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This document assists in inspecting indoor or outdoor circular or curved stairs, railings, landings. Circular stairs have been used for centuries to ascend or descend towers or to provide access between floors where there is not enough horizontal space for a conventional straight-run or single-turn stairway. But circular and curved stairs present some special trip and fall hazards that should be carefully addressed.
Readers of this material about circular stairs and stair kits should also review the building code and trip hazards discussed at Winder stairs - stairways that include a turn without a landing platform. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
Circular & Curved Stairway Tread Inspection, Building Code, & Trip Hazards
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The traditional circular stairway shown in our photo at left was observed in Barcelona, Spain. This circular stairway accesses four floors in a building and uses stone treads that gave good traction except when they were wet during cleaning. The hand-rail was grasp-able and enclosed. Our opinion was that this was a good stair design. As we elaborate at Railings on Stairways, while a good handrail is important at every stairway, on curved or circular stairs where treads are not uniform in tread depth, railings are more likely to be grasped by stair users - and are perhaps even more critical. |
Circular Stair Kit Choices and Tips
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Which way to face the circular stair: The sketches at left show the basic construction of a typical circular stair kit. The right-hand sketch explains a "right hand" circular stair layout. Notice that for most circular stairwells, the user enters and exits the stairway facing in the same direction. This "direction facing" detail for circular stairs is important when determining where to place the stairwell, since you don't want your user to reach the top of the stairway and find herself facing a wall. Install the widest possible circular stairway: When we installed the circular stair shown at page top in the 1970's we had intended to save floor space by ordering the smallest-diameter available circular stair that we could buy. The stair company's expert advised installing the largest circular stairway that would fit in our building. Our own calculations had failed to consider just how small the individual stair tread walking space would be. |
After dividing the width of the stair opening in half (since treads have to be placed on either side of the center support post) and after subracting the diameter of the supporting stairway post, our four-foot diameter circular stair kit was able to provide a triangular stair tread which was about 21" across in its long dimension (post to outer tread edge). The 21" stair tread gave us about ten inches of comfortable walking space near the outer third of the tread, and a tread depth between 12" and 7".
If we had opted for the smallest diameter stair, the comfortable walking area on the triangular treads would have been substantially reduced to just a few inches, increasing the trip hazard of the stairs.
How will you move large furniture or other objects between floors? Having inspected a few A-frame cabins whose upper floor was accessible only by a single circular stairway, we had learned that it is difficult to impossible to carry the box-spring for a bed up a circular stairway. (We once had to saw a box spring in half, fold it doubled, and then repair it when we got it upstairs.)
When we built a second floor addition on our laboratory building and knowing that the indoor stairwell would be a 4-foot diameter circular stair, we included a second means of entry to the upper floor: a large outdoor stairway and landing.
Notes on Curved Stairways
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Above we provide a photo and a sketch of a curved stairway with unsafe railing enclosures and of curved stair tread designs. The sketch of curved stair treasds is courtesy of Carson Dunlop.
Because walking close to the outer railing places the user on the smallest tread area (highest trip hazard) it's most important to have a good grasp-able handrail here as well.
Balusters as Circular Stair Safety Enclosures / Barriers
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On our 1970's circular stair kit shown at page top and at left, the standard stair balusters were placed 11 3/4" apart - a child hazard by modern standards. None of our kids fell through the stairs, but we were worried about visitors. Our dog Katie did fall out of these balusters and to the floor below. Retrofit balusters or child guards would be a good safety improvement for this stairwell. For details about balusters (vertical spindles in railing construction) see details at Railings for a discussion of safety barriers along stairs, and Guards (railings on landings and open hallways, porches, screened porches, balconies that are more than 30" above floors or grade). As our photo shows, a toddler (in this case very carefully held and supervised) can easily fall through open landing balusters or open balusters on a stairway. We often see guards and railings enclosed using horizontal members or mesh or link fencing materials. Because a toddler can easily climb these materials, they are not safe for guard or railing enclosures and should not be used. Examples of unsafe horizontal rail and guard enclosures can be seen at Balusters. |
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- Daniel Friedman - principal author/editor of the InspectAPedia® Website
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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
STAIRS, RAILINGS, LANDINGS, RAMPS
Attic stairs
Balusters & Railing Enclosures
Basement Stairs & Walkout Covers
Books on Stair Construction
Checklist for Stair Inspections
Circular & Curved Stairs
Codes for Stairs
Exterior stairs
Fire Stopping for Stairways
Guardrails on Balconies & Landings
Lighting over Stairs
Pet Stairs
Railings on Stairways
Ramps, access
Stair dimensions: width height &c
Stairway headroom
Stairway landings
Step riser dimensions
Step stringer defects
Step tread dimensions
Stair tread nose dimensions
Winder stairs
- Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
- Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
- "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
- 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 sales@lawyersandjudges.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.
- The following stair books and other books on stair history, design, and architecture can be purchased at our Amazon-Supported InspectAPedia Bookstore
- Steps and Stairways, Cleo Baldon & Ib Melchior, Rizzoli, 1989.
- The Staircase: History and Theories, John Templar, MIT Press 1995
- The Staircase (two volumes), John Templar, Cambridge: the MIT Press, 1992.
- "The Dimensions of Stairs", J. M. Fitch et al., Scientific American, October 1974.
- ...
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