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Exterior stairs constructed by D Friedman & Art Cady (C) Daniel Friedman Stair Stringer & Stair Tread Support Hazards
Stair Stringer & Tread Support Defects

Stair Stringer Installation & Stair Stringer Defects: structural & safety hazards in stair & stair tread supports. Photographs & descriptions of stair stringer & stair tread support defects.

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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- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

Stair Stringer Defects: structural & safety hazards in stair stringers & stair tread supports

Stair Collapse during renovation (C) Daniel Friedman Stair Collapse during renovation (C) Daniel Friedman

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.

What happened? The pre-constructed stairway was not adequately connected to the building framing around the opening at the stairway top.

 

[Click to enlarge any image]

Article contents

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.

Stair Tread Support Methods & Common Safety Hazards

Stairway Lighting requirements (C) Carson Dunlop Associates

  1. Stair treads can be placed directly on top of the horizontal surface of cutouts in the notched stair stringer. 

    This approach is very secure provided that the stringer depth is great enough and the cutout depth shallow enough that the remaining stringer material is strong enough to carry the weight of the stairway and its users (1-? arrow in sketch at left).

    [Click to enlarge any photo or sketch]

    Of course if the stairway is supported by securing the stringer to walls on both sides, this cutout depth weakness problem is mitigated or eliminated.

Notched stair stringer hazards include

Stringer notched too deeply
, leaving insufficient material to carry the weight of the stairs and stairway users. This defect is also called "overcut stair stringer" and it is more common when the stringer lumber depth is smaller than a 2x12. See details
at STAIR STRINGER NOTCHING TOO DEEP

Below: The pink arrows point to splits in this notched stair stringer - creating the risk of a tread collapse and stair fall injury.

Multiple defects and hazards at this stairway may have contributed to a stair-fall and injuries (C) InspectApedia.com

  1. Stair treads can be placed between the stringers and supported by cleats or supported in grooves routed (rabbeted) inside the un-notched stringer and cut to 1/2 the 2x stringer's thickness.

    If the stair treads are set into grooves routed into the stringer, in a 2x stringer the groove depth should be 1/2 the thickness of the stringer (typically 3/4") and additional support by cleats or by gluing and end-screwing through the stringer sides into the treads is good practice.

    Watch out: be sure that the stair tread cleats are not damaged, split, inadequately-fastened, or of inadequate material.

    While 1x lumber (3/4" thick) is sometimes used for tread cleats, using 2x lumber (1 1/2" thick) and pre-drilling the cleats to be sure that they're not split or damaged during installation can increase stair tread safety as can the use of construction adhesive.

    Several manufacturers offer steel stair tread supports or cleats that may be an acceptable alternative to wood tread cleats.

Stair tread connection to stringers: options include rabbeted notches, cleats, and notched stringers (C) InspectApedia.com Carson Dunlop Associates ... Basement stair treads supported by 2x3 cleats adequately fastened to stringers, not split (C) Daniel Friedman at InspectApedia.com ... Stair tread support cleat split - unsafe (C) Daniel Friedman at InspectApedia.com

Sketch of tread/stringer connections above provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ]. Used with permission. Photos by DJF.

  1. Stair treads butted against an un-grooved stringer inner face and then nailed or screwed through the stringer into the stair tread.

    Watch out: We do not recommend this stair tread approach as too often we find the treads break away from the stringer causing catastrophic stair tread collapse and perhaps serious injuries. Examples of this stair tread failure safety hazard are shown just below.
    If you encounter a stair built this way you should add glued & screwed cleats to support the treads.

    Also see UNSAFE STAIR TREAD TO STRINGER CONNECTIONS

Wood stair tread collapse (C) Daniel Friedman at Inspectapedia.com ...

Photo above: a catastrophic stair tread collapse caused by inadequate tread support: the treads were end nailed through the stringer; treads separated and collapsed, leaving rusty nails protruding through the stringer side, potentially adding to the injuries of someone using this outdoor exit stair. (There are of course multiple defects visible in this stairway.)

Photo below: a stair tread has separated from the stringer by about 1/2 inch at this end-nailed or side-nailed tread. Walking up or down this stairway invites a tread failure by bending the fastening nails, leading to a tread separation and collapse.

Stair tread side nailed through stringer can easily separate and cause serious injury (C) Daniel Friedman at InspectApedia.com

Common Stair Stringer Defect Photographs

support added to exterior deck stairs (C) Daniel Friedman

The stair stringer must be secured to the structure at stair top, stair bottom, stair sides, depending on where there are building surfaces present. In our photo a above someone has added an intermediate support below a long stair stringer.

Rotted basement stair (C) Daniel Friedman Stairway Lighting requirements (C) Carson Dunlop Associates

Sketch above provided by Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ]. Used with permission.

Rotted stair treads or stringers

Rotted stair stringer (C) Carson Dunlop Associates

Our photo of a severely rotted stair stringer (above) is provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ]. Used with permission.

The image shows a rotted stair stringer and treads, open stair guard, flimsy and possibly not-graspable handrailing: obvious hazards at this exterior stair.

Watch out: 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 Hazards

Stairway Lighting requirements (C) Carson Dunlop Associates

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 of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

Unsafe Stair Stringer to Framing Connections

Stair stringer illustrastion (C) Carson Dunlop Associates at Inspectapedia.com used with permission

Click to enlarge Carson Dunlop Associates ' sketch of basic stair parts to read some details about stair stringers. Carson Dunlop Associates is a Toronto home inspection, education, and report writing tool company.

Where the stair abuts a building wall on at least one side, that stringer is normally nailed or screwed to the building wall framing, giving a very solid support on that side of the stairway.

But particularly at decks or porches or some basement entryu stairs where niether side of the stairway abuts a building wall, we sometimes come across stair stringers that are poorly-connected to the building framing.

The upper or top end of the stair stringer is connected to the framed stair top opening or to the deck or porch rim joist using either framing connectors or appropriate nails or construction screws.

Common defects we find at abutting wood framing member connections, including at the top (and sometimes bottom) of stair stringers include

You can see that there are many opportunities to make a bad connection using either approach, in particular, using improperly-sized, placed, or number of fasteners. There is no evidence in my experience that people make fewer mistakes using a joist hanger than using direct nailing.

For suggesting that more detail was needed on this topic, special thanks to Dov Ber Kahn, a home inspector in Rockland County, NY has contributed photographs of various building features. Mr. Kahn is a licensed home inspector in New York and New Jersey, and can be reached at Website: Kahnbhomeinspectors, Tel: 845-445-8234, Email: kdovber@googlemail.com

Steel Framing Connectors Used for Stair Stringer Connection to Structure

Several companies produce stair stringer framing connectors including Simpson Strong-Tie.

The Simpson LSC stringer connector we illustrate below can be used (by flipping it around) as a left side or right side bracket so that the connector can be concealed from the inside of the stair stringer - useful where the framing lumber is left exposed.

DeckLok® stair stringer connectors discussed at InspectApedia.com

USP Stair Stringer connector from uspconnectors.com at InspectApedia.com

Simpson Strong-Tie LCS Adjustable Stair Stringer Connector at InspectApedia.com www.strongtie.com

Simpson Strong-Tie LCS Adjustable Stair Stringer Connector at InspectApedia.com www.strongtie.com

Unsafe Stair Tread-to-Stringer Connections

Stairway Lighting requirements (C) Carson Dunlop Associates

Unsafe connections between stair treads and stringers  is also often hidden: check for:

Sketch courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

Also see Stair Tread Support Choices & Relation to Stair Stringer Notching at the top of this article.

Deck Stair Stringer Notching Too Deep

Unsafe exterior stair stringer and riser height (C) Daniel Friedman

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:

Research on Structural Stair Framing Connectors & Connections

Stair Tread Support Choices

This subtopic has been expanded and moved to STAIR STRINGER SPECIFICATIONS

 


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