Free Guide to Building Stair Stringers

Understanding Stair Stringers: What They Are and Why They Matter

A stair stringer is the structural support system that holds up your stairs. Think of stringers as the backbone of any staircase—they're the angled beams that run diagonally from the bottom step to the top step, and they bear all the weight of both the stairs themselves and anyone walking on them. Most staircases use either two stringers (one on each side) or three stringers (two on the sides and one in the middle), depending on the width of the staircase and how much weight it needs to support.

Understanding how stringers work is essential before you attempt to build them. When you walk up or down stairs, you're putting significant pressure on these structural components. The stringer must be strong enough to handle not just your body weight, but also the weight of the stairs themselves and the repetitive stress of people walking on them over time. Building inadequate stringers can result in sagging, movement, cracking, or even complete failure—situations that create safety hazards and are expensive to repair.

There are three common types of stringers: open stringers, closed stringers, and notched stringers. Open stringers have the treads (the horizontal parts you step on) sitting on top of them, leaving the sides visible—this style is popular in modern homes and gives staircases an airy appearance. Closed stringers have the treads built into the sides or recessed into the stringers themselves, giving a more finished look. Notched stringers, also called cut stringers, have the treads and risers (vertical pieces) notched directly into the stringer material. Each type requires different building methods and materials.

Before you plan your stringer project, you need to know your local building codes. Building codes exist in virtually every municipality in the United States, and they specify how stairs must be built to be safe. Codes typically require specific measurements for step height (called the rise), step depth (called the run), and how much weight stairs must support. These codes are enforced through inspections, and non-compliant stairs can be ordered to be removed or rebuilt. Learning what your local codes require is your first step toward building stringers that are both safe and legal.

Practical Takeaway: Before purchasing any materials, contact your local building department and request information about stair requirements. Ask specifically about required rise and run dimensions, maximum variation between steps, handrail specifications, and whether you need permits for your stringer project. This information will guide all your planning decisions.

Essential Measurements and Calculations for Stringer Layout

Getting your measurements right is the most important part of building stringers. Small errors in measurement multiply as you work, potentially resulting in stairs that don't fit or stairs that are unsafe. The two critical measurements you need are the total rise and the total run. The total rise is the vertical distance from the finished floor at the bottom to the finished floor at the top. The total run is the horizontal distance your stairs will cover.

To measure the total rise accurately, measure from the floor surface where the stairs will start to the floor surface where they will end. Use a long level and a tape measure. Measure in at least three or four different locations if the floors aren't perfectly level, and use the highest measurement—this ensures that at minimum, your shortest step will meet code. Building codes typically specify that risers (the height of each individual step) can vary by no more than 3/8 of an inch between steps in a single staircase. This small variation prevents people from tripping, as their body becomes accustomed to a consistent step height.

Once you know your total rise, you divide it by the height of each individual step to determine how many steps you need. Most building codes require risers between 7 and 7.75 inches tall. However, you should always check your local code, as some jurisdictions allow different measurements. Here's an example: if your total rise is 42 inches and you want 7-inch risers, you would divide 42 by 7, which gives you 6 steps. If you get a number with a remainder—like 45 inches divided by 7 equals 6.43—you need to adjust. You would instead create 7 steps, which means each step would be 45 divided by 7, or about 6.43 inches tall. Then you adjust the stringers so the first step (or last step) is slightly shorter to achieve this measurement.

The total run is calculated similarly. Most codes require the tread depth (the part you step on) to be between 10 and 11 inches. If your stairs have 6 steps and you want 10-inch treads, your total run would be 60 inches (6 steps times 10 inches per step). However, because the last step lands on the upper floor, you actually subtract one tread from this calculation. So 5 treads times 10 inches equals 50 inches of horizontal distance your stringers will span.

When you're designing stringers, there's a useful formula called the "rise plus run rule." Adding the rise and run of each step should total between 17 and 18 inches. For example, a 7-inch rise plus a 10-inch run equals 17 inches, which is in the ideal range. This formula helps create stairs that feel comfortable to walk on, as it naturally matches the way most people climb stairs.

Practical Takeaway: Create a detailed sketch of your staircase showing the total rise, total run, the number of steps, and the individual rise and run of each step. Write down these measurements and double-check them before you buy materials or cut stringers. Many builders recommend calculating measurements twice to catch errors before they become expensive problems.

Materials, Tools, and Safety Equipment You'll Need

Building stringers requires specific materials and tools. The right materials ensure your stringers last for decades, while improper materials can lead to premature failure. The most common material for stringers is dimensional lumber—typically 2x10, 2x12, or 2x14 boards made from pressure-treated wood or solid hardwood. The size you choose depends on how far your stringers must span and how much weight they'll support. A 2x10 can typically span about 8 feet with normal residential loads, while a 2x12 can span about 10 feet. If your stringers need to span more than 12 feet, you may need engineered support or to increase to a larger beam size.

For closed stringers and certain construction styles, you may also use plywood, metal stringers, or concrete stringers depending on your design and what your local code permits. Steel stringers are common in commercial buildings and can be engineered for longer spans. Whatever material you choose, verify that it meets your local building codes and is rated for residential stair use.

Essential tools include a circular saw or miter saw for cutting the stringers, a carpenter's square or speed square for marking angles accurately, a stair gauge (a tool that helps mark the rise and run consistently), and a tape measure. A framing square—a large metal square used in woodworking—is particularly useful for marking stringers. You'll also need a level to ensure your stringers are properly positioned. A drill is helpful for pre-drilling holes if you're using fasteners. For safety, you'll need a dust mask when cutting, as sawdust can irritate your lungs, and safety glasses to protect your eyes from flying debris.

To cut stringers accurately, many builders use a stair gauge, which is a small tool that attaches to a framing square and helps you mark the same rise and run on each step. Some builders mark their first stringer on cardboard or plywood as a template, then use that template to mark the remaining stringers identically. This method ensures all stringers match perfectly.

Personal safety equipment is non-negotiable when building stringers. You'll be working with power tools and handling heavy lumber. Wear safety glasses to protect against sawdust and splinters, steel-toed boots to protect your feet if lumber falls, work gloves to prevent splinters, and a dust mask or respirator if you're doing significant cutting. If you're working at heights, use a proper ladder and follow ladder safety guidelines. Never rush or take shortcuts with safety—stair building involves inherent risks that proper equipment helps minimize.

Practical Takeaway: Before starting your project, purchase or borrow all necessary tools and verify that your materials meet local building codes. Many home improvement stores can provide information about which material sizes are appropriate for your specific staircase dimensions. Test your