the following learning objectives to focus your study while reading
this month’s ARCHITECTURAL RECORD / AIA Continuing Education article.
reading this article, you will be able to:
Describe what factors are involved in selecting materials for
List the code requirements for
exterior stair design.
Discuss stair design in historic
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.
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.
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."
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.
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.
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,"
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.
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.
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.
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."
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."
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
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.
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
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.
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.
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.
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.
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."
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.
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.
Capital City Landing in White River State Park
Architect: Wallace Roberts & Todd, Philadelphia;
Sasaki Associates, Watertown, Mass. (preliminary design)
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.
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
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.)
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,"
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
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.
Grace Episcopal Cathedral, San Francisco
Architect: Turnbull, Griffin & Haesloop Architects
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.
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."
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."
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.
comes to stairs, safety is first priority
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
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
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.
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."
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
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.
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.
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.
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.
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.
the sum of the tread and riser to be between 17 and 18 inches,
with the riser as little over 7 as possible.
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.