🏗 Mono Stringer Stair Calculator
Turn rise, run, width, spine size, and support spacing into a cleaner mono stringer layout before fabrication.
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A mono stringer stair is an staircase that uses a single central support beam for the stair, often referred to as the spine of the stair. The treads of a mono stringer stair extend from each side of the central support beam; thus, the treads are referred to as cantilevered. Mono stringer stairs is typicaly employ in moddern lofts, deck runs, and in narrow spaces, as mono stringer stairs require less width to build than traditional stairs.
Traditional stairs require side stringers to support the treads and the individuals that walks on the stairs; mono stringer stairs, however, only use the central support beam to provide the necessary support to the treads and the individuals using those stairs. To build a mono stringer stair, it is first necessary to calculate the total rise and the total run of the stairs to be built. The total rise is the distance between the lower floor to the upper floor to which the stairs will rise, and the total run is the horizontal distance that the stairs will cover.
How to Build a Mono Stringer Stair
Should the builder incorrectly calculate the rise and the total run, the stairs may either be too steep or too shallow for comfortable use. For comfort, stairs are typically built with a rise of seven inches and a tread depth of ten-and-a-half inches. If the stairs are to be built in a location where space is very limited, the stairs may have a steeper pitch; however, stairs with a steeper pitch will cause individuals to tire more quick while climbing the stairs.
In addition to calculating the rise and the run of the stairs, the builder must calculate the size of the central support beam. The builder must calculate the depth and width of the support beam; the wider the stairs, the more leverage is placed upon the support beam. Additionally, the length of the support beam must be calculated.
Additional material must be provided to the support beam for flashing into a landing at the top of the stairs and for embedment of the support beam into the floor at the bottom of the stairs. Four inches of material should be provided at the top of the support beam for flashing into the upper floors landing, and six inches of material should be provided at the bottom of the support beam for embedment into the lower floor. If this additional material isnt provided for the support beam, it may be necessary to splice the support beam in the middle of the stair run; however, splicing the support beam in the middle of the stair can lead to a weak mono stringer stair.
Another factor that must be considered in the building of a mono stringer stair is the spacing of the support beams along the central support beam. The supports should be even along the central support beam of the stairs. Supports are typically placed every 12 inches to 16 inches along the central support beam; however, the length of the stairs will impact the exact placement of the supports.
For example, if the stairs are 48 inches in length, four supports will be placed along the central support beam, each 16 inches in distance from each other. The material that is used for the support beam will also impact the required spacing of the supports. For example, support beams made of HSS steel tubing are stiffer and have a greater ability to span greater distances than support beams made of aluminum.
Thus, if the builder utilizes aluminum beams in the construction of the mono stringer stair, the supports should be placed closer together than if HSS steel beams are used. Furthermore, if the mono stringer stair is to be built outdoors, the material from which the support beams will be constructed must be able to withstand the weathering of galvanized steel. Another consideration in the construction of the stairs is the overhang of the treads and the cantilever of the stairs.
The cantilever is calculated by taking half of the total width of the stairs and subtracting the width of the central support beam. The calculated number is then given the depth of the overhang of the treads; typical overhangs are between one and one-and-a-half inches deep on each side of the stairs. An overhang of this size will create what is referred to as a shadow line along the stairs.
An overhang that is less than two inches deep will make the treads appear short; however, if the overhang is more than two inches deep, the stairs may feel risky if they are constructed with a support beam that is not relatively thick. Prior to the construction of a mono stringer stair, it is always recommended to create a template for the stairs. A template can be built out of plywood; cutting the stairs to the size of the template will ensure that the stairs will have the proper pitch.
Additionally, walking on the template will allow the builder to ensure that the pitch of the stairs is comfortable prior to the placement of any expensive materials for the stairs. Using the template will also allow for any errors in the alignment of the treads or in the pitch of the stairs to be corrected. Additionally, the thickness of the treads and the overhang of the treads can be inspected to ensure that each side of the stair has the same thickness and overhang; this will ensure that the edges of the treads are even.
Finally, prior to the construction of the stairs, it is important to ensure that the stairs will meet all building codes. For instance, building codes require that a stair inspection is performed if the risers are more than 7.75 inches in height. Additionally, the rhythm of the stairs should also be considered; the code requires that two times the height of the riser plus the depth of the tread should be between 24 inches and 25.5 inches.
By ensuring that the stairs meet all of these requirements, the mono stringer stair will be both safe and structurally sound. You should of checked the dimensions twice.
