PPP Notes - Exterior Stairs and Ramps

EXTERIOR STAIRS AND RAMPS

 

EXTERIOR STAIRS/RAMPS

 

• Throughout the centuries, stairs and ramps have been used to address elevation changes in the landscape.
• They can be heroic or modest, nuanced or straightforward, detailed or plain.
• They represent for designers opportunities to create delight, variety, viewpoints, and accents in the movement of people across a landscape.
• They are also zones for heightened access and safety consideration.
• This section leaves for the designer’s imagination the full potential of stairs and ramps as artistic design elements, and concentrates instead on access and safety design issues.

 

REGULATIONS

 

• Stairs and ramps as components of the pedestrian walkway system are regulated for minimum design standards at federal, state and local levels.
• With the ADA, the role of stairs and ramps in creating accessibility for all became a specific design focus.
• For designers, the first requirement is to thoroughly review the relevant jurisdiction’s accessibility and safety codes related to stairs and ramps.
• Any discrepancies between the information presented in this discussion and any regulation should always be resolved in the favor of the regulation.
• There are differences in the design requirements between local, state, and federal accessibility and safety regulations.
• Identifying and determining the relevant regulations for a project requires research and discussion with the project client.
• Private and local government projects usually must adhere to local, state, and federal requirements.
• State and federal projects usually exempt themselves from application of regulations enacted by lower jurisdictional levels.
• A review meeting early in the design process with the relevant building code enforcement group is advisable.  Determining the applicable regulations with the client is a professional liability responsibility of the design professional.

 

EXTERIOR VERSUS INTERIOR DESIGN STANDARDS

 

• Exterior stairs and ramps must deal with climatic issues that interior situations do not – obvious examples being rain and snow.
• In addition, the design and spatial variety of exterior landscape spaces make the location of stairs and ramps less predictable for pedestrians.
• Thus, in exterior design factors such as tread depth and slope, traction and detectable warning zones become important issues to consider.
• Directly applying interior stair and ramp standards to exterior locations is generally not a good practice.

 

EXTERIOR STAIR DETAILS

 

• A rule of thumb for tread depths and riser heights for exterior stairs can be translated to this equation:
• Height of Two Risers + Depth of One Tread = 26 Inches
• For exterior locations, a recommended range for risers is between 4 and 7 inches, with recommended tread depth of 12 and 18 inches.
• Stairs in exterior locations require a slope on the tread to shed rain and snow melt.  A generally recommended slope is a 2% slope from front to back of tread, or a ¼-in. on a 12-in.-wide tread.
• The leading edge of a step is called the step nose.
• Stairs nose details vary depending on the material used.
• Detailing of the stair nose is an important safety detail.
• The current accessibility standard is that step noses should have a radius of ½-in., with no overhang deeper than ½-in. on the step.
• The goal is to reduce the potential points where a person’s shoe could become trapped or tripped, such as a toe under a step overhang or a heel at a sharp nose edge.

 

CONSTRUCTION OF EXTERIOR STAIRS

 

• A construction concern for concrete stairs is the placement of reinforcing bars.
• Reinforcing steel should be placed a minimum of 3 in. back from any exposed surface of the step.
• Maintaining a minimum 3-in. clearance reduces the potential for breakup of the step due to differential freeze/thaw expansion between the reinforcing steel and the concrete.  This is especially important in the stair nose zone.
• Adding slip dowels and keyed joints at the top of concrete stairs to adjacent concrete paving or subsurface layers is a good construction detail, to avoid differential settlement and tripping hazards.
• The bottom step footing on concrete stairs or concrete subsurface for stairs should extend down, at a minimum, to the local freeze depth.
• Manufactured metal stair nosings are sometimes used in heavily trafficked locations to reduce the wear and tear on step noses.
• In climates with freezing temperatures, selecting a product and installation method that accounts for deferential freeze/thaw effects between the metal and the step material is important.
• Metal stairs in exterior locations should be built with open-mesh metal grating or with embossed or raised patterning on the tread surface, to provide traction and the ability to release rain or snow quickly from the surface of the step.
• When open-mesh metal materials are used on steps, the rule of ¼-in. maximum clear opening to provide safety for shoe heels is a good safety standard to follow.
• Exterior raised steps made with wood, plastics or composites do not require a tread slope if there is a ¼-in. to ½-in. gap between each wood member.
• This gap helps to release rain and snow buildup that can cause slipperiness.
• For timber steps that are laid on grade, selecting wood varieties and installation methods that resist moisture rot is important to achieve long-term durability.
• Cedar, redwood, and preservative treated woods are generally considered reliable selections for ground-laid timber steps.
• Gravel subsurface is often used in high-moisture environments to reduce the moisture buildup beneath ground-laid timber steps.
• Stone, when used in ground-laid steps, should be selected for flat tops and be large enough so that they do not overturn when pressure is applied at the step nose. 
• Lapping each stone step by approximately one-fourth to one-third of their tread depth helps to prevent this overturning.
• If laid with spacing between each stone step, each stone should be buried up to one-third the thickness of the stone, and be level on its top surface.
• Gravel beds or designed structural soil mixes such as base course should be considered whenever high moisture content or poor structural soil conditions exist.
• A solid subsurface contributes to the long-term durability and stability of a set of steps.

 

EXTERIOR STAIR RUNS, WIDTHS, AND LANDINGS

 

• Single steps should be avoided, as they create a tripping hazard because of their lack of visibility. 
• Stairs and steps in general should be distinguished from surround paving by a difference in material, color, or pattern, to highlight and make them more prominent. 
• In most jurisdictions, when there are more than three steps, handrails must be provided.
• As a general rule, exterior stair landings should, at a minimum, match the width of the stairs and be a minimum of 3 ft. deep.
• Exterior stairs when located at main entries or emergency exits of buildings should, at a minimum, be the width of the exiting doorways.  This helps to maintain a safe emergency egress zone.
• Providing a landing at doorways and gates that are served by stairs makes using doorways safer and more convenient.
• The swing of the door should be accounted for in scaling the depth of a landing, to avoid having to be on a step to open or close a door or gate.
• Installing intermediate stair landings where an elevation change of between 2.5 and 5 ft. has been reached on a run of stairs creates a comfortable resting place for users.
• When longer runs of stairs are used consideration for larger landings with opportunities for sitting should be given.
• Landings should be built with a minimum 2% slope toward the downhill edge.

 

RAMPS

 

• Accessible ramp slope standards initially were based on research using disabled adult males as the test population.  This means that, perhaps, it is not the best standard for the elderly, children, or the frail.
• Thus, for the greatest universal access of a project, designers should target for the lowest ramp slope rate practical.
• Research based on the elderly and children is beginning to show that a better slope rate for those populations is 1:16 or lower.
• The 1:12 or 8.333% slope rate should be considered the maximum rate, not the goal.
• As a practical cost consideration, any ramp that is flatter than 1:20 does not require handrails and, thus, can avoid that cost.

 

STREET RAMPS

 

• There are two common locations for exterior ramps: at street corners and crossings, and where grade changes occur. 
• The design of street ramps is highly regulated by local, state, and federal ordinances.
• This discussion does not provide street ramp standards because the design requirements are diverse and undergo frequent review and modification.
• Thus, for street ramp standards, the design professional is referred directly to the relevant ordinance determined by discussion with the relevant code enforcement agency and the client.

 

EXTERIOR RAMP DETAILS

 

• The most important design feature of an exterior ramp is the surface of the ramp.  Ensuring that it is not slick in wet weather is critical for safety.
• Follow these guidelines:
• On concrete ramps, the surface should be, at minimum, a medium broom finish, with the brook strokes being perpendicular to the flow of traffic.
• Stone clad ramp designs should consider honed or scored surfaces, and avoid any smooth, flat finish.
• Metal ramps designs should consider structural grille/grate panels or embossed or patterned metal, and avoid any smooth finish.
• Installing slip dowels or keyed joints at the tops and bottoms of ramps to adjacent paving helps to avoid differential movement that causes tripping hazards at the entries to the ramp.

 

RAMP WIDTHS AND LANDINGS

 

• Design guidelines for ramp widths and landings are as follows:
• An accessible ramp should have a clearance between ramp handrails of at least 36”, to allow a person in a wheelchair room for his or her hands to turn the wheels.
• A ramp landing should occur at a maximum of 30 ft. of run of a ramp.  The ramp landing must be a minimum of 60 in. clear depth.
• If ramps change direction at landings, the minimum landing size must be 60 in. by 60 in.
• If an exterior doorway is located at a ramp landing, the landing must comply with safety and access requirements for the door.

 

STAIRS AND RAMPS HANDRAILS

 

• As part of the accessible system, stair and ramp handrails are covered under access and safety regulations.  Their placement, height, length, strength, and safety details fall under the design guidance of these regulations.
• Thus, familiarity with the relevant codes is paramount.
• General requirements for all handrails are:
• The top of handrail to stair nose or ramp surface distance should be constant – a height between 34 and 38 in.
• The diameter of width of the handrail must be 1-1/4 in. to 1-1/2 in.
• Structurally, the handrail must be able to withstand 250 lb. of downward pressure per inch.
• The ends of handrails should not be sharp at the ends.
• General standards for stair handrails are:
• At the top of the stair run, the rail must be level for 12 in. before the first step nose.
• At the bottom of the stair run, the rail must extend for one tread length at the same slope as over the majority of the stairs, then remain level for an additional 12 in.
• General standards for ramp handrails are:
• At the top of the ramp, the rail must be level for 12 in. before the top of the ramp.
• At the bottom of the ramp, the rail must remain level for 12 in., beyond the end of the ramp.