7 Step Stair Stringer Dimensions

[Rebecca Donnelly]

The stair calculator calculates stair rise and run, stair angle, stringer length, step height, tread depth, and the number of steps required for a given run of stairs. For convenience and flexibility, this stair stringer calculator comes in two forms: automatic and manual. Click on the [?] icons to determine the best calculator for your stairs.

Adding solid risers to your stairs will not change the results of the Stair Calculator, so long as you properly attach the risers before you add the treads, as shown in the Stairs with Solid Risers and 2x12 Treads diagram below.

Before cutting your stringers, double-check all of your measurements, and carefully plan how you will attach (or not attach) a solid riser at the upper connection point of your stringer. Depending on your design, you may need to adjust the depth of your stringer's top step.

For example, if you are not planning to add a riser to the last rise up to your deck or landing, you may need to subtract the thickness of one riser from the calculated Tread Depth [B] on the top step of the stringers. Using the diagram below, picture the top step without the last riser installed. Without the riser, the last tread would either have a gap on the back side or the nose of the tread would not have the same overhang as the other treads. Consider all of the possibilities before cutting your first stringer.

Stringer - The stringer is the structural part of a set of stairs. They are 2x12s (or larger) material - the uncut portion of the stringer should not be less than 5 inches (127 mm) (see diagrams below). In a set of stairs 36 inches wide, there are typically three stringers (one on each end and one in the middle). The Stringer Length is the tip-to-tip length of the cut stringer. The Stringer Length value is the minimum length of 2x12 material required to lay out the stair stringer.

Total Rise [A] - The Total Rise of a flight of stairs is the vertical rise between the bottom of the first step and the top of the finished landing. The Total Rise [A] should not exceed 151 inches (3835 mm) between landings or floor levels.

Height of First Step [E] - The actual finished height of the first step is the same as the Step Height [F], but when you cut the stair stringer, the First Step Height [E] is always the Step Height [F] minus the Tread Thickness [C].

Treads - The Tread Depth [B] should not be less than 10 inches (254 mm). In a given run of stairs, the Tread Depth [B] should not vary by more than 3/8 inch (9.5 mm). Typically, stair treads are either a single 2x12 or two 2x6s.

Number of Steps (Risers) - The number of risers is not necessarily the same as the Steps on Stringer [D]. If the Stinger Mount Type is Flush, then the number of risers is the same as the number of steps. If the Stringer Mount Type is Standard, the number of risers will be one more than the number of Steps on Stringer [D].

Stairs and Landings - Landings break up long runs of stairs (where the Total Rise [A] is more than 151 inches). The building code further states that the minimum width of a landing should not be less than the width of the flight of stairs served. **"Where the stairway has a straight run, the depth in the direction of travel shall be not less than 36 inches (914 mm)." For additional information, check out Stairs with Landings.

The old Mobile Stair Calculator is available now on mycarpentry.com but will be deprecated soon. I urge you to try the Stair Calculator on this webpage on your mobile or tablet device. You will find its responsive design works as well on mobile devices as on a desktop computer.

Use the Automatic Calculator if the only crucial factor in your stair design is the Total Rise [A]. Using a few (modifiable) default settings, the automatic calculator will compute all of the other factors, including the Total Run [G].

The Total Rise [A] is the finished height of your landing or deck. The TargetStep Height [F], is the height that you would like your steps to be. The automatic calculator will design your stair stringer as close to the target height as possible, while maintaining a common step height. You can also alter the Tread Thickness [C] and Tread Depth [B] as needed. Follow the steps below to design your stair stringer:

Once the stair results have been calculated, you can toggle between the Standardand Flush options to compare the differences. Since the Tread Depth [B] is a constant, when using the Automatic Stair Calculator, the Total Run [G] will vary when you toggle between the two mount options.

Once you determine the Total Rise, Total Run, and Tread Thickness, the most important variable is the Number of Steps. The first time you enter a value in the Number of Steps field, it will likely be a guess. Each time you change the Number of Steps value and recalculate, make note of the Step Height and Tread Depth. If the numbers are too high, add some more steps. Building codes suggest Step Height [F] be no more than 7 3/4" and the Tread Depth [B] be no less than 10".

Once the stair results have been calculated, you can toggle between the Standardand Flush options to compare the results. Unlike the Automatic Calculator, you will notice that the Tread Depth [B] will vary on the Manual Stair Calculator because the Total Run [G] is a constant and the Tread Depth [B] is a variable.

Stair stringers are the diagonal supports that run along the sides of a staircase, providing the framework for treads and risers. Typically cut from 2-by-12 lumber, stringers are notched to create a zigzag pattern that accommodates the steps. They transfer the load of the stairs and people using them to the upper and lower levels of the structure.

Choosing the appropriate material for your stair stringers helps ensure the longevity and safety of your staircase. The right choice depends on various factors, including the location of the stairs and the expected load.

For stairs with landings, treat each flight of stairs as a separate unit with its own stringers. Ensure the landing is level and properly supported and attach the upper and lower stringers to the landing framing securely.

Specialized hardware like the Simpson LSC Adjustable Stringer Connector can simplify attachment and provide additional support. These connectors allow for easy adjustment during installation and provide a strong, code-compliant connection.

You may also want to consider adding a slight slope to exterior treads (about 1/8 inch per foot) to allow water runoff. If you encounter any squeaks after installation, you may need to fix squeaky stairs by reinforcing connections or adding shims.

While many code requirements are standardized, some aspects can vary by region, such as the stringer spacing requirements, the specific materials allowed for exterior use, and any additional requirements for commercial or public staircases. Always check with your local building department for the most up-to-date code requirements in your area.

During a home inspection, the stair stringers are usually covered up, and therefore not observed and not inspected. A home inspection report shall identify, in written format, defects within specific systems and components defined by the Home Inspection Standards of Practice that are both observed and deemed material by the inspector. The home inspection will not reveal every issue that exists or ever could exist, but only those material defects observed by the inspector on the date of the inspection.

Structural performance issues of stair stringers in residential buildings can result in problems ranging from cracking of the cosmetic finish and vibrations to major structural failures, which can result in severe injuries. Despite those issues, there are a lot of general rule-of-thumb recommendations but very few specific prescriptive code construction provisions for wood-framed stair stringers in residential buildings.

Stair stringers should meet the general construction standards except where amended by the local jurisdiction. The International Residential Code (IRC) and the International Building Code (IBC) contain few provisions regarding wood-framed stair stringer design and construction. Most of the code provisions describe dimension minimums and maximums for width, rise, run, and vertical height. There are limited dimensional constraints for residential interior stair construction. Therefore, it's mostly left to the builder's or contractor's knowledge, experience, and the rules-of-thumb they follow in relation to stair stringers.

The stair stringer is a structural member installed on either side or in the center of a flight of stairs into which the treads and risers are attached. The primary function of the stringer is to provide a framework and load-bearing support for the treads and risers.

According to the 2018 IRC, R311.7.5, the riser height maximum is 7-3/4 inches (196 mm). That is measured vertically between the leading edges of the adjacent treads. The tread depth must be at least 10 inches (254 mm). See the illustration above. That is measured horizontally between the vertical planes of the foremost projection of the adjacent treads at a right angle to the tread's leading edge. These tread and riser dimensions directly affect the size of the stringer board, the throat dimensions of a cut stringer, and the amount of board remaining beneath the tread-riser piece that was removed. The throat depth is the net depth of a stringer once the steps are cut and removed, and it is measured from the step perpendicular to the bottom edge of the stringer.

Stairs inside a house are often built by two different contractors. Framers will cut stringers from 2x12-inch boards or sometimes laminated veneer lumber (LVL), and then attach rough treads for temporary use during the home's construction. A finish carpenter will later remove the rough treads and install finished treads, risers, and inner and outer skirt boards. Some finish carpenters prefer to remove the entire rough stairway and build a housed-stringer stairway that has treads and risers fitted and glued into routed dadoes of closed, solid stringers. And the stringers and treads could be made from 5/4-inch- thick boards of pine, poplar, oak, or Douglas fir. The information presented here covers 2x12-inch board stringers.

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