Interpretation #9457

Original Request

Code Version: 2023
Code: EXTBLDG
Code Description
Chapter: 11
Section: 1103.5.1.3.1
Topic: Lateral addition to pre-firm residential structure matching existing finished floor.

Question

Section 1103.5, 1.3.1 uses the term “addition”. Section two of the FBC/Existing Building defines “addition” as “extension or increase in floor area, number of stories, or height of a building or structure.” Because the term “addition” is used in 1.3.1 and is seemingly in direct opposition to the definition contained in the same publication, we believe that when the code section uses the verbiage “shall not create or extend any non-conformity of the existing building.” This should be construed to be more accurately stated as, “Shall not create or extend any (less conforming) non-conformity….” By using editorial assessment and adding the verbiage “less conforming”, this would clarify the meaning of the code section to not allow any construction that would be considered less conforming than the existing structure. (otherwise every addition would be considered non confirming and not be allowed, specific to this section) By using this new understanding of the code section, it would more closely align with the general understanding of the FEMA “50% rule”. As delineated in “FEMA P758 Table 6-1b “Lateral Addition, not SI “- any lateral addition does not have to comply”. The only substantive change from that long standing rule would be that the addition would be at or above the existing elevation of the lowest floor in the existing structure regardless of the original build date or pre/post firm as per FEMA.

Answer Published 11/06/2025 at 8:12 AM

The key to your answer is the meaning of these two words "create" or "extend". If the lateral addition is not a substantial improvement and the existing structure was built in compliance with applicable flood provisions, the proposed lateral addition, if not a substantial improvement, is permitted to be constructed at the same elevation as the existing structure, subject to any local floodplain ordinance requirements.

Commentary

The following commentary is offered by FDEM, with further explanation regarding "create" and "extend." FDEM plans to prepare and post guidance based on this. The FBC Existing Building defines “existing building” without regard for a specific date, such as date of the community’s first Flood Insurance Rate Map or date the community joined the NFIP. The FBC definition governs application of the flood provisions of the FBCEB. That means every building that is already constructed is subject to determining whether any repair, alteration, or addition (or combinations) constitutes Substantial Improvement or whether any damage is Substantial Damage. The phase “not create or extend” or similar is used in FBCEB, even in sections not about flood and not about additions. Here are two non-flood uses: • Chapter 5 Prescriptive Compliance, Sec. 502 Additions, Sec. 502.1 General: “Additions to any building …shall comply…for new construction. Alterations to the existing building…shall be made to ensure that the existing building or structure together with addition are no less conforming than...was prior to the addition,” • Chapter 11 Additions, 1101.2 Creation or extension of nonconformity: “An addition shall not create or extend any nonconformity in the existing building to which the addition is being made….” Note that in FBCEB Sec. 1103.5 Flood hazard areas, additions are characterized as “structurally interconnected” (meaning structurally part of the base building) and “not structurally interconnected” (meaning the addition is, in effect, a separate building). Starting with the 8th Edition (2023), both Sec. 502.2 [Additions] Flood hazard areas, and Sec. 1103.5 [Additions that are structurally connected] have specific provision that apply to additions that do not constitute Substantial Improvement. FDEM considers “shall not create” to mean the addition must not create any new nonconformity. Examples of this would be if the area under the addition is enclosed, but the enclosure does not match the enclosure requirements of the base building depending on flood zone (e.g., flood openings, materials, breakaway walls) and if the utilities and equipment that serve the addition do not match the elevation of the floor. FDEM considers “shall not extend” to mean the addition must not make any existing nonconformity worse (the same meaning suggested by use of “not less conforming”). One example of how an addition, especially a non-substantial improvement addition, might make a nonconformity worse is if the base building in Zone V has a column or pile foundation and the addition does not have a Zone V compatible foundation (and match the elevation of the base building). FEMA P-758 and other FEMA publications are written based on NFIP minimum requirements and FEMA interpretations at the time a publication was written. FEMA no longer uses “pre-/post-FIRM” to describe requirements for construction. Those terms are used for NFIP flood insurance purposes. Using them in regulatory context can lead to misapplication of the requirements.