1.4 Technical Infeasibility, Existing-Building Ramps, and Historic Structures
Key Takeaways
Technically infeasible means structural conditions (removing a load-bearing member essential to the structural frame) or other physical or site constraints prevent full compliance; cost alone never qualifies.
A117.1-2017 Table 405.2 allows existing-building ramps steeper than 1:12 only where space is limited: up to 1:10 for a 6-inch maximum rise and up to 1:8 for a 3-inch maximum rise.
Historic structure alternatives apply when the authority having jurisdiction determines that compliance for routes, entrances or toilet rooms would threaten or destroy historic significance (2021 IEBC 306.7.16; 2024 IEBC 306.7.18).
Historic alternatives require one 36-inch exterior route from a site arrival point, a route to public spaces on the accessible entrance level, an unlocked or monitored accessible entrance, and one accessible single-user or family toilet room where toilets are provided.
Accessible means of egress and Type B units are not required in historic structures, and Type A units in individually owned R-2 units may meet Type B criteria.
1.4 Technical Infeasibility, Existing-Building Ramps, and Historic Structures
Candidates often blend three different forms of relief into one idea of "existing building exceptions." The exam separates them, so you should too:
- Technical infeasibility (IBC and IEBC definitions, IEBC 306.7): permits access "to the maximum extent technically feasible."
- A117.1 existing-building criteria: written exceptions such as steeper short ramps, smaller turning spaces and 54-inch existing reach ranges.
- Historic structure alternatives (2021 IEBC 306.7.16; 2024 IEBC 306.7.18): reduced requirements where full compliance would threaten or destroy historic significance.
Technically Infeasible
The IBC and IEBC define technically infeasible as an alteration that has little likelihood of being accomplished because the existing structural conditions require the removal or alteration of a load-bearing member that is an essential part of the structural frame, or because other existing physical or site constraints prohibit modification or addition of elements, spaces or features that are in full and strict compliance with the minimum requirements for new construction and that are necessary to provide accessibility.
| Claim | Technically infeasible? | Why |
|---|---|---|
| Widening a door requires cutting a load-bearing masonry pier essential to the frame | Yes | Structural condition in the definition |
| A ramp landing would extend past the property line onto a public sidewalk | Yes | Existing site constraint |
| An elevator would cost $250,000 | No | Cost is not in the definition |
| A ramp would spoil the facade | No | Appearance is not in the definition (unless historic alternatives apply) |
| The tenant would lose two parking spaces | No | Inconvenience is not a physical constraint |
Even when part of a requirement is infeasible, the rest is not. If a door can reach only 31 in. of clear width because of a structural column, the designer still provides the maneuvering clearances, hardware heights and opening force that are feasible.
A117.1 Existing-Building Criteria
A117.1-2017 builds many existing-building allowances directly into its technical sections. The ramp table is the most frequently tested.
A117.1 Section 405.2 limits ramp running slope to greater than 1:20 and not steeper than 1:12. The exception reads: "In existing buildings or facilities, ramps shall be permitted to have slopes steeper than 1:12 complying with Table 405.2 where such slopes are necessary due to space limitations."
| Running slope | Maximum rise |
|---|---|
| Steeper than 1:12 but not steeper than 1:10 | 6 in. |
| Steeper than 1:10 but not steeper than 1:8 | 3 in. |
There is no row for slopes steeper than 1:8. A 1:6 ramp allowance appeared in the 1991 federal ADA guidelines for historic buildings; it does not appear in A117.1-2017 or the IEBC, so a 1:6 slope is not a correct answer on this exam.
Worked Example
An existing tenant entrance has a 4-inch step and only 40 inches of available run.
- At 1:12, a 4-inch rise needs 48 inches of run, which does not fit.
- At 1:10, a 4-inch rise needs 40 inches of run, and 4 inches is within the 6-inch limit. This complies with Table 405.2 because space is limited.
- If only 30 inches were available, the slope would be 4:30, about 1:7.5, steeper than 1:8. That is not permitted, and a different solution such as a platform lift or relocated entrance is needed.
Other existing-building criteria to tab: 60-inch turning circle (304.3.1.2), 30 x 48 clear floor space (305.3.2), 54-inch side reach for existing unaltered elements (308.3.1 Exception 1), existing or altered thresholds up to 3/4 in. with beveled edges (404.2.4), a 5/8-inch latch-side stop projection in alterations (404.2.2 Exception 2), and existing elevator cars with 16 sq ft of floor area (407.4.1 Exception).
Historic Buildings
A historic building under the IEBC is one listed, or certified as eligible for listing, in the National Register of Historic Places, designated as historic under applicable state or local law, or certified as a contributing resource within a listed or designated historic district.
The 2021 IEBC (306.7.16) and the 2024 IEBC (306.7.18) say: where compliance with the requirements for accessible routes, entrances or toilet rooms would threaten or destroy the historic significance of the historic structure, as determined by the authority having jurisdiction, the listed alternatives for that element are permitted.
| 2021 / 2024 | Alternative requirement |
|---|---|
| 306.7.16.1 / 306.7.18.1 | At least one exterior accessible route, including curb ramps, from a site arrival point to an accessible entrance, 36 in. minimum width |
| 306.7.16.2 / 306.7.18.2 | An accessible route from an accessible entrance to public spaces on the level of that entrance |
| 306.7.16.3 / 306.7.18.3 | If an entrance cannot be made accessible under 306.7.5, provide an accessible entrance that is unlocked while the building is occupied, or a locked accessible entrance with a notification system or remote monitoring; IBC 1112 signs at public entrances and the accessible entrance |
| 306.7.16.4 / 306.7.18.4 | Where toilet rooms are provided, at least one accessible single-user or family/assisted-use toilet room complying with IBC 1110.2.1 |
| 306.7.16.5 / 306.7.18.5 | Same for bathing rooms |
| 306.7.16.6 / 306.7.18.6 | Individually owned Type A units in R-2 may meet Type B criteria |
| 306.7.16.7 / 306.7.18.7 | Type B units are not required in historic buildings |
Two exceptions apply to historic structures: accessible means of egress required by IBC Chapter 10 are not required, and the altered element or space is not required to be on an accessible route unless 306.7.16.1 or 306.7.16.2 requires it. Upper floors of a historic building therefore do not need an accessible route when the alternatives apply; only public spaces on the accessible entrance level must be connected.
Note
IEBC Appendix B adds supplementary provisions, including consultation with the State Historic Preservation Officer and displays located for seated viewing, but an appendix applies only where the jurisdiction adopts it. Under the base IEBC, the determination belongs to the authority having jurisdiction.
Case Study
A 1905 bank listed on the National Register becomes a restaurant. The monumental front stair cannot be ramped without destroying the facade, and the basement restrooms cannot be enlarged.
- The AHJ determines that a front ramp would destroy historic significance. A side entrance with a 36-inch exterior route from the parking lot becomes the accessible entrance, unlocked while occupied. Signs comply with IBC 1112 at the front entrance and at the accessible entrance.
- The dining room on the entrance level is connected by an accessible route.
- One accessible single-user toilet room is provided where toilet rooms are provided.
- The mezzanine bar is not required to be on an accessible route under the historic exceptions.
In an existing building with limited space, a designer proposes a ramp at a 1:9 slope to overcome a 5-inch change in level. Does this comply with ICC A117.1-2017 Table 405.2?
Yes, because slopes up to 1:8 are allowed for any rise in existing buildings
Yes, because slopes up to 1:6 are allowed for rises under 6 inches
No, because a slope steeper than 1:10 is limited to a 3-inch maximum rise
No, because slopes steeper than 1:12 are never allowed
Under the 2021 IEBC historic structure provisions, who determines whether compliance with the accessible route, entrance or toilet room requirements would threaten or destroy historic significance?
The authority having jurisdiction
The project architect
The U.S. Department of Justice
The building owner
A historic three-story library qualifies for the IEBC historic alternatives. Which statement about its upper floors is correct?
An elevator must reach every floor because a library is a public building open to all
A platform lift must serve the second floor at minimum
Only public spaces on the accessible entrance level need an accessible route
The upper floors must be closed to the public
Sections you finish are checked off in the contents.