Learn How to Build Stair Stringers Yourself

Understanding Stair Stringers and Their Purpose

A stair stringer is the diagonal support beam that holds up the steps of a staircase. Think of it as the backbone of your stairs. When you look at stairs from the side, you see a zigzag pattern—that's the stringer. Most residential staircases use either one, two, or three stringers depending on the width of the stairs and how much weight they need to support.

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Stringers come in two main types: cut stringers and routed stringers. A cut stringer is made by cutting notches into a board to create the step support. A routed stringer uses a different method where the board is shaped with a router tool. For a DIY builder, cut stringers are typically easier to construct because they require basic carpentry tools and straightforward measurements.

Building your own stringers saves money compared to purchasing pre-made ones, which can cost $150 to $400 per stringer depending on the staircase design. The National Association of Home Builders reports that labor costs for stair installation make up a significant portion of total staircase expenses. By building stringers yourself, you control the cost of materials while developing practical carpentry skills.

The stringer supports all the weight of the staircase—including the treads (the horizontal parts you step on), risers (the vertical parts between steps), and anyone using the stairs. Building Code requires stringers to handle substantial weight loads. Understanding how stringers work helps you build stairs that are both safe and long-lasting. Before starting your project, check your local building codes because stair construction requirements vary by location.

Practical Takeaway: Measure the total vertical height and horizontal distance of where your stairs will go. These two measurements form the basis for all stringer calculations and determine what size board material you'll need.

Gathering Materials and Tools for Stringer Construction

The main material for a residential stringer is lumber, typically 2×12 boards. A 2×12 provides enough thickness and width to safely support stair weight. You'll want to select lumber that is straight and free from warping, knots, or damage. Check the board by sighting down its length—if you see bows or twists, choose a different board. Most home improvement stores sell 2×12 boards in lengths up to 20 feet, which is sufficient for residential stairs.

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For a typical basement staircase going down 10 feet with 7-inch steps, you'll need one or two 2×12 boards depending on staircase width. Calculate the total linear distance of your stringer by using the Pythagorean theorem: square root of (rise squared plus run squared). For example, if your total rise is 10 feet and total run is 9 feet, your stringer length would be about 13.5 feet. Purchase boards about 2 feet longer than calculated to allow for cutting and adjustments.

Essential tools for building stringers include a circular saw or miter saw, a carpenter's square (also called a speed square), a tape measure, a pencil, and a carpenter's level. A stair gauge or framing square makes layout much easier and reduces errors. You'll also need a handsaw or oscillating multi-tool for finishing cuts. Safety equipment is critical: wear safety glasses, hearing protection, and dust masks when cutting lumber. A work surface like a sturdy sawhorse setup keeps your board stable while you work.

Additional supplies include sandpaper (80-grit and 120-grit) for smoothing edges, wood filler if you make mistakes in your cuts, and wood stain or sealant if you want a finished appearance. Pre-drill holes if you'll be attaching stringers with bolts or lag screws to prevent splitting the wood. A carpenter's pencil marks clearly on wood better than regular pencils.

Practical Takeaway: Visit your local building supply store and examine 2×12 boards in person. Pick boards that feel straight, look free of damage, and have consistent color and grain. Ask staff about bulk pricing if buying multiple stringers.

Measuring and Calculating Rise and Run

Rise and run are the two most important measurements in stair building. Rise is the vertical distance you need to climb, while run is the horizontal distance covered by the steps. Professional carpenters use the formula: rise per step should be 7 to 7.75 inches, and run per step (tread depth) should be 10 to 10.25 inches. These measurements come from building codes based on how people naturally climb stairs safely.

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Start by measuring the total vertical distance from the bottom floor to the top floor. Use a long level and a tape measure. Measure at multiple points because floors aren't always perfectly level. Use the lowest point as your total rise measurement. Let's say your total rise is 9 feet 3 inches (111 inches). Divide 111 by 7.5 (the ideal rise per step) and you get approximately 14.8 steps. Round to 15 steps. Now divide 111 inches by 15 steps, giving you 7.4 inches per step—well within code.

Next, measure the horizontal distance available for your stairs. This is your total run. If you have space for 14 horizontal feet of stairs, that's 168 inches total run. Divide 168 inches by 15 steps (from our previous calculation) and you get 11.2 inches per step. This is slightly more than the standard 10.25 inches, but still acceptable and makes for comfortable stairs.

Building Code across most U.S. states specifies that the rise variation between steps cannot exceed 3/8 inch (0.375 inches). This means every step must be almost exactly the same height. If you calculate 7.4 inches per step, every single step should measure between 7.1 and 7.7 inches—not more. This consistency prevents tripping hazards. Record all your measurements on paper before touching any tools. Double-check calculations by adding them: (15 steps × 7.4 inches rise) should equal your original 111-inch total rise.

Practical Takeaway: Write your rise and run measurements on a piece of tape and stick it to your stringer board. Include both the total measurements and the per-step measurements. This prevents calculation errors while you're making cuts.

Laying Out and Marking Stringer Cuts

With your measurements finalized, the next step is marking your board accurately. This is where most DIY mistakes happen, so take your time. Start with your 2×12 board laid flat on sawhorses, and ensure it's secure and won't move while you work. Set a carpenter's framing square or stair gauge on the board at the angle that matches your rise and run. If using a regular framing square, the rise measurement goes on one leg and the run measurement on the other leg.

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Most framers use a tool called a stair gauge, which clamps onto a framing square and helps position it identically for each step. If you don't have a stair gauge, tape measures clamped to the framing square work well. Position the square so the rise measurement (7.4 inches in our example) aligns with the left edge of the board and the run measurement (11.2 inches) aligns with the top edge. This creates the proper step angle.

Trace along the square's edges with a sharp pencil. Then slide the square down the board so the previous line's end becomes the new starting point. This stair-step pattern continues down the length of the board. For 15 steps, you'll make 15 triangular marks. At the bottom of the board, you'll have a partial mark that becomes your final step's cut. At the top, you typically cut off a portion to create a level surface where the stringers attach to the upper floor or landing.

Mark a line along the back (or side) of the stringer showing where the stringers will be supported. This line indicates the bearing surface and helps ensure your stringers sit properly on their support. Use a level to verify your marks are accurate before cutting. Sight down the board from multiple angles to catch any pencil-marking mistakes. Some builders create a cardboard template first, testing it against a mock-up of their stairs before committing to cuts on expensive lumber.

Practical Takeaway: Make all your marks in pencil first. Step back