Keep current on stair codes, industry standards, safety, and best practices.
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Keep current on stair codes, industry standards, safety, and best practices.
Staircase construction comes with a host of decisions that have to made. What type of staircase is being built? What are the best materials to use for the various components? What are the best styles use for the different staircase parts? In this article we will examine the best material for stair stringers and the different types of stair stringers.
When it comes to staircase terminology, most people are familiar with treads (which you step on) and risers (vertical portion of the stair between each tread). But what exactly are stringers?
A stringer is the vertical support board or structural member that runs along each side or center of the staircase. The treads and risers are fixed into the stringer. Different stringers can combine with different types of stair treads to provide an almost endless combination of stair designs.
When located on either side of the staircase, the inner stringer is located against the wall, while the outer stringer is on the side of the staircase open to view. In some cases, the stairway may be in the center of the space with two outer stringers.
Stair stringers are constructed in a variety of materials and styles and finishes that can contribute to the look and functionality of the staircase.
The best material for a stair stringer depends on both the functionality of the staircase and the look desired. Steel, aluminum and various types of wood are common materials used for stair stringers.
Steel is an alloy made up of iron, carbon and other materials which can rust. To prevent rusting, galvanized or stainless steel is often used. Galvanized steel features a long-lasting zinc coating to prevent corrosive materials from reaching the steel below. With stainless steel, chromium, nickel, nitrogen and molybdenum are added to enable the steel to resist corrosion.
Steel stair stringers are popularly used in staircases in homes, business and industrial areas. Steel stringers can also be used in outdoor applications, especially if made of galvanized or stainless steel. Prefab metal stairs with steel stringers are a good option if the staircase needs to be able to stand up to heavy weight use, such as in industrial applications. Bolt-together metal stairs use formed steel stringers for a functional, lightweight metal stair system. Structural steel stair stringers are used in the design and manufacture of commercial stairs.
Unlike steel, aluminum is natural element that is corrosion resistant without any type of treatment. Aluminum is also lighter than steel.
Aluminum stair stringers can used in a variety of industrial, commercial and residential staircases.
Wood stair stringers come in different types of natural wood including oak, maple and walnut. Stair stringers can also be made from pressure treated or engineered wood. Wood stair stringers can be pre-cut for easier installation or uncut if a custom installation is preferred.
Wood stair stringers are normally found in residential or commercial buildings. In addition to their use as a support structure for the staircase, wood stair stringers add a warm and natural look to the room or environment.
Just as stair stringers can be made from different kinds of materials, they can also be built in different styles and types. The difference in styles depends on the type of stair design, the function and use of the stair, and the material used for construction of the stairs.
Commercial and industrial stair stringers are usually made of steel, aluminum, or stainless steel. Common styles for these stair stringer materials include:
Double stair stringers include two stringers each at the outside of each stair tread. The double stair stringer is the most common stringer style for commercial and industrial stairs. The design is used for prefabricated stair systems and can work with many types of stair railings. Steel stairs designed with double stringers often use structural steel shapes:
Double stair stringers are commonly used for egress stairs in commercial buildings, for industrial stairs, and for residential metal stairs. The double stringer design provides added support to meet engineering requirements to ensure a safe and durable design.
Center beam stringers are a type of mono stringer used in high-end feature stairs for offices, hotels, and other highly visible locations. This type of stringer uses a single beam, usually steel or stainless steel, that sits underneath the stair treads and provides the support for the stairs. Steel and stainless steel I-beams or HSS tube are common shapes used to fabricate center beam stringers.
Center beam stringers are a common type of stringer in monumental and feature staircases. The stringer is attached to the underside of the stair stringers and runs down the center of the flight.
Closed stair stringers are referred to by many different names including routed, housed, side and box stringers. This type of stringer is positioned outside the treads and risers so that the stairs are contained in between the two stringers. Closed stair stringers feature notches in which the treads and risers can be inserted. With this type of stringer, the edge of the tread is not visible and the vertical parts of the handrail (made up of balusters and newels) are typically attached to the top of the stringer.
Closed stair stingers can be used for staircases just about anywhere – in homes, commercial buildings and industrial applications. Closed stair stringers are commonly used for outdoor stairs.
Open stair stringers are also called cut or sawtooth stringers. When viewed from the side the treads are exposed. When open stringers are used in staircase construction, the balustrade supporting the handrail is set directly on top of the steps.
Open stair stringers are used in environments where the staircase needs to be visually appealing, including in residences and commercial buildings. They are not usually found in industrial settings.
As the name suggests, a mono stringer staircase uses a single but heavy-duty stringer beneath the center of the treads to support the staircase. Mono stingers are normally metal and welded to each tread with a bracket. All staircases with mono stringers have open risers.
Mono stair stringers are mostly used in modern homes and office buildings to achieve a contemporary look and are commonly used on spiral staircases.
A variation of the mono stair stringer is a twin stringer. In this case, two thin stringers take the place of the mono stringer. They are usually placed about 6” apart in the middle of the stairs. They can also be placed off center to create a more striking look.
Like mono stair stringers, twin stair stringers are mostly used in contemporary residences and offices to achieve an open, modern look.
A staircase with a cantilevered stringer features a single side stringer which is in mounted inside a wall and reinforced. The treads, which are supported by the stinger, protrude from the wall and the staircase is normally open on the other side.
Cantilevered stair stringers are used in homes and offices to achieve a stunning architectural effect.
Staircase stringers are the part of the stair which provides support for and houses the treads and risers. The type of materials used for the stringers, as well as the style of the stringers, will affect the look of the staircase. A staircase with a closed stair stringer made of steel or wood may be utilized more for function that style. Other types of stair stringers such as open, mono and cantilever provide the opportunity for more dramatic and contemporary looks.
At least one stringer is needed for a stair designed with a center or mono stringer underneath the stair treads. Two stringers are used with a double or twin stringers positioned to the outside of the stair treads.
Stair stringers may need additional support depending on the length of the stair stringer and the width of the staircase. Wood stair stringers typically need additional supports between 6' and 10' lengths while metal stair stringers typically do not require additional supports.
The maximum stair stringer length depends on the material used for stringer construction, the stringer size, and the stair building code requirements. IBC stair code limits stair stringers to a maximum vertical height of 12' in a single run.
You can build stairs without stringers if each stair tread provides it own structural support by constructing them as boxes or adding supports for each tread. Building stairs this way might be less economical than using stair stringers.