ResourcesContinuing Education

Creating Safe and Appealing Public Stairs

Architects agree that stairs are among the most challenging building components to design, and exterior public stairs are most complex of all.

by Wendy Talarico and Barbara A. Nadel, FAIA

Continuing
Education

Use the following learning objectives to focus your study while reading this month’s ARCHITECTURAL RECORD / AIA Continuing Education article.

Learning Objective:
After reading this article, you will be able to:

1. Describe what factors are involved in selecting materials for exterior stairs.

2. List the code requirements for exterior stair design.

3. Discuss stair design in historic surroundings.

4. List the common cause of lawsuits related to stair design.

By 1993, the once monumental stairs that lead from downtown Troy, N.Y., to Renssalear Polytechnic Institute (RPI) looked like some kind of ancient ruin. The bricks that once supported the treads showed the effects of countless freeze/thaw cycles, and the bluestone treads had slipped from their beds, a few of them cracked and spalled. Built in 1907, the flight of 163 steps had problems from the start, thanks to the soft brick used for the leveling beds. Regular maintenance kept problems in check until after World War II, when labor became scarce. Finally the stairs were abandoned, a cascade of rubble in the midst of the city.

Ongoing maintenance for stairs like those in Troy is just one of many issues to consider when designing public exterior stairs. Other dilemmas: Will the stairs hold up under weather extremes? Are they safe? Do they complement the building or surroundings to which they lead? Where should the handrails go? "In no other part of the building, except perhaps the facade, is it more important to weigh the upkeep and long-term benefits of what you're designing against construction costs and budget limitations," says Jonathan Woodman, AIA, of Woodman Associates Architects in Newburyport, Mass. Stairs take a beating from weather, traffic, and even skateboarders and rollerbladers. Yet designing them to last and ensuring good maintenance can protect the architect and building owner from being sued.

A federal grant came to the rescue of the stairs in Troy. Architecture Plus, also in Troy, was retained by city and RPI officials to rebuild the stairs. The firm started by shoring up the masonry foundation and replacing the original brick setting bed with concrete. Underdrains conduct water away from the substrate to help prevent water damage. Many of the old tread stones were reused, though getting them perfectly square was impossible. "We had to do some false work to conceal the imperfections," says Francis Murdock Pitts, aia, principal in charge at Architecture Plus. "But using the old stones retained the historic character of the stairs and saved money."

The project was completed in the autumn of 1999 and has become a gathering place for local residents and RPI students, who study, sunbathe, and socialize on the steps. As a case study, the stairs in Troy prove the importance of durable materials and proper maintenance.

What the codes say
The three model codes and their amalgamation, the International Building Code, have slightly different design requirements for public stairs. Codes also vary according to occupancy and building type; healthcare facilities have different requirements than apartment buildings or stairs located as part of a public plaza.

Some rules relating to public stairs and commercial structures are consistent throughout all codes, however. Exterior stairs must be stable, slip resistant, and noncombustible. Open risers are forbidden and solid treads are required. Stairs should be protected from weather, specifically snow and ice, though there are many ways to do this that don't require a roof or canopy, says Kim Paarlberg, staff architect for Building Officials Code Administrators International (BOCA). For example, simply placing them out of the path of winter winds may be enough. Proof of a reliable snow-removal method, such as heated treads or a dedicated maintenance staff, is also acceptable. "The code official must be convinced that it is possible to egress in an emergency situation, regardless of the weather," she adds.

The width of the stairs, usually recommended to be a minimum of 44 inches, may also be dictated by code. This depends on the use of the building and the number of occupants.

The Americans with Disabilities Act (ADA) guidelines say continuous handrails, necessary anytime there are more than two treads, must flank the shortest route to a building's main entry. In this sense, the rails provide some direction to those who have mobility impairments or who lack the stamina to get to the door in a more roundabout way. They also act as a guide for the visually impaired. Twelve-inch-minimum railing extensions at the top and bottom (plus the width of the bottom tread) of the run signal the beginning and end of the steps.

There are also specific criteria that describe shape and height limitations for the gripping surface. The outside diameter of the rail must have a radius of 11/2 inches. A four- or six-inch spacing is required on the guardrail, "so that children cannot stick their heads through and possibly fall to their death if the stair is high enough above ground," Paarlberg says. An additional rail at a lower height is recommended by the ADA for buildings widely used by children.

Historic buildings pose special code concerns, especially when it comes to handrails. "Most are out of compliance due to their size and gripping surface-if there are railings at all," says John G. Waite, faia, of Albany, N.Y. Following codes while renovating old stairs may alter the character of the building, however. In New York, for example, codes say handrails must be located at four-foot intervals across broad flights of stairs. All those handrails may alter the character of the stairs significantly. "It's essential that architects work with code officials to make some compromises for old buildings," Waite says. "That doesn't mean making them unsafe or inaccessible; just more appropriate."

Materials matter
What the stairs are made of should be consistent with the construction of the building or surrounding structures. "Monumental buildings should have monumental stairs," says Steven Winkel, faia, of Field Paoli Architects in San Francisco. "Stone buildings should have matching stone stairs when possible."

Material choices depend on aesthetics, cost, maintenance needs, and climate. In northern climates, just about every surface material is problematic. Masonry, concrete, and stone can fall victim to freeze/thaw cycles, like the stairs in Troy. The material used for the substrate contributes to the stairs' overall durability. Concrete is the most common and cost-effective substrate. Steel may be used but is susceptible to corrosion, particularly in climates where chemicals are used for de-icing.

Cast-in-place concrete stairs, perhaps with precast elements, such as treads, are an adequate solution for many buildings (although concrete is also somewhat susceptible to damage from de-icing chemicals). Integrally colored concrete further enhances the aesthetics. Adequate drainage, specifically weep holes, proper slope, drainage channels in some cases, and a gravel bed beneath the concrete, helps avert moisture and subsequent cracking problems. To prevent slips, a coarse finish is used on the tread surface. And with concrete, as well as other tread materials, a slope of about 2 percent or 1/4 inch of rise per foot of run is necessary to prevent ponding on the treads.

Different tread and riser materials may be used over concrete or steel substrates, though this adds to the cost. Stone is used frequently, or granite, limestone, and high-quality bluestone. Marble is also used, though it is slippery and usually softer than other stones, making it more vulnerable to freeze/thaw cycles. Brownstone is used on historic buildings, though it is more likely to spall than other types of stone.

Stone pieces can be set in mortar, though this requires careful installation to avoid an uneven tread surface and to keep mortar joints small, limiting moisture penetration. Using large stones minimizes the number of joints and means fewer opportunities for water penetration.

In designing new stairs for the Temple Emanu-el in Haverhill, Mass., Woodman used one piece of granite with no joints for each tread. It was expensive, says Woodman, "but these are '100-year steps' that will require minimal maintenance." Also, winter shoveling won't dig into any joints, chipping out the mortar. And the large pieces of stone were easier and faster to install.

Among handrail materials, bronze, brass, and cast iron are ideal for high-quality buildings, such as courthouses. All three are likely to last indefinitely-and are priced accordingly. Steel is common but is more susceptible to corrosion. To prevent rust it should be both galvanized and painted, though the paint is likely to chip and wear with daily use. Epoxy paint is durable but susceptible to ultraviolet degradation. Topping it with a urethane finish coat solves this problem.

Metal railings can react to the salts used to melt ice, which mix with snow and water to form a corrosive solution. Problems are compounded with stone surfaces as the corrosive solution makes stains and can cause the stone to delaminate.

But it's not my fault!
Exterior stairs used to play an important role in the aesthetics of the building. Think of the Capitol, the New York Stock Exchange, the great cathedrals of Europe, and all those Beaux-Arts libraries and museums. "In the old days, buildings were placed high for grandeur of scale," Winkel says. "Now, buildings are pushed close to the ground to minimize grading and ramps. There are just too many legal issues so it's better to avoid them altogether."

While the number of falls that occur on outside stairs is not tracked specifically by insurance companies, about 25 percent of all claims deal with bodily injury, including slip-and-fall cases. According to Architectural Graphic Standards, stairs (indoors and out) result in 4,000 deaths and one million injuries annually. It is certainly not uncommon for architects to be sued, in turn, by building owners for negligent design, says Michael J. Maloney of Maloney & Company, an insurance brokerage and risk-management firm in Madison, Conn.

Meeting the local building code doesn't absolve the architect of liability. Code provides only a minimum requirement. Architects must look at unique site conditions, as well. For the new stairs at the Temple Emanu-el, Woodman knew he'd have to provide broad landings where people could congregate after services. Otherwise, members of the temple would try to meet on the steps and would be more likely to fall. While landings are normally required after a rise of 12 feet, Woodman recommends them every 5 to 6 feet, depending on floor-to-floor heights.

A good stair maintenance program is the best way to avoid liability problems, says Architecture Plus' Pitts. The owner and maintenance staff should be aware of potential slip and traction problems with maintenance coatings, such as overpolishing or oversalting the stairs. Good maintenance also means the stairs will last longer, look better, and minimize liability issues.

 

CASESTUDY

Project: Capital City Landing in White River State Park
Architect: Wallace Roberts & Todd, Philadelphia; Sasaki Associates, Watertown, Mass. (preliminary design)

Part of an ongoing upgrade of the downtown Indianapolis park and waterway system, the 25-acre Capital City Landing project includes a number of stair locations that link the walkways, bridges, and plazas lining the Central Canal and the White River. The project connects various sites within the downtown, including the zoo, a university, and government office buildings. It is also a favorite jogging route and a good place for workers and students to retreat at noon for an outdoor lunch.

Each stairway consists of granite pieces set on a concrete substrate. The locally quarried granite has a thermal or flame finish to minimize slipperiness. The roughened finish is accomplished by flaming the material with a torch after it is sawed in the quarry.

The steps have 14-inch treads and 6-inch risers, "comfortable proportions that match the natural range of human movement," says project manager Hank Bishop of Wallace Roberts & Todd. (The firm also worked on Baltimore's Inner Harbor, a series of parks and plazas that capitalizes on the waterfront.)

A set of amphitheater steps (with intermediate stairs for access) surrounds the turning basin, where tour boats will turn around. These use complementary proportions: risers are 18 inches and treads 42 inches. "People can sit on the steps with ample room for others to sit or pass behind them," Bishop adds.

The handrails are steel that's powder-coated in dark brown. The electrostatic powder-coating paint treatment is the most durable solution when stainless steel is not an option, he says. "The coating costs more than steel, but it's worth it."

The granite is similarly durable, though Bishop notes that the crisp edges of the nosing are becoming shiny after repeated scraping by rollerblades. "You can't do outdoor stairs these days without considering rollerbladers," he says.


 

CASESTUDY

Project: Grace Episcopal Cathedral, San Francisco
Architect: Turnbull, Griffin & Haesloop Architects

As aesthetic elements, stairs can serve many purposes. At this cathedral, which sits atop Nob Hill overlooking San Francisco, the renovated stairs became a way of connecting the structure, both physically and metaphorically, to the rest of the city.

According to Mary Griffin, aia, the cathedral was formerly accessed through a set of stairs tucked behind the chapter house. "That left little space to gather after services or to hold events. And it effectively blocked out the city, isolating the cathedral." The solution was to tear down the chapter house and create a stair that is, Griffin says, "a grand gesture and a generous statement."

Both the cathedral, built in the early 1900s, and the new stair are reinforced concrete. This was used on the stairs to help resist seismic forces. "There are expansion and contraction seams all over that will take up some of the stress also," says Eric Haesloop, aia. "If the cathedral were on base isolators, the seismic movement would be taken up with a moat at the base of the stair."

The architects used 6-inch risers and 12-inch treads-a little steep for an exterior stair, Haesloop says. But these dimensions allowed room for multiple landings. Other complications included finding a way to tie the stairs into the sidewalks and courtyards at various elevations on the sides of the building. "Coping with topography is always a problem when designing exterior stairs in San Francisco," Haesloop says.

 

When it comes to stairs, safety is first priority

Making exterior stairs safe not only benefits the building owners and occupants, it helps avoid liability issues if someone is injured. Some of the most common hazards:

  • The concrete atop metal-framed stairs wears away or is damaged by severe weather, exposing metal edges that catch on the front of the shoe.
  • Risers are not uniform in height, particularly at the top or bottom of the run. This breaks the natural, biomechanical rhythm of people going up and down the steps and they are more likely to trip.
  • Stairs are poorly lit. Good lighting makes safer and better-looking stairs, though it is often spotty and uneven. Placing lights at each tread is a good, thorough approach.
  • Stairs do not comply with ADA requirements, such as handrail size or position. Says Field Paoli Architects' Winkel: "Handrails and stairs are a slam dunk for disability advocates to find fault."
  • Single steps "are killers," Winkel adds. "It usually has no handrail, the most important cue that the stair is there. Consequently, people don't see the step and fall."
  • Stair edges are difficult to see. Some states require that public stairs in all facilities have a two-inch contrasting color strip set back one inch from nosing to make it easier to see the stair edge.

Riser and tread wars: What are the best proportions?

In the beginning, there were ladders. Then there were stairs-albeit uncomfortable ones, as anyone who's climbed the pyramid at Chichen Itza will report. Then came the front and the back stairs; the ones in front were grand and gradual while the back steps were steep and minimal.

Now there are building codes that dictate riser and tread minimums based on accessibility as well as stride and comfort studies. These studies say, in essence, that the tread should be wide enough for the entire foot, and the riser low enough that lifting the foot doesn't require excessive effort and discomfort.

Stair dimensions reflect the various purposes of the stairs. The facades of the U.S. Capitol, surrounded by steps, are a good example. Designed for the most part by architect Benjamin Latrobe, the various staircases have risers and treads of differing proportion. The stairs off the Senate and House wings are intended to be fast and functional-63/4 by 141/4 inches. But the ceremonial stairs on the Pennsylvania Avenue side are 5 by 171/8 inches.

Riser and tread proportions are also a matter of expediency. Inside and out, stairs are customarily designed to the steepest limits in order to use less space and material, says John Waite.

But personal preferences also come into the equation. "Two times the riser-height plus the depth of one tread equals 26 inches. It's what I like to use for a comfortable stride," says Hank Bishop of Wallace Roberts & Todd in Philadelphia.

Others prefer the sum of the tread and riser to be between 17 and 18 inches, with the riser as little over 7 as possible.

The British, French, and Germans have their own set of historic precedents for stair proportions, though the measurements are ultimately about the same as the 7-11 rule dictated by code. In Great Britain, a step is considered proper if the riser is 51/2 inches and the tread 12 inches. In Germany and France, smaller proportions are allowed, perhaps due to the fact that buildings in Central Europe are often tightly designed. For instance, a riser of 71/2 inches might be paired with a tread of just 9 inches. Small by American standards, but adequate in Germany.

Questions:

  1. What do building codes require for exterior stair design?

  2. What are the factors in selecting materials for exterior stairs?

  3. What are the considerations for handrail materials?

  4. What can architects do to avoid lawsuits regarding stairs?

  5. What are the considerations for stairs with historic buildings?

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