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WOOD FLOOR DAMAGE
Stair stringer & stair tread support defects & safety hazards: this document provides specifications, sketches, photographs, and examples of improperly constructed or otherwise damaged stair and stair tread supports. Our photo at page top shows a wood exterior stair during construction by the author D. Friedman and associate Art Cady.
Because of the tricky uneven ground and the difficulty of accurately measuring rise off of a rough slope, the builders set the downhill stringer in place first, and determined remaining stair construction measurements based on the location of that stringer. Railings and balusters are incomplete in the photo.
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Definition of stairway stringer
What is a stair stringer? the stair stringer is the diagonal supporting structure that carries the weight of the stair assembly as well as people using the stairs. In our page top photo you can see the stair stringer that used 2x lumber. Stringers are typically notched to accept stair treads, or treads may be mounded on cleats secured to the stringer interior face.
You can see a stair stringer along the upper-edge of the set of stairs lying on their edge in our photo at above-right, after the stairs fell from the stair opening (our photo at above left) during a building renovation project. The stair stringer is secured to the structure at stair top, stair bottom, stair sides, depending on where there are building surfaces present.
You can see a stair stringer along the upper-edge of the set of stairs lying on their edge in our photo at above-right, after the stairs fell from the stair opening (our photo at above left) during a building renovation project.
The stair stringer is secured to the structure at stair top, stair bottom, stair sides, depending on where there are building surfaces present.
Our photo of a severely rotted stair stringer (above-left) is provided courtesy of Carson Dunlop Associates as is the drawing at below right. Used with permission.
Watch for rot in wooden stairs, especially at exterior entrances and decks. Where the stair stringer is mounted against a building wall water is often trapped, leading to hidden rot and sudden collapse.
Our photo shows rotting basement stair treads; from the stair top we could see that the entire stairway was twisting and in danger of sudden collapse. The sketch, courtesy Carson Dunlop, predicts stair rot exactly where it's found in our photograph.
This exterior stair ascending to a deck used a stringer pair that was so bouncy the builder decided to retrofit additional support at mid-span of the stair stringer.
A post secured to a pier and to the stringer side on each side of the stairway may have been a stronger solution.
We like to set posts at mid span as well as at the bottom landing quite securely to prevent unsettling movement when descending or ascending a tall exterior wood-framed stair such as this one.
Notice also the obsolete side railings which are not child-safe.
Stair stringer movement, as we cited just above, can lead to separation of the connection between treads and the stringer, leading to stair collapse.
Examine the stringers for bowing and look for gaps at the ends of treads - but beware: separation and gaps may be hidden if the stair treads were set into groove routed into the stringer.
Sketch courtesy Carson Dunlop Associates.
Unsafe connections between stair treads and stringers is also often hidden: check for:
Sketch courtesy Carson Dunlop Associates.
Also see Stair Tread Support Choices & Relation to Stair Stringer Notching at the top of this article.
The stair stringer is too-deeply notched and could split by the simple effect of weight of a user walking on these steps. Other defects in this horrible deck step construction include:
This subtopic has been expanded and moved to STAIR STRINGER SPECIFICATIONS
Continue reading at STAIR RISE & RUN CALCULATIONS or select a topic from the More Reading links shown below.
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