Wheelchair clearance in BIM

What "wheelchair clearance" means in a BIM workflow

Clearance in a model is geometry a rule can read, not an annotation. If a dimension is not modelled, no checker confirms it and the drawing set becomes the only version of truth. Figures are from the 2010 ADA Standards, fetched 22 October 2026.

• Clear width. 403.5.1 sets 36 inches (915 mm) minimum, with an exception permitting 32 inches (815 mm) for a length of 24 inches (610 mm) maximum, provided reduced-width segments are separated by segments 48 inches (1220 mm) long minimum and 36 inches wide minimum.
• Ramp slope, rise and width. 405.2 limits ramp running slope to 1:12, 405.3 limits cross slope to 1:48, 405.5 requires 36 inches (915 mm) clear width measured between handrails where handrails are provided, and 405.6 caps the rise for any run at 30 inches (760 mm).
• Landings. 405.7 requires landings at the top and bottom of each ramp run, 405.7.3 sets a clear landing length of 60 inches (1525 mm) minimum, and 405.7.4 requires 60 inches by 60 inches minimum where the ramp changes direction.
• Turning space. 304.3.1 gives a circular space of 60 inches (1525 mm) diameter minimum; 304.3.2 allows a T-shaped space within a 60 inch (1525 mm) square with arms and base 36 inches (915 mm) wide minimum.
• Doors. 404.2.3 requires 32 inches (815 mm) minimum clear opening, measured with the door open 90 degrees. 404.2.4 and Table 404.2.4.1 set maneuvering clearances, which depend on approach direction and pull or push.
• Handrails. 505.4 sets the top of the gripping surface at 34 inches (865 mm) minimum and 38 inches (965 mm) maximum above the ramp surface. 505.10.1 requires ramp handrails to extend horizontally above the landing for 12 inches (305 mm) minimum beyond the top and bottom of the runs, and 405.8 requires handrails where the rise exceeds 6 inches (150 mm).
• Protruding objects. 307.2 limits objects with leading edges more than 27 inches (685 mm) and not more than 80 inches (2030 mm) above the finish floor to 4 inches (100 mm) maximum horizontal protrusion into the circulation path. Section 204 sets the general rule.

The three verification levels

1. Design intent in the model. The model is a design artifact. If the ramp is drawn as a sloped plane with no landing, or a door is placed without its swing, there is nothing for a later stage to check. This level asks whether the elements, parameters and levels in the model are what you designed.

2. Automated or rule-based checking inside BIM. Two families exist and are often confused. Native authoring checks (Revit warnings and errors) fire while you model, using parameters already in the file. Imported model rule checking works on an exported IFC, with tools such as Solibri or other IFC checkers applying a rule set to geometry and properties. The second family is more complete but depends on the export: property sets travel only if the authoring tool mapped them.

3. On-site verification. A surveyor measures the built condition. This is the only level that describes what exists, and where construction tolerances, as-built changes and missing handrails surface. Where the jurisdiction requires field verification, a clean model does not replace it.

A model check is not a compliance certificate. It proves the model satisfies the rules encoded in it, at the moment it ran. The authority in your jurisdiction decides what evidence it accepts.

Checklist before you issue drawings

Read each dimension from the standard in the last column, not from memory or an old drawing. Two habits speed the pass up: measure on the model's finished face level, not the structural level, and check door swings against the clearance zones in the same view, because a swing that looks fine in plan often eats the clearance Table 404.2.4.1 requires.

Common failure modes

• The drawing set says 1:12 but the model gives less. Often the ramp was modelled to a target level before the floor build-up was added, or the slope was drawn as a schematic annotation rather than a real sloped face. Re-measure the model face against the stated rise and run.
• The landing is missing. A ramp modelled as one continuous sloped plane has no level landing at the top or bottom of the run, so no place to turn or open a door.
• The door swing intrudes on the clearance. Swing arcs are often excluded from the model, so nothing flags the conflict until someone opens the door.
• The handrail is not modelled. With no handrail in the model, nobody checks its height or extension, and the clear width between handrails under 405.5 goes unverified.
• Corridor pinch points. Columns, joined wall types, services, signage and furniture each cut the width below what the annotation claimed.

Where to check the numbers

Dimensions differ between standards, so read every value from the text your project is judged against. Links checked 22 October 2026.

• 2010 ADA Standards for Accessible Design on ada.gov, with403 Walking Surfaces,404 Doors and Gateways,405 Ramps,304 Turning Space,505 Handrailsand307 Protruding Objects.
• U.S. Access Board on access-board.gov, the technical guidance behind the ADA guidelines:403.5.1 Clear Width,405 Ramps,404.2.4 Maneuvering Clearances,505.10.1 Handrail Extensionsand307.2 Protrusion Limits.
• ICC A117.1, the accessibility standard referenced by the International Building Code, is readable oncodes.iccsafe.org. It is a different text with different figures; do not mix clauses between the two.
• ISO 21542:2021, Building construction, Accessibility and usability of the built environment, is listed oniso.org. Its European adoption is EN 21542, published through CEN and CENELEC and sold by national standards bodies (CEN accessibility page:cencenelec.eu. ISO 21542:2021 relates its wheelchair dimensions to a commonly used footprint of 800 mm wide by 1300 mm long.

Where more than one regime governs, most teams design to the strictest applicable text and document which one governs. TheADA ramp requirements page collects the U.S. sections.

How this connects to a ramp calculator

A BIM check tells you whether your geometry is right. Aramp calculator tells you what it should be: enter the rise and it returns the run length for the slope ratio you need, the number of runs and landings, handrail and edge protection references, and a spec sheet. If the space is too short for a compliant run, theramp fit planner checks a straight run and suggests a switchback.

Sources consulted 22 October 2026: 2010 ADA Standards (ada.gov); U.S. Access Board (access-board.gov); ICC A117.1 (codes.iccsafe.org); ISO 21542:2021 (iso.org); CEN and CENELEC (cencenelec.eu). Clause references are given so you can read the current text, which may change after this guide.