Why a Ramp Threshold Retrofit Is a Different Problem Than New Construction
This article is for contractors, facility managers, and architects who are adding or replacing a wheelchair ramp threshold at an existing commercial door opening. New construction gives you control over the floor finish height, the door undercut, and the frame rough-in. A retrofit gives you none of that. You are working around floors that are already down, a door that is already hung, and a frame that is not moving. The decisions that matter most happen before you place an order.
What Is a Wheelchair Ramp Threshold?
A wheelchair ramp threshold is a floor-mounted transition device that uses an angled ramp surface on one or both sides of a raised saddle to bring a wheelchair, walker, or foot-traffic user over a level change at a door opening without an abrupt step. The profile replaces a standard saddle threshold when the height change at the opening exceeds what ADA and ICC A117.1 allow to be left vertical or simply beveled.
Under ADA and ICC A117.1, a threshold change in level greater than 1/4 inch and up to 1/2 inch must be beveled at no steeper than a 1:2 slope. A change over 1/2 inch must be ramped. When a ramp threshold is used, the ramp faces transition the height change at an accessible slope so the opening meets the code requirement in a compact, floor-mounted footprint rather than a full built-up ramp assembly.
The Retrofit Measurement Problem: Three Numbers That Must Agree
Before specifying any ramp threshold for an existing opening, you need three measurements and you need them to work together. Getting one wrong means the threshold either fails the ADA height limit, prevents the door from closing cleanly, or creates a new trip hazard.
- The floor height differential. Measure the actual change in floor elevation at the sill line, from the low side to the high side. This is the number that determines whether a ramp profile is required at all and what height threshold is appropriate.
- The door bottom clearance. Measure from the bottom of the door to the finished floor surface at the highest point the threshold will occupy. Standard installation guidance calls for careful measurement here because the door must not drag or be impeded through its full closing cycle. A threshold that is too tall for the existing undercut will either prevent positive latching or damage the door bottom on every cycle.
- The opening width. Ramp thresholds are manufactured in standard widths. The threshold must fit tightly between the jambs. An undersized threshold leaves gaps at the jamb returns that become a trip point and a water infiltration path on exterior openings. Measure the clear dimension between jamb faces at the floor, not the door leaf width.
What a 2-1/2-Inch-High Ramp Threshold Actually Means at an Existing Door
A ramp threshold profile that rises 2-1/2 inches at its peak is not a threshold that sits 2-1/2 inches above the finished floor on both sides. The ramp faces slope up from the floor surface to the peak. That peak, however, is still a 2-1/2-inch obstruction at the door sill line.
At an existing opening, that peak height must clear the bottom of the door when the door is in its normal closed and open positions. If the existing door was hung with a 3/4-inch bottom clearance to a flat floor, a 2-1/2-inch ramp threshold will not fit under it without modification. The door will need to be cut down or rehung, or the threshold height must be reconsidered. This is one of the most common retrofit miscalculations in the field.
The solution is not always to select a shorter threshold. If the floor height differential genuinely requires the ramp profile, the door modification is the answer. Confirm that door modification is feasible before the threshold ships, not after.
The Width That Gets Ordered Wrong
Ramp thresholds for accessible openings are commonly available in 30-inch and 36-inch widths, among other sizes, to match standard door widths. A 30-inch-wide threshold is sized for a door opening with approximately 30 inches of clear sill width. It is not sized for a 32-inch clear opening door or a 36-inch door leaf.
On a retrofit, confirm whether the 30-inch dimension refers to the threshold body width or the opening it serves. If the floor opening between jambs is wider than the threshold, you may need a custom length cut or a different catalog width. Ramp thresholds cut in the field can compromise the ramp profile geometry if the cut is not made correctly, so getting the right width from the factory is the better approach when lead time allows.
Exterior vs. Interior Retrofit Conditions
Whether the opening is interior or exterior changes the installation requirements significantly.
Exterior Openings
- Water drainage path must be maintained. A ramp threshold that traps water against the door bottom accelerates frame corrosion and undermines weatherstripping performance.
- Fastener selection matters. Anchor the threshold to the substrate using fasteners appropriate for the floor construction type. Concrete slab installations require masonry anchors; wood subfloor installations require different fastener patterns.
- Caulk the threshold at both jamb returns after installation to prevent water infiltration under the threshold body.
- Verify that the door bottom sweep or automatic door bottom is compatible with the new threshold profile. A sweep calibrated for a flat saddle may not seal correctly against a ramp profile peak.
Interior Openings
- The ramp threshold must transition smoothly to the finished floor surface on both sides. If flooring has been installed up to the frame on one side but not the other, the ramp face may be landing on a subfloor elevation rather than a finished elevation. Recheck measurements after finished flooring is down.
- In healthcare and school renovation projects, the floor finish material on each side of the threshold often differs. Confirm that the ramp face geometry accommodates the actual finished floor height on both sides, not just the structural slab elevation.
Code Context: When a Ramp Threshold Satisfies ADA and When It Does Not
A wheelchair ramp threshold resolves the level-change requirement at the door sill. It does not resolve maneuvering clearance requirements, door opening force requirements, or hardware height requirements at the same opening. ADA compliance at a door is a system-level determination, not a single-product determination.
The code thresholds to keep in mind:
- Maximum 1/2 inch total threshold height on accessible routes in new construction.
- For existing or altered thresholds, up to 3/4 inch is permitted if beveled on each side with a slope no steeper than 1:2.
- A level change over 1/2 inch requires a ramp, which is what a ramp threshold profile provides within a compact footprint.
- The slope of the ramp faces must not exceed 1:12 to qualify as an accessible ramp.
If the building official or accessibility inspector is reviewing the opening, be prepared to demonstrate that the ramp threshold profile meets the slope requirement, not just that a ramp-style product was installed. Have the product documentation available at close-out.
Pairing the Ramp Threshold With the Right Door Bottom
A ramp threshold does not seal the door bottom gap on its own. The door sweep or automatic door bottom must make consistent contact with the threshold surface across the full width of the door. On an existing opening being retrofitted, the existing door bottom seal may have been sized and adjusted for the previous threshold profile. After the ramp threshold is installed, recheck the door bottom contact and adjust or replace as needed. Products from Pemko, Hager, and National Guard cover the range of door sweep and automatic door bottom options that work alongside accessible threshold profiles.
Getting the Specification Right Before the Product Ships
Ramp thresholds for commercial openings typically carry lead times measured in business days, not hours. An incorrect width or height selection on a retrofit project means a delay that hits the punch list. Measure the opening carefully, confirm door bottom clearance with the threshold in place before ordering, and verify that the ramp face slope meets the accessible route requirement for the jurisdiction.
DoorwaysPlus carries ramp threshold profiles from National Guard and comparable lines across standard and custom widths. If the opening dimensions are unusual or the project involves matching an existing threshold family, contact the team for a quote on the right profile before you order.