How to Build Stairs — Calculating Rise and Run Guide for Eastern Washington Homeowners & Contractors

Understanding Rise and Run: The Foundation of Safe, Comfortable Stairs

Building stairs that feel natural to climb starts with one critical measurement: the total finished floor-to-finished floor height. This isn’t the rough framing height you might measure during construction, but the actual distance from the completed surface of your lower floor to the completed surface of your upper floor, including all finish materials like hardwood, tile, carpet, or underlayment.

In Eastern Washington, where we experience dramatic temperature swings and freeze-thaw cycles, getting these measurements right from the start prevents costly mistakes down the road. The basic principle is simple: divide your total rise into uniform steps that meet Washington state code requirements while creating a comfortable climbing experience.

Washington’s residential stair code requires riser heights between 4 and 8 inches, with at least 9 inches of tread run. More importantly for comfort, most experienced builders in the Spokane area aim for riser heights around 7 to 7.5 inches, creating stairs that feel natural for most people to use.

The uniformity requirement is non-negotiable: no riser or tread in your stairway can vary more than 3/8 inch from the others in the same flight. This isn’t just about code compliance—even small variations in step height create tripping hazards because people naturally expect each step to match the rhythm they establish climbing the first few steps.

For exterior stairs serving homes from Airway Heights to Colville and Kettle Falls, these calculations become even more critical. Snow loads, ice formation, and the expansion and contraction that comes with our hot summers and cold winters mean your stair geometry needs to be precisely planned and built with materials that won’t shift or settle unevenly.

Step-by-Step Calculation Process

Measuring Total Rise Accurately

Start by measuring the vertical distance from your finished lower floor to your finished upper floor. If you’re building before finish floors are installed, you’ll need to add the thickness of both floor coverings to your rough measurement. A common mistake is forgetting that your bottom step might sit on a concrete slab with tile, while your top step meets a wood subfloor with hardwood and underlayment—that’s potentially a 1.5-inch difference that will throw off your first or last riser height.

Use a long level or laser level to get an accurate vertical measurement, especially if your floors aren’t perfectly level. In older homes throughout Eastern Washington, settling and seasonal movement often mean floors are slightly out of level. Account for this early rather than discovering the problem after your stringers are cut.

Determining Number of Steps

Divide your total rise by your target riser height to get the number of steps. If your total rise is 96 inches and you want 7-inch risers, you get 13.7 steps—which means you need 14 risers. Now divide 96 by 14 to get your actual riser height: 6.86 inches, which rounds to about 6⅞ inches per step.

This process of adjusting ensures all your risers are identical. Many builders create a story pole—a long board marked with each riser height—to verify the layout before cutting stringers. This simple step prevents the accumulation of small errors that can leave you with one dramatically different step height.

Calculating Tread Run

Washington requires at least 9 inches of tread run, but most builders in our climate zone prefer 10 to 11 inches for comfort and safety. Wider treads provide better footing, especially important when stairs might be wet from snow tracked in on boots or morning frost on exterior steps.

Remember that if you have 14 risers, you’ll have 13 treads—the top “step” is actually your upper floor surface. Calculate your total horizontal space by multiplying tread count by tread depth, then add space for any landings and the thickness of your bottom and top framing.

Eastern Washington Climate Considerations

Seasonal Movement and Material Selection

Our region’s temperature extremes create unique challenges for stair construction. Summer temperatures regularly reach the 90s while winter lows drop well below freezing. This 100-degree-plus swing causes significant expansion and contraction in building materials, particularly lumber.

Choose stringer material carefully. Many experienced contractors in the Spokane area prefer laminated veneer lumber (LVL) for stringers because it’s more dimensionally stable than solid lumber and won’t twist or bow as much with seasonal changes. If using solid lumber, make sure it’s properly dried and acclimated to your building’s conditions before installation.

For exterior stairs, pressure-treated lumber is essential, but pay attention to the treatment type and drying level. Wet treated lumber can shrink significantly as it dries, potentially affecting your carefully calculated rise and run measurements.

Drainage and Ice Management

Exterior stairs in Eastern Washington must shed water quickly to prevent ice formation and freeze-damage. This affects your tread design and pitch calculations. Plan for a slight forward slope on treads—about 1/8 inch per foot—to encourage water runoff while maintaining safe footing.

Consider tread materials that provide good traction when wet or icy. Composite decking materials often work better than smooth lumber for exterior applications, and anti-slip strips or grooved surfaces can prevent dangerous falls during our icy winters.

Foundation and Footing Requirements

Frost depth in Eastern Washington typically extends 24 to 36 inches below grade, depending on your specific location and exposure. Stair footings must extend below this frost line to prevent heaving that would throw off your rise and run calculations after the first freeze-thaw cycle.

Plan your footing layout early in the design process. The bottom of your stringers needs solid, level support that won’t move seasonally. Concrete pads, properly sized footings, or connection to existing frost-protected foundations are essential for long-term stair stability.

Code Compliance and Safety Requirements

Headroom and Clearance

Washington requires minimum 6 feet 8 inches of headroom measured vertically from the tread nosing to the ceiling or structure above. Check this measurement at several points along your stair run, not just at the top and bottom. A common mistake is failing to account for floor joists, ductwork, or sloped ceilings that might create headroom problems in the middle of the stair run.

If you’re working with tight headroom conditions—common in basement stairs or loft conversions—you might need to adjust your stair pitch or create a landing to maintain code compliance. This is where professional help often pays for itself, as experienced builders know how to maximize headroom within structural constraints.

Handrail and Guard Requirements

Stairs require at least one handrail, and guardrails are required where there’s a drop-off hazard. Handrails must be between 34 and 38 inches above the tread nosing, with specific requirements for grip size and clearance from walls.

Guard openings cannot allow a 4-inch sphere to pass through, which affects baluster spacing calculations. In Eastern Washington’s climate, choose handrail materials that won’t become dangerously slippery when wet or when handled with gloves during winter months.

Common Mistakes and How to Avoid Them

The most expensive stair-building mistake is measuring incorrectly at the start. Using rough framing heights instead of finished floor heights leads to that one step that’s noticeably different from all the others—a safety hazard and a constant reminder of the error.

Another frequent problem is not accounting for out-of-level conditions. If your lower floor slopes 1/2 inch across the width of your stair, and you don’t adjust for this, your stringers won’t sit properly and your handrail installation becomes much more complicated.

Cutting stringers without using a template after perfecting the first one leads to small variations between stringers that create an uneven, unprofessional feel. Take time to get the first stringer perfect, then use it as a template for all subsequent stringers.

For exterior stairs, underestimating drainage requirements causes long-term problems. Water that can’t escape freezes, expands, and damages your carefully built structure. Design your stairs like a roof—everything should shed water away from the structure quickly and completely.

Skipping the permit review process can lead to expensive rebuilds. While simple interior stairs might not require permits in all jurisdictions, exterior stairs, stairs with structural changes, and stairs in remodel projects often do. Check with your local building department before cutting lumber.

Material Selection for Eastern Washington Conditions

Lumber and Engineered Products

For stringers, dimensional lumber remains popular, but choose carefully. Look for straight, dry material without large knots in stress areas. Southern pine and Douglas fir both work well in our climate when properly dried. LVL stringers cost more initially but often save money over time due to their stability and precision.

Tread and riser material depends on your finish goals and budget. For painted stairs, 3/4-inch plywood sub-treads and risers work well under finish materials. For natural wood stairs, choose species that handle humidity changes well—oak remains popular for its durability and appearance.

Hardware and Fasteners

Use corrosion-resistant fasteners throughout, especially for exterior applications. Stainless steel or hot-dipped galvanized screws and bolts resist rust in our wet winters and won’t stain wood surfaces over time.

Construction adhesive between treads and stringers significantly reduces squeaks and improves stiffness. Choose adhesives rated for your temperature range—some products don’t cure properly in cold weather or become brittle at low temperatures.

For structural connections, consider engineered connectors designed specifically for stair applications. These provide stronger, more reliable connections than field-fabricated brackets and often simplify installation.

Exterior-Specific Materials

Exterior stairs need materials that can handle UV exposure, moisture, freeze-thaw cycles, and significant temperature swings. Pressure-treated lumber for structure, composite or naturally rot-resistant materials for treads, and stainless steel hardware for connections provide the best long-term performance.

Consider the maintenance requirements of your material choices. Natural wood stairs look beautiful initially but require regular staining or sealing to maintain performance in our climate. Composite materials cost more upfront but often require less maintenance over their lifespan.

Whether you’re planning a simple interior stair for a new addition or a complex exterior stair system for a hillside home, getting the rise and run calculations right from the start determines the success of your entire project. Take time to measure accurately, account for all finish materials, and plan for our region’s specific climate challenges.

At Builders Supply & Home Center, we stock all the materials you need for successful stair construction, from precision-cut stringers and engineered lumber to specialty hardware and composite tread materials. Our experienced staff at our Airway Heights, Colville, and Kettle Falls locations can help you select the right materials for your specific project and local conditions. Visit our online catalog at https://bldrsupply.epicor-inet.com/departments to explore our full range of stair-building supplies and materials.