What Is a Stair Stringer and How Does It Work?

What Is a Stair Stringer?

A stair stringer supports the treads and risers of a stairway, running along each side or through the center to form the backbone of the staircase. It anchors each step in place and ensures the structure functions safely and reliably.

Builders fabricate stringers from regular steel, stainless steel, or aluminum—depending on the project’s setting and design. Whether in residential or commercial construction, properly installed stringer systems play a critical role in meeting code requirements and keeping users safe.

Why Stair Stringers Matter

A staircase may look simple from the outside, but it is the structure underneath that is doing the heavy lifting.

Stair stringers and other structural components:

• Support the weight of foot traffic and the stair frame itself
• Ensure even spacing and angle for a comfortable and safe ascent or descent
• Maintain structural integrity over time
• Play a key visual role in exposed or open stairway designs
• Vary in size and placement to suit different site requirements

Understanding the role of stair stringers helps contractors and homeowners make informed decisions about design, materials, budget, and building code compliance throughout the planning process.

Types of Stair Stringers

When designing or building a staircase, it’s important to select the right type of stringer system for the job and the aesthetic. Here are the most common types of stair stringers used in construction:

1. Closed (Housed) Stringers

Closed stringers are the most traditional type and conceal the edges of the treads and risers. Often used in finished staircases, these stringers provide a clean, classic look and are commonly found in residential interiors.

2. Open (Cut) Stringers

Open stringers have visible, notched profiles and support the treads from beneath. They’re often used in modern or exterior stairways where aesthetics are less of a concern, or where visibility of the treads is desired.

3. Mono Stringers

This design features a single central support beam—typically made of steel or another metal—running up the center of the stairs. Mono stringer stairs are a sleek and modern option, ideal for floating staircases or open-concept interiors.

4. Double Stringers

Double stringers are placed on either side of the stairs and can be used in both traditional and modern designs. They offer strong support while still allowing for creative railing or tread designs.

Each type offers unique structural and aesthetic advantages. Casco & Sons works closely with contractors and owners alike to design and build the right stringer system for every project.

Stair Stringer Brackets and Attachments

A properly installed stair stringer assembly relies on solid attachment methods and high-quality brackets. These ensure the structure can handle daily use without shifting, sagging, or failing.

Common Types of Stair Stringer Brackets:

• Angle brackets – Secure the stringer to the landing or deck
• Hangers – Provide strong support at the top of the stringer, especially in deck stairs
• Flush-mount brackets – Allow for clean-looking installations

These components are often made from galvanized steel or stainless steel to withstand moisture and corrosion—especially important for outdoor use. Most are custom built to fit particular site conditions and fit requirements, especially in tight spaces.

How Do You Attach Stair Stringers?

Knowing how to attach stair stringers correctly is crucial to a successful and safe installation. While methods vary slightly depending on the project (indoor, outdoor, or steel stairs), the general method is as follows:

1. Measure and Design – Carefully measure the total rise and run of the steps to cut stringers to the correct dimensions and slope. Verify the location and status of the stairway anchor points.
2. Prepare Landing Points – Determine how the top and bottom of the stair stringers will attach—this could be a deck, concrete pad, or floor. These attachment points may need extra attention such as leveling or reinforcing. Footings may be poured separately to ensure stability.
3. Rig and Set the Stairs – Properly rig, hoist, and secure stair components during placement. Ensure installers remain aware of surroundings, and handle all transport with careful communication.
4. Anchor the Top  – Use a stair stringer bracket that’s large enough and thick enough to accommodate the correct type and number of fasteners to secure the stringer to the top support, typically with lag screws in wood, or anchor bolts for concrete.
5. Secure the Bottom – Anchor the bottom of the stringer to the ground or base with approved fasteners to avoid shifting. When measured correctly, the bottom of the stairs should line up comfortably at the midpoint of the footing, if applicable.
6. Install Treads and Risers – Once the stringer is stable and level, attach the treads and risers. Depending on the location, treads may need to be covered to protect them from ongoing construction.
7. Finish with Inspection and Touch Ups – Inspect all bolts for tightness, verify any coating touch-ups, and confirm final installation meets applicable code requirements and project specifications.

For commercial projects or industrial staircases, it’s always recommended to work with a professional like Casco & Sons to comply with applicable building codes, fulfill project specifications, and accommodate site conditions to properly design and build a new stairway.

Common Mistakes to Avoid with Stair Stringers

• Improper measurements for floor to floor that throw off the rise/run ratio and create a code compliance issue resulting in fines and rebuilds
• Using the wrong type of bracket or fastener for structural support and stability, causing delays and/or safety hazards
• Failing to account for deflection or movement, especially in outdoor stairways, or very minimal, modern stair designs with long, unsupported spans
• Not maintaining the original coating or selecting the wrong type for site conditions
• Skipping code requirements, which could result in liabilities due to health and safety violations

Installing stair stringers can involve using a heavy machinery to set a fully welded stair frame or carefully assembling components onsite. Successful installation requires attention to detail, proper planning, and the flexibility to adapt if conditions change. Casco & Sons approaches every project with these priorities in mind.

When to Replace a Stair Stringer

Over time, even well-built stair stringer assemblies can degrade—especially in high-traffic or outdoor environments.

Watch for:

• Visible cracks or splitting wood
• Rust or corrosion on metal stringers
• Sagging stairs or soft treads
• Squeaking or movement when stepped on

If you notice these signs, it’s time to inspect your stringer and consider replacement. Casco & Sons handles professional assessment and recommendations for repairs or replacements, and how to protect your new stairs.

Ready to Build Stronger, Safer Stairs?

At Casco & Sons, we understand that every great commercial staircase starts with a solid foundation—and that begins with expertly crafted and properly installed stair stringer systems. Whether you’re building new stairs, upgrading existing stair framing, or need help with stair stringer services and maintenance, our experienced team is here to help.

From measure to install, we focus on what matters—precision, durability, and safety. Our team works closely with clients during planning and design to keep projects on track and eliminate surprises. Whether for residential or commercial projects, we’re committed to building stair systems that are safe, code-compliant, and built to stand the test of time.

Ready to get started? Contact Casco & Sons today to schedule a consultation or request a quote. Let’s build stairs that last—together.