An accessible route provides a continuous, unobstructed path connecting all accessible elements and spaces of a building or site. To be compliant, every component along this route must adhere to strict dimensional and slope requirements outlined in the International Building Code (IBC) and the referenced ICC A117.1 standard, Accessible and Usable Buildings and Facilities.

Here are the core requirements for designing compliant accessible routes:

Walking Surfaces: The running slope (in the direction of travel) of a walking surface must not exceed 1:20 (5%). The cross slope (perpendicular to the direction of travel) must not exceed 1:48 (approximately 2.1%).

Ramps: Any walking surface with a running slope steeper than 1:20 is classified as a ramp.

• Slope: The maximum slope for a ramp is 1:12 (8.33%).
• Rise: The maximum vertical rise for any single ramp run is 30 inches.
• Landings: Ramps must have level landings at the top and bottom of each run. Landings must be at least 60 inches long.
• Handrails: Handrails are required on both sides of any ramp with a rise greater than 6 inches.

Protruding Objects: To prevent hazards for people with vision impairments, objects mounted on walls or posts cannot project more than 4 inches into the circulation path if their leading edge is between 27 inches and 80 inches above the finished floor.

Changes in Level:

• Vertical changes up to 1/4 inch are permitted.
• Changes between 1/4 inch and 1/2 inch must be beveled with a slope no steeper than 1:2.
• Changes greater than 1/2 inch must be treated as a ramp.

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Why Accessible Route Design Matters

Properly designing accessible routes is not just a matter of checking boxes for a permit; it is a fundamental aspect of ensuring safe and equitable access for everyone. These requirements, primarily enforced through IBC Chapter 11 and its referenced standard, ICC A117.1, are closely aligned with the federal Americans with Disabilities Act (ADA) Standards for Accessible Design.

Failure to correctly detail slopes, landings, transitions, and clear paths can create significant barriers for people with disabilities and expose designers, builders, and owners to legal liability. Common pitfalls include:

• Miscalculating Slopes: Seemingly minor errors in calculating running or cross slopes can render a path unusable and lead to failed inspections.
• Ignoring Protruding Objects: Everyday items like fire extinguisher cabinets, wall sconces, and even some drinking fountains can become dangerous hazards if not properly located or detailed.
• Poor Site Coordination: The interface between the building (designed by the architect) and the site (often by a civil engineer or landscape architect) is a frequent source of non-compliance, especially at building entrances and curb ramps.

Understanding these rules is essential for architects, engineers, and inspectors to create truly inclusive environments, avoid costly rework, and navigate the plan review and inspection process smoothly.

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How do I correctly detail the intersection of an accessible route and a vehicular way where there is no curb ramp (e.g., a parking garage entrance)? What are the maximum allowable slope and cross-slope transitions according to A117.1?

The intersection of an accessible route and a vehicular way must be a flush, level transition. Where there is no curb, this is typically detailed as a "blended transition," which must meet the slope requirements for a standard walking surface.

According to ICC A117.1-2017 §403.3, the cross slope of the walking surface must not exceed 1:48 (2.1%). The running slope cannot exceed 1:20 (5%). Any change in level at the transition must comply with §303, meaning it cannot have a vertical offset greater than 1/4 inch. If the offset is between 1/4 inch and 1/2 inch, it must be beveled at a 1:2 slope.

Critically, where an accessible route crosses a vehicular way, a detectable warning surface is required. ICC A117.1-2017 §406.6 and §705 mandate a 24-inch deep field of truncated domes at the boundary between the pedestrian area and the vehicular area. This provides a tactile warning for individuals with vision impairments that they are entering a hazardous area.

In a parking garage, this means:

• The pedestrian path leading to the drive aisle must maintain a cross slope of 2.1% or less.
• The point where the pedestrian path meets the drive aisle must be flush.
• A 24-inch deep detectable warning surface must be installed along the entire edge of the pedestrian area that adjoins the vehicle lane.

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What is the maximum allowable cross slope for a walkway to be considered part of an accessible route under the 2009 ICC A117.1, and does this requirement change if the walkway is adjacent to a sloped street?

The maximum allowable cross slope for a walkway is 1:48, which is approximately 2.1%. This requirement is stated clearly in ICC A117.1-2009 §403.3 and remains unchanged in the 2017 edition.

This requirement does not change if the walkway is adjacent to a sloped street. The accessible route itself must remain compliant regardless of the surrounding topography. This is a critical and often challenging design constraint. If a street has a significant slope, the adjacent sidewalk must be designed to maintain a maximum 2.1% cross slope. This often requires:

• Grading the site to create a level path for the walkway.
• Installing retaining walls to separate the compliant walkway from the adjacent, non-compliant grade.
• Locating the accessible route further away from the sloped street edge.

Exceeding the 2.1% cross slope can make it difficult for a person using a manual wheelchair to travel without veering downhill and can create instability for users of other mobility devices.

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Does the projection of a wall-mounted fire extinguisher cabinet into a corridor violate the protruding object limits of ANSI A117.1 if the leading edge is below 27 inches but the cabinet itself is higher?

Yes, this configuration almost always violates protruding object limits and is a common design error. The rules in ICC A117.1-2017 §307 (Protruding Objects) are intended to protect individuals with vision impairments who use a cane to detect obstacles.

The logic is as follows:

• Cane-Detectable Zone: A cane sweep typically detects objects at or below 27 inches above the finished floor (AFF).
• Hazardous Zone: Objects with leading edges above 27 inches and below 80 inches AFF are above the cane-detectable range and can become head or shoulder hazards.
• Protrusion Limit: Any object with a leading edge in this 27"-to-80" zone cannot project more than 4 inches into the circulation path.

If a fire extinguisher cabinet projects 6 inches from the wall, its front face is a hazard. Even if the bottom edge of the cabinet is at 26 inches AFF, the portion of the cabinet above 27 inches still projects more than the allowable 4 inches. An individual using a cane would not detect the hazard before striking it.

To make this compliant, you must either:

• Recess the cabinet so it projects no more than 4 inches from the wall.
• Place a cane-detectable element below the cabinet. This could be a small ledge or decorative element with its leading edge at or below 27 inches AFF that projects at least as far as the cabinet above. This allows a cane user to detect the lower element and avoid the overhead hazard.

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How is the running slope of a curb ramp flare measured correctly in the field, and what is the maximum allowable slope for the flare if it lands in a pedestrian circulation path?

The running slope of a curb ramp flare is measured in the direction of the slope, which is typically perpendicular to the curb line. To measure it, place a 24-inch (or longer) digital level on the surface of the flare, oriented directly up and down the slope, to get an accurate reading.

According to ICC A117.1-2017 §406.3.2 (Flared Sides), if the sides of a curb ramp are flared, the slope of the flare cannot exceed 1:10 (10%).

This 1:10 maximum slope is critical when the flare is part of a pedestrian circulation path. This occurs when the sidewalk continues past the sides of the curb ramp. A person walking along the sidewalk would have to traverse the flare, making it a walking surface. A flare steeper than 1:10 in this location would create a tripping hazard and an unacceptably steep cross slope for the perpendicular path of travel. If the area next to the curb ramp is a non-circulating area, such as landscaping, the flare is not considered part of a pedestrian path and this slope limitation does not apply in the same way, though steep drop-offs should still be avoided.

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What is the steepest slope allowed for a ramp by the ANSI code?

For new construction, the steepest running slope allowed for a ramp in an accessible route is 1:12 (8.33%). This is explicitly stated in ICC A117.1-2017 §405.2 (Running Slope).

However, the standard provides exceptions for existing buildings and facilities where space constraints make a 1:12 slope technically infeasible. These exceptions, found in §405.2, allow for steeper slopes over very short vertical rises:

• A slope between 1:12 and 1:10 is permitted for a maximum rise of 6 inches.
• A slope between 1:10 and 1:8 is permitted for a maximum rise of 3 inches.

These exceptions should be used only as a last resort in alteration projects and require careful documentation of the technical infeasibility of achieving a 1:12 slope. They are not an option for new construction.

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How high can a threshold be before it needs to be beveled?

A threshold can have a vertical edge up to 1/4 inch high. If a threshold is higher than 1/4 inch, its edge must be beveled.

This requirement is detailed in ICC A117.1-2017 §303 (Changes in Level) and referenced by §404.2.4 (Thresholds) at accessible doorways. The rules are as follows:

• Up to 1/4 inch (6.4 mm): The change in level can be vertical.
• Between 1/4 inch and 1/2 inch (13 mm): The change in level must be beveled with a slope no steeper than 1:2 (one unit vertical to two units horizontal).
• Greater than 1/2 inch: The change in level is not considered a threshold and must be treated as a ramp, complete with landings and, if the rise is high enough, handrails.

The absolute maximum height for a threshold at most accessible doors is 1/2 inch.

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Additional Considerations for Accessible Route Design

Jurisdictional Variations: Beyond the Model Codes

While the IBC and ICC A117.1 provide the baseline, many states and large cities adopt their own codes with amendments that can be more restrictive. For example:

• California (CBC): The California Building Code has extensive unique accessibility provisions in Chapter 11A (for public housing) and Chapter 11B (for public accommodations). It often has more stringent requirements for detectable warnings and reach ranges.
• Texas (TAS): The Texas Accessibility Standards (TAS) are enforced by the Texas Department of Licensing and Regulation and are largely based on the ADA standards but have their own specific interpretations and administrative rules.
• Florida (FBC): The Florida Building Code, Accessibility, contains specific modifications to the national standards.

Always verify requirements with the local Authority Having Jurisdiction (AHJ) before finalizing designs.

Coordination is Key: From Design to Inspection

Designing a compliant accessible route requires seamless coordination among multiple disciplines:

• Architects & Civil Engineers: The handoff from the site accessible route (parking, public sidewalk) to the building entrance is a common failure point. Ensure that exterior grades, walkway slopes, and door landing levels align perfectly.
• Architects & MEP Engineers: Mechanical, electrical, and plumbing elements frequently create protruding objects. Fire alarm devices (strobes), thermostats, sconce lighting, and fire extinguisher cabinets must be located or specified to comply with the 4-inch projection limit.
• Specification & Construction: Correctly specifying products like detectable warning surfaces and compliant thresholds is as important as showing them on the drawings. During construction, field verification of slopes and dimensions by the contractor and inspection team is essential to ensure the design intent is realized.

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Common Mistakes in Accessible Route Design

• Averaging Slopes: A walkway might have an average slope of 5% (1:20), but if any section is steeper, it is a ramp and must comply with ramp requirements. Slopes must be measured at their steepest point.
• Ignoring Cross Slope on Turns: At 90-degree turns in a walkway, the cross slope of both paths must be maintained, which can be tricky to grade correctly.
• Forgetting Landings: A series of short ramps still requires compliant landings between each ramp run.
• Handrail Termination: Handrails must extend horizontally at the top and bottom of the ramp run. Forgetting these extensions is a common error.
• Non-Compliant Flares: Using returned curbs is often simpler and less prone to error than building compliant flared sides on curb ramps, especially where the adjacent surface is a walkway.

Frequently Asked Questions (FAQ)

What is the difference between a ramp and a sloped walkway?

A walking surface with a running slope of 1:20 (5%) or less is considered a sloped walkway. If the slope is steeper than 1:20, it is defined as a ramp and must meet more stringent requirements for landings, width, and handrails.

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Are handrails always required on ramps?

No. Handrails are required on both sides of a ramp only when the total vertical rise of the ramp run is greater than 6 inches.

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What is the minimum clear width for an accessible route?

The minimum clear width for an accessible route is 36 inches. However, wider paths (e.g., 60 inches for passing) are often required or recommended.

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Do I need a landing at the top and bottom of every ramp?

Yes. Every ramp run must have a level landing at the top and bottom that is at least 60 inches long and as wide as the ramp. Intermediate landings are also required for ramp systems with a total rise of more than 30 inches.

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Is ANSI A117.1 the same as the ADA Standards?

They are separate documents but are highly harmonized. The IBC and most state/local building codes legally enforce ICC A117.1. The Americans with Disabilities Act (ADA) is a federal civil rights law that enforces its own 2010 ADA Standards for Accessible Design. For most technical requirements, they are functionally equivalent, but designers should be aware of both.

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What are "detectable warnings"?

They are a standardized surface of truncated domes (small, flat-topped bumps) built into walking surfaces. They are required to warn people with vision impairments of upcoming hazards, such as entering a street or approaching a platform edge.

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Can an accessible route include stairs?

No. An accessible route must provide a path free of stairs. While stairs are required by code for egress, they are a barrier to accessibility. An accessible route must be provided via ramps, elevators, or sloped walkways in addition to any required stairs.

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References

1. ICC A117.1–2017: Accessible and Usable Buildings and Facilities (Official Standard – Digital Viewer): https://codes.iccsafe.org/content/icca117-12017/american-national-standard
2. 2010 ADA Standards for Accessible Design – Ramps, Curb Ramps, and Walking Surfaces (Sections 403, 405, 406, 303, 307): https://www.ada.gov/law-and-regs/2010-ada-standards-for-accessible-design/
3. IBC 2021 – Chapter 11 Accessibility (Scoping for Accessible Routes, Ramps, Landings, and Site Accessibility: https://codes.iccsafe.org/content/IBC2021P1/chapter-11-accessibility
4. US Access Board – ADA Accessibility Guidelines (ADAAG): Ramps, Walkways, and Detectable Warnings: https://www.access-board.gov/ada/guides/chapter-4-routes/
5. ICC Curb Ramp & Pedestrian Access Technical Guide (Curb Ramp Geometry, Flares, Detectable Warnings): https://www.iccsafe.org/advocacy/accessibility/accessible-means-of-egress-and-curb-ramps/

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