How Do You Measure For Basement Stair Stringers?

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Stair stringers are essential when constructing a basement staircase. Without them, you might compromise the safety and function of the stairs. But you may be wondering how to properly get their measurements for your basement. We have done thorough research to give you the answer.

To measure for basement stair stringers, follow these steps:

  1. Measure the "rise" of the staircase.
  2. Decide the height you want for each stair step.
  3. Afterward, divide the total staircase height by the rise of the step. The value you get is the number of steps needed.
  4. Then, divide the stair height with the calculated steps.
  5. Multiply the value from the step above by the desired width to get the "run" of the stairs.
  6. Use the Pythagorean formula to get the length of the stringers.

With the correct measurements, you can create a sturdy basement staircase. You will also decide on the number of stringers, lumber size, and type of material. Read along to know more about basement stair stringers.

A wood stair stringer block at the construction site, How Do You Measure For Basement Stair Stringers?

Getting The Right Basement Stair Stringer Length

You have to comply with implemented residential codes when you decide to put up a basement stairway. A vital component of a staircase is the stair stringer. According to the International Association of Home Inspectors, stair stringers are the vertical supports of the stair risers and treads. With stringers, you create the framework of the stairs.

Wooden stringers and stair banisters leading to the second floor

If you are doing this project on your own, refer to this procedure on how to measure stair stringers:

  1. Get the vertical "rise" of the staircase.
  2. Measure the height for each stair step. A good range will be around 7 to 7.50 inches. It is best to follow the average to avoid accidents on the stairs.
  3. Divide the total staircase height by the rise of the step. You will get the number of steps for the staircase. If you get a value with decimals, round it to the nearest whole number.
  4. Then, divide the stair height with the calculated steps. Do not round off the number after calculating to maintain a precise distance.
  5. Multiply the value derived from the previous step by the desired width to get the "run" of the stairs. The IRC recommends a 10-inch width for each step.
  6. Following the Pythagorean theorem, add the squared value of the stair rise and run lengths. Then get the square root of the value derived.
  7. You will need to multiply the value from the previous step to get the length of the stringers.

After getting the measurements, you can proceed to cut your stringers.

How To Cut Basement Stair Stringers

Before you start cutting, you have to prepare these supplies:

  • Measuring tools
  • Wood clamps or tape
  • Carpenter's square
  • Circular and hand saws
  • A straightedge (either a ruler or a strip of wood)
  • 2 x 12 lumber boards

Revisit the measurements of the stringers. To cut the stringers, do each of the following steps:

  1. First, you need to lay flat the carpenter's square with the point at the middle facing away from you.
  2. Use a straightedge to align the step rise and run. Place the tool on the legs of the square. Then use a clamp or tape to keep it in place.
  3. Align the created triangle on the edge of a 2 x 12 board or any lumber size chosen. Outline the board as a guide when cutting.
  4. Next, cut the board with a circular saw a little more than the desired stringer length. Use the triangular guide in step 2 to cut down the stringer run length in a zigzag method. When chopping off the last few inches of each step, use a handsaw.
  5. To create other stringers, use the first completed stringer as an outline on top of another board. Cut the board in the same way in step 4. Repeat until you have the number of stringers you need.

If you do not have the expertise in measuring and cutting stair stringers, you can ask a professional to do the job. You can also buy stock stringers from your local hardware for convenience.

How Many Stair Stringers To Use For A Basement Staircase?

Gorgeous stair balusters and a brown stair stringer leading to the basement

The next thing to decide is the number of stair stringers to use. The factors to consider include:

1. Stair Tread Thickness

The thickness of stair treads dictates the necessary stringer support. Relevant codes suggest at least 1 to 1.50 inches thick for the treads. The type of material you choose also varies in thickness. You can select from ply or hardwood to steel.

From there, if you have thicker treads, you will need fewer stair stringers. If you decide to have 4 stringers, the treads are thinner than those for a 3-stringer staircase.

If you bought synthetic treads, you could place stringers with a space ranging from 8 to 12 inches apart. You can refer to the manufacturer's instructions to allow a closer distance.

2. Stair Width

Most require the stringers to be at most 16 to 18 inches apart. If you have a 3-foot wide stair, you will need 3 stringers. For slightly wide stairs (like 3 feet and 6 inches), you will need 4 stringers. For stairs less than 40 inches (3.33 feet), you can either have one stringer or two for both sides of the stairs.

Check out our previous post to learn How Wide Do Basement Stairs Need To Be?

3. Stair Stringer Type

You should also identify the type of stair stringer. By doing so, you will also find out how to distance the stringers for the stairs.

The common types of stair stringers are as follows:

  • Notched/Routed/Hollow/Box - This type has notches that you can attach to the treads and risers.
  • Sawtooth/Open/Cut - This stringer has the rise and run of the stairs exposed when you view the sides.
  • Mono/Center beam - Supports the center of the treads because there are no risers for this kind of stairs. Based on its name, you will only need one stair stringer.

4. Live Load

Along with the previously mentioned factors, the live load can affect the number of stringers to use. The 2018 IBC suggests the stairs withstand at least 300 pounds or 100 pounds per square foot. You can refer to a guide from Boise Cascade for allowable stair stringers.

What Size Lumber To Use For Stair Stringers?

Following the IRC 2018 standard, the usual cut for stair stringers is 2 x 12 inches. It is still acceptable to use 2 x 10, but it might not be wide enough to accommodate larger notches. There are also 2 x 8 sizes, but this is not feasible for the 3.50-inch rule.

A narrow room with stairs on the side leading to the second floor

The stair stringer should be at least 3.50 inches wide at its thinnest point or the throat. This measurement is enough to support the load of the stairs.

As much as possible, you should choose high-quality and pressure-treated lumber for the stairs. If wood stringers do not appeal to you, read through the next section about other materials you can use for stair stringers.

What Materials To Use For Stair Stringers?

Unfinished stairs outside a two story white siding house

Whether you want to maintain the functionality or add design to your stairs, you can choose from various materials. Select the suitable material for the stair stringers from this list:

  • Steel - Even if common for industrial and outdoor use, you can choose steel for the basement stair stringers. You have the option for galvanized or stainless steel stringers. This material is great for basements with high traffic and weight loads.
  • Aluminum - This material resists corrosion, a plus factor for basement stairs. Unlike steel, aluminum is cheaper, lighter, and flexible.
  • Wood - You can use hardwood like oak, maple, or hickory for stronger support. Yellow pine and other pine boards are weaker and cheaper but still support well. If you want to save and get more benefits, you can buy engineered wood.
  • Laminated lumber (LSL/LVL) - Unlike ordinary lumber, LVL/LSL is better in durability, strength, and stability. The properties of this material prevent the warping and shrinking of the stringers.

You have the freedom to choose the stringer material to match your needs.

In Closing

A wood stair stringer block at the construction site

Stair stringers support the stair treads and risers. To measure the stringers, you need to get the total rise and run lengths. Afterward, the values derived will be the basis for outlining and cutting the stair stringers. If you don't want to cut, you can buy pre-cut stringers.

The stair stringer you need depends on factors like stair width, tread, stringer type, and load. The thicker the tread, the fewer stringers you need. Most follow a rule of at least one stair stringer for every 16 inches of the stringer width. You also need to get the correct lumber size if you choose wood stair stringers.

By following the process of creating stair stringers, you can have a sturdy and safe basement staircase.

You can explore more posts about basement stairs here:

How To Insulate Under Basement Stairs

Do Basement Stairs Need A Door?

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