Accessibility Requirements When Adding Dwelling Units to Existing Structure

Last updated April 2, 2025
By Ian Story

This article reviews the condition where an existing structure is being split into multiple dwelling units. We discuss when accessible units are required and what upgrades need to be made to the existing structure.

Typically, multifamily buildings require Type B accessible units once there are 4 or more dwelling units in the building. When converting an existing building, the existing building code (IEBC) applies, and may modify some of these requirements. We also reviewed the Fair Housing Act Design Manual, which can separately require accessible units. The FHA does not apply to buildings first occupied before March 13, 1991, and only covers additions when 4 or more units are added (page 11).

To apply the requirements of the code, you first need to determine the extents of the work area, which can be tricky. The IEBC definition is below, followed by links to discussions about how to apply it.

WORK AREA: That portion or portions of a building consisting of all reconfigured spaces as indicated on the construction documents. Work area excludes other portions of the building where incidental work entailed by the intended work must be performed and portions of the building where work not initially identified by the owner is specifically required by this code [IEBC].

• Building Code Forum: Defining Work Area
• Building Code Forum: Work Area and its Effect on IEBC Compliance
• Building Code Forum: To Sprinkle or Not To Sprinkle (includes discussion of measuring reconfigured spaces)
• MA Building Official Interpretation of Work Area

This article assumes that the original building has no accessible units or common spaces. If these do exist, then any alterations or additions need to maintain the existing level of accessibility for the existing units and spaces. It also assumes there are fewer than 20 units total so no Type A units are required.

The IEBC requires you to provide Type B units under two conditions (and only if the final building will have 4 or more dwelling units):

1. The project adds 4 or more dwelling units. This provision doesn’t care about the total number of units in the building, just the number being added. The maximum number of Type B units required is equal to the number of units being added (306.7.10.3).
2. The work area exceeds 50% of the aggregate area of the building (306.5, 306.7.4). Under this provision, the maximum number of Type B units required is equal to the number of units being altered (306.7.10.3).

If either of those provisions is triggered, refer to IBC sections 1108.6.2.2.2 and 1108.7 to determine the specific number of Type B units required.

If full compliance with any accessibility requirements is technically infeasible, compliance is only required to the extent technically feasible. For the IEBC, technically infeasible is defined as follows:

TECHNICALLY INFEASIBLE: An alteration of a facility 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 which are in full and strict compliance with the minimum requirements for new construction and which are necessary to provide accessibility.