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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.
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 Choices & Relation to Stair Stringer Notching
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).
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.
Stair treads can be placed between the stringers and supported by cleats or supported by grooves routed inside the un-notched stringer.
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.
Stair treads butted against an un-grooved stringer inner face and then nailed or screwed through the stringer into the stair tread.
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. 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 later in this article.
Common Stair Stringer Defect Photographs
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 stringer poorly secured to the top landing of exterior porches and decks
Stringer loose, rotted, damaged, bowed, not secured to the building side wall where it should be, indoors or out
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.
Rotted stair treads or stringers
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 Hazards
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.
Unsafe connections between stair treads and stringers is also often hidden: check for:
Stair treads simply through-nailed from outside the stringer into the ends of the tread. We've seen such stair treads suddenly collapse under load or collapse due to spreading between the stringers. The protruding nails can cause serious cuts while the stair-user is falling.
Stair treads using under-sized cleats and box nails below treads
Stair treads loose and falling because of separation between the stringers
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Eric Galow, Galow Homes, Lagrangeville, NY. Mr. Galow can be reached by email: firstname.lastname@example.org or by telephone: 914-474-6613. Mr. Galow specializes in residential construction including both new homes and repairs, renovations, and additions.
 "The Elimination of Unsafe Guardrails, a Progress Report," Elliott O. Stephenson, Building Standards, March-April 1993
 "Are Functional Handrails Within Our Grasp" Jake Pauls, Building Standards, January-February 1991
 Access Ramp building codes:
 Access Ramp Standards:
ADA (Americans with Disabilities Act), Public Law 101-336. 7/26/90 is very often cited by other sources for good design of stairs and ramps etc. even where disabled individuals are not the design target.
ANSI A117.4 Accessible and Usable buildings and Facilities (earlier version was incorporated into the ADA)
ASTM F 1637, Standard Practice for Safe Walking Surfaces, (Similar to the above standard
 Falls and Related Injuries: Slips, Trips, Missteps, and Their Consequences, Lawyers & Judges Publishing, (June 2002), ISBN-10: 0913875430 ISBN-13: 978-0913875438 "Falls in the home and public places are the second leading cause of unintentional injury deaths in the United States, but are overlooked in most literature. This book is unique in that it is entirely devoted to falls. Of use to primary care physicians, nurses, insurance adjusters, architects, writers of building codes, attorneys, or anyone who cares for the elderly, this book will tell you how, why, and when people will likely fall, what most likely will be injured, and how such injuries come about. "
 The National Institute of Standards and Technology, NIST (nee National Bureau of Standards NBS) is a US government agency - see www.nist.gov
"A Parametric Study of Wall Moisture Contents Using a Revised Variable Indoor Relative Humidity Version of the "Moist" Transient Heat and Moisture Transfer Model [copy on file as/interiors/MOIST_Model_NIST_b95074.pdf ] - ", George Tsongas, Doug Burch, Carolyn Roos, Malcom Cunningham; this paper describes software and the prediction of wall moisture contents. - PDF Document from NIS
 Slips, Trips, Missteps and Their Consequences, Second Edition, Gary M. Bakken, H. Harvey Cohen,A. S. Hyde, Jon R. Abele, ISBN-13: 978-1-933264-01-1 or
ISBN 10: 1-933264-01-2,
available from the publisher, Lawyers ^ Judges Publishing Company,Inc., www.lawyersandjudges.com email@example.com and also from the InspectAPedia Bookstore (Amazon.com)
 The Stairway Manufacturers' Association, (877) 500-5759, provides a pictorial guide to the stair and railing portion of the International Residential Code. [copy on file as http://www.stairways.org/pdf/2006%20Stair%20IRC%20SCREEN.pdf ] -
 Mold-Resistant Building Practices, advice from an expert on how to prevent mold after a building flood and how to prevent mold growth in buildings by selection of building materials and by anti-mold construction details.
 "The Dimensions of Stairs", J. M. Fitch et al., Scientific American, October 1974.
 Stair & Walkway Standards for Slipperiness or Coefficient of Friction (COF) or Static Coefficient of Friction (SCOF)
ASTM D-21, and ASTM D2047
UL-410 (similar to ASTM D-21)
NSFI 101-B (National Floor Safety Institute)
NSFI Walkway Auditing Guideline (WAG) Ref. 101-A& 101-B (may appear as ANSI B101.0) sets rules for measuring walkway slip resist
OSHA - (Dept of Labor CFR 1910.22 does not specify COF and pertains to workplaces) but recognizes the need for a "qualified person" to evaluate walkway slipperiness
ADA (relies on the ANSI and ASTM standards)
 A. Sacher, International Symposium on Slip Resistance: The Interface of Man, Footwear, and Walking Surfaces, Journal of Testing and Evaluation (JTE), ISSN: 1945-7553, January 1997 [more focused on slipperiness of polished surfaces
 Algae is widely recognized as a slippery surface - a Google web search for "how slippery is algae on steps" produced more than 15,000 results on 8/29/12)
 Slipperiness of algae on walking surfaces, warning, Royal Horticultural Society, retrieved 8/29/2012, original source: http://apps.rhs.org.uk/advicesearch/profile.aspx?pid=418
 Slipperiness of algae: "Watch your step, wet rocks and algae are slippery" Oregon State University warning 1977 retrieved 8/29/2012, original source: http://www.worldcat.org/title/watch-your-step-wet-rocks-and-algae-are-slippery/oclc/663683915
 Coefficient of friction of algae on surfaces [like stair treads]: Delphine Gourdon, Qi Lin, Emin Oroudjev, Helen Hansma, Yuval Golan, Shoshana Arad, and Jacob Israelachvili, "Adhesion and Stable Low Friction Provided by a Subnanometer-Thick Monolayer of a Natural Polysaccharide", Langmuir, 2008 pp 1534-1540, American Chemical Society,
retrieved 8/29/2012, Abstract: Using a surface forces apparatus, we have investigated the adhesive and lubrication forces of mica surfaces separated by a molecularly thin, subnanometer film of a high-molecular-weight (2.3 MDa) anionic polysaccharide from the algae Porphyridium sp. adsorbed from aqueous solution. The adhesion and friction forces of the confined biopolymer were monitored as a function of time, shearing distance, and driving velocity under a large range of compressive loads (pressures). Although the thickness of the dilute polysaccharide was <1 nm, the friction was low (coefficient of friction = 0.015), and no wear was ever observed even at a pressure of 110 atm over 3 decades of velocity, so long as the shearing distances were less than twice the contact diameter. Atomic force microscopy in solution shows that the biopolymer is able to adsorb to the mica surface but remains mobile and easily dragged upon shearing. The adhesion (adsorption) of this polysaccharide even to negatively charged surfaces, its stable low friction, its robustness (high-load carrying capacity and good wear protection), and the weak (logarithmic) dependence of the friction force on the sliding velocity make this class of polyelectrolytes excellent candidates for use in water-based lubricant fluids and as potential additives to synovial fluid in joints and other biolubricating fluids. The physical reasons for the remarkable tribological properties of the ultrathin polysaccharide monolayer are discussed and appear to be quite different from those of other polyelectrolytes and proteins that act as thick “polymer brush” layers.
 Jason R. Stokes, Lubica Macakova, Agnieszka Chojnicka-Paszun, Cornelis G. de Kruif, and Harmen H. J. de Jongh, "Lubrication, Adsorption, and Rheology of Aqueous Polysaccharide Solutions, Langmuir 2011 27 (7), 3474-3484
 "Coefficients of Friction for Ice", The Physics Factbook™, Glenn Elert, Ed., retrieved 8/29/12, original source: http://hypertextbook.com/facts/2004/GennaAbleman.shtml
 "Coefficients of Friction for Ice", The University of the State of New York Reference Tables for Physical Setting/Physics. New York: The State Education Department, 2002. Op. Cit.
 Serway Physics for Scientists and Engineers 4th edition (p. 126.)
 "How Slippery Is It", retrieved 8/29/12, original source http://www.icebike.org/Articles/howslippery.htm
 John E. Hunter, "Friction Values", The Source, Society of Accident Reconstructionists, Winter 1998. Study of frictional values of car tires involved in collisions on snow or ice covered roadways.
 Frictional Coefficients of some Common Materials and Materials Combinations, The Engineering Toolbox, retrieved 8/29/2012, original source: http://www.engineeringtoolbox.com/friction-coefficients-d_778.html [copy on file as Friction and Coefficients of Friction.pdf ]
 Stairways and Ladders, A Guide to OSHA Rules, OSHA, U.S. Department of Labor, 3124-12R 2003 - Web Search 05/28/2010 original source: http://www.osha.gov/Publications/osha3124.pdf. OSHA regulations govern standards in the construction industry and in the workforce Quoting from OSHA whose focus is on workplace safety and so excludes discussion of falls and stair-falls in private homes:
OSHA estimates that there are 24,882 injuries and as many as 36 fatalities per year due to falls from stairways and ladders used in construction. Nearly half of these injuries are serious enough to require time off the job--11,570 lost workday injuries and 13,312 non-lost workday injuries occur annually due to falls from stairways and ladders used in construction. These data demonstrate that work on and around ladders and stairways is hazardous. More importantly, they show that compliance with OSHA's requirements for the safe use of ladders and stairways could have prevented many of these injuries. -osha.gov/doc/outreachtraining/htmlfiles/stairlad.html
 International Building Code, Stairway Provisions, Section 1009: Stairways and Handrails, retrieved 8/29/12, original source: http://www.amezz.com/ibc-stairs-code.htm [copy on file as IBC Stairs Code.pdf]
 Model Building Code, Chapter 10, Means of Egress, retrieved 8/29/12, original source: http://www2.iccsafe.org/states/newjersey/NJ_Building/PDFs/NJ_Bldg_Chapter10.pdf, [copy on file as NJ_Bldg_Chapter10.pdf] adopted, for example by New Jersey. International Code Council, 500 New Jersey Avenue, NW, 6th Floor, Washington, DC 20001, Tel: 800-786-4452
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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