits flush with the floor and provides stable support. Similarly, the top of the stringer will often be notched or cut at an angle to sit flush with the deck or landing.
Step 4: cut carefully
Use a circular saw to cut along the lines of your layout. Be careful not to cut past the inside corners of each notch. Doing so weakens the stringer and may lead to cracking over time. Instead, stop the saw just short of the corner and finish the cut with a handsaw or jigsaw for cleaner, stronger corners.
After cutting one stringer, use it as a template for any additional ones. When cutting the second piece, carefully align it with the first to ensure a proper fit and support. This ensures consistency across all supports.
Step 5: cutting additional stringers
Once you’ve successfully cut your first stringer, it’s time to create the remaining stringers needed to provide adequate support for the entire staircase. Lay the first stringer on top of a new piece of pressure-treated lumber, such as southern yellow pine or douglas fir, and trace the outline carefully. Using a circular saw, follow the marked lines to cut each additional stringer, ensuring every cut matches the original template.
For extra accuracy, stair gauges or a stringer template can help guide your saw and keep your cuts consistent. Always double check your measurements before making each cut—small errors can add up and affect the stability of your stairs. Using high-quality, pressure-treated lumber will help your stringers resist rot and provide long-lasting support for your staircase, whether it’s indoors or exposed to the elements.
Step 6: test fit and install
Before installing the stringers, do a dry fit to ensure the rise and run work correctly in the space. Double-check the level at both the top and bottom of the stringer. Adjustments might be needed if the ground isn’t perfectly level or if your landing is slightly off. For staircases with landings, each flight may require their own stringers to ensure proper support and stability.
Once everything lines up, you can install the stringers using galvanized hangers or direct framing connections, depending on your structure. Secure the treads and risers afterward, making sure everything is square and flush.
Common mistakes to avoid when cutting stair stringers
- Ignoring lumber quality: Warped or knotted boards can compromise strength and make layout frustrating.
- Forgetting tread thickness: This can throw off the entire stair height.
- Cutting into the board too deeply: Never notch more than a third of the stringer’s width.
- Not planning for finish flooring: If you’re adding tile or another layer, factor that into your total rise.
Cutting stair stringers may seem intimidating, but with careful planning, accurate measurements, and the right tools, it’s a manageable task for any skilled DIYer—and a routine job for professionals.
If you’re taking on a staircase project and need expert advice, durable materials, or professional help, don’t hesitate to reach out to First Atlanta Flooring. We’re here to support every step of your renovation journey.
