CEBC · California Existing Building Code
Do repairs in flood hazard areas trigger substantial improvement requirements?
If a repair in a mapped flood hazard area equals or exceeds **50%** of the building’s pre‑work market value — or follows a condition of **substantial damage** — the CEBC requires the building be upgraded to the new‑construction flood standards in **§ 1612** (CBC) or **§ R306** (CRC). The local code official determines whether the work is “substantial improvement” and enforces the requirement under **§ 401.3**.
Last reviewed: July 6, 2026
What the code requires — plain English
In the California Existing Building Code, § 401.3 says that in flood hazard areas any repairs that constitute substantial improvement must make the building comply with the flood-design rules for new construction in § 1612 of the California Building Code (or § R306 of the California Residential Code where applicable). § 401.3 is the controlling CEBC mandate.
If a repair in a mapped flood hazard area meets the code’s definition of “substantial improvement,” the building must be upgraded to the flood‑resistant construction requirements that apply to new buildings.
Requirements in detail
- The trigger: a repair “constitutes substantial improvement” (see definition below). When that trigger is met, the building must be brought into compliance with the flood provisions for new construction in § 1612 (CBC) or § R306 (CRC). § 401.3 requires this.
- Who decides: the code official must determine whether proposed repairs are “substantial improvement” (see the administrative rule in § 104.3.1). If the official determines the work is substantial, the flood-design requirements apply.
- Variances/modifications: for existing buildings in flood hazard areas, the code official’s ability to modify flood-resistance provisions is tightly limited and subject to specific findings and written notice (see § 104.2.4.1).
Key defined term and threshold (bolded on first mention)
- Substantial improvement — any repair, alteration, addition or improvement of a building or structure the cost of which equals or exceeds 50 percent of the market value of the structure before the improvement or repair is started. If a structure has sustained substantial damage, any repairs are considered substantial improvement regardless of the repair cost.
Decision‑relevant dimensions (quick reference table)
| Decision dimension | Value / threshold | Consequence if threshold met | Code reference |
|---|---|---|---|
| Definition of “substantial improvement” | 50% of market value (cost of work ≥ 50%) | Building must meet flood-design requirements for new construction | § 401.3; definition text |
| Repairs after substantial damage | Any repair after a building has sustained substantial damage | Repairs are treated as substantial improvement regardless of cost | Definition of “substantial damage/substantial improvement” |
| Required standard when trigger met | New-construction flood requirements | Must follow § 1612 (CBC) or § R306 (CRC) as applicable | § 401.3 referencing § 1612 / § R306 |
| Administrative determination | Code official determines whether work “constitutes substantial improvement” | Code official enforces § 1612 / § R306 when determination made | § 104.3.1 (administration) |
| Modification/variance limits | Strict findings required before any flood-resistance modification | Very limited ability to lower flood requirements; written notice required | § 104.2.4.1 (modifications in flood hazard areas) |
Exceptions & special cases
- Historic structures: the definition of substantial improvement in the CEBC/CRC excludes certain alterations of historic structures where the alteration will not preclude continued designation as historic. Check the specific definition text for the historic exception.
- Health/safety corrections: projects required to correct existing health, sanitary, or safety code violations that are the minimum necessary to assure safe living conditions are excluded from the substantial‑improvement measure in some code definitions. Consult the applicable definition text.
- Administrative discretion: the code official has explicit authority to determine whether proposed work is substantial improvement and may require supporting documentation (e.g., cost estimates, market value). See § 104.3.1.
- Variances are limited: modifications to flood-resistance requirements for existing buildings that are substantially improved can be granted only after strict findings and with written notice to the applicant under § 104.2.4.1.
Common mistakes
- Assuming every repair in a floodplain automatically triggers full flood upgrades. Only repairs that meet the substantial improvement definition (or follow a repair after substantial damage) do so. § 401.3 is the specific trigger.
- Forgetting the 50% threshold or the “substantial damage” clause — both change whether the building must be upgraded. The CEBC definition is the baseline; do not rely on memory alone.
- Not involving the code official early. The building official must determine whether work is substantial (see § 104.3.1) and may require documentation. Getting that determination up front avoids surprises.
- Assuming local exceptions or variances are readily available. The CEBC limits modifications for flood hazard areas and requires written findings and notice if granted under § 104.2.4.1.
- Relying on forms of the Residential Code when the commercial/other CEBC language controls — § 401.3 points you to § 1612 (CBC) or § R306 (CRC) “as applicable,” so apply the correct code to your building type.
Worked example — numeric scenario
- Situation: A non‑residential building in an SFHA (Special Flood Hazard Area) has a pre‑damage market value of $200,000. Flood repair cost estimate = $110,000.
- Step 1 — Apply the threshold: $110,000 is 55% of $200,000 (110,000 ÷ 200,000 = 0.55), which exceeds the 50% substantial‑improvement threshold.
- Step 2 — Code consequence: Because the repair constitutes substantial improvement, § 401.3 requires that the building comply with the flood-design requirements for new construction in § 1612 (CBC) (or § R306 if residential). That will typically require elevating or flood‑proofing elements as required by § 1612/ASCE 24.
- Step 3 — Administrative action: The permit application must demonstrate compliance; the code official will make the determination and may require plans and calculations per § 104.3.1.
If instead the repair cost were $90,000 (45% of market value), then under the CEBC definition the work would not meet the substantial‑improvement threshold and the full new‑construction flood upgrades would not be required by § 401.3 — unless the building had previously sustained substantial damage or the code official’s determination or other provisions change the outcome.
Related provisions (CEBC / referenced codes)
- § 401.3 (Flood hazard areas — repairs that are substantial improvement must comply with § 1612 or § R306)
- § 401.2 (General repair compliance — repairs must not make the building less complying)
- § 104.3.1 (Determination of substantially improved or substantially damaged existing buildings and structures in flood hazard areas — administrative role)
- § 104.2.4.1 (Modifications in flood hazard areas — strict findings and notice required)
- § 1612 (California Building Code — flood loads and flood‑resistant construction for new construction / substantial improvement)
- § R306 (California Residential Code — flood‑resistant construction for substantial improvement/repair of substantial damage)
- CEBC definitions: Substantial improvement and substantial damage (definition text and thresholds) — see CEBC definitions used in Chapter 2 and related sections.
Code references
Grounded in the retrieved California Existing Building Code — click a citation to read the verbatim passage:
CEBC § 105.2 High relevance — show source text
401 A .2 Compliance. The work shall not make the building less complying than it was before the repair was undertaken. Work on nondamaged components that is necessary for the required repair of damaged components shall be considered part of the repair and shall not be subject to requirements for alterations.
401 A .3 Flood hazard areas. In flood hazard areas, repairs that constitute substantial improvement shall require that the building comply with Section 1612 A of the California Building Code .
SECTION 402 A —BUILDING ELEMENTS AND MATERIALS
402 A .1 Glass replacement. The installation or replacement of glass shall be as required for new installations in accordance with the California Building Code.
SECTION 403 A —FIRE PROTECTION
403 A .1 General. Fire protection shall comply with the California Building Standards Code.
SECTION 404 A —MEANS OF EGRESS
404 A .1 General. Repairs shall be done in a manner that maintains the level of protection provided for the means of egress.
SECTION 405 A —STRUCTURAL
405 A .1 General. Structural damage shall be repaired in compliance with this section and Section 401 A .2.
Exception: Routine maintenance required by Chapter 3A, ordinary repairs exempt from permit in accordance with California Building Code Section 105.2, and abatement of wear due to normal service conditions shall not be subject to the requirements for repairs in this section.
405 A .1.1 Structural concrete. Repair of structural concrete shall be permitted to comply with ACI 562 Section 1.7, except where Section 405.2.2, 405.2.3 or 405.2.4.1 requires compliance with Section 304.3.
405 A .2 Repairs to damaged buildings. Repairs to damaged buildings shall comply with this section.
405 A .2.1 Repairs for less than substantial structural damage. Unless otherwise required by this section, for damage less than substantial structural damage, the damaged elements shall be permitted to be restored to their predamage condition. New struc- tural members and connections used for this repair shall comply with the detailing provisions of this code for new buildings of similar structure, purpose and location.
405 A .2.1.1 Snow damage. Structural components whose damage was caused by or related to snow load effects shall be repaired, replaced or altered to satisfy the requirements of Section 1608 of the California Building Code .
405 A .2.2 Disproportionate earthquake damage. A building assigned to Seismic Design Category D, E or F that has sustained disproportionate earthquake damage shall be subject to the requirements for buildings with substantial structural damage to vertical elements of the lateral force-resisting system.
CEBC § 1.11. High relevance — show source text
The state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.
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4 A REPAIRS
User notes:
About this chapter: Chapter 4A governs the repair of existing buildings regulated by the Department of Health Care Access and Information/Office of Statewide Hospital Planning and Development, which include hospitals and correctional treatment centers [applications listed in Section 1.10.1 (OSHPD 1)].
SECTION 401 A —GENERAL
401 A .1 Scope. Repairs shall comply with the requirements of this chapter. The provisions of this chapter shall apply to existing structures for applications listed in Section 1.10.1 [OSHPD 1] regulated by the Department of Health Care Access and Information/Office of Statewide Hospital Planning and Development (OSHPD).
401 A .1.1 Bleachers, folding and telescopic seating and grandstands. Repairs to existing bleachers, folding and telescopic seating and grandstands shall comply with ICC 300.
401 A .2 Compliance. The work shall not make the building less complying than it was before the repair was undertaken. Work on nondamaged components that is necessary for the required repair of damaged components shall be considered part of the repair and shall not be subject to requirements for alterations.
401 A .3 Flood hazard areas. In flood hazard areas, repairs that constitute substantial improvement shall require that the building comply with Section 1612 A of the California Building Code .
SECTION 402 A —BUILDING ELEMENTS AND MATERIALS
402 A .1 Glass replacement. The installation or replacement of glass shall be as required for new installations in accordance with the California Building Code.
SECTION 403 A —FIRE PROTECTION
403 A .1 General. Fire protection shall comply with the California Building Standards Code.
SECTION 404 A —MEANS OF EGRESS
404 A .1 General. Repairs shall be done in a manner that maintains the level of protection provided for the means of egress.
SECTION 405 A —STRUCTURAL
405 A .1 General. Structural damage shall be repaired in compliance with this section and Section 401 A .2.
Exception: Routine maintenance required by Chapter 3A, ordinary repairs exempt from permit in accordance with California Building Code Section 105.2, and abatement of wear due to normal service conditions shall not be subject to the requirements for repairs in this section.
CEBC § 105.2 High relevance — show source text
SECTION G103—APPLICABILITY
G103.1 General. This appendix, in conjunction with this code, provides minimum requirements for development located in flood hazard areas, including:
The subdivision of land.
Site improvements and installation of utilities.
Placement and replacement of manufactured homes.
Placement of recreational vehicles.
New construction and repair, reconstruction, rehabilitation or additions to new construction.
Substantial improvement of existing buildings and structures, including restoration after damage.
Installation of tanks.
Temporary structures.
Temporary or permanent storage, utility and miscellaneous Group U buildings and structures.
Certain building work exempt from permit under Section 105.2 and other buildings and development activities.
G103.2 Establishment of flood hazard areas. Flood hazard areas are established in Section 1612.3 of this code, adopted by the applicable governing authority on [ INSERT DATE ] .
SECTION G104—POWERS AND DUTIES
G104.1 Permit applications. All applications for permits shall comply with the following:
The floodplain administrator shall review all permit applications to determine whether proposed development is located in flood hazard areas established in Section G103.2.
Where a proposed development site is in a flood hazard area, all development to which this appendix is applicable as specified in Section G103.1 shall be designed and constructed with methods, practices and materials that minimize flood damage and that are in accordance with this code and ASCE 24.
G104.2 Other permits. It shall be the responsibility of the floodplain administrator to ensure that approval of a proposed development shall not be given until proof that necessary permits have been granted by federal or state agencies having jurisdiction over such development.
G104.3 Determination of design flood elevations. If design flood elevations are not specified, the floodplain administrator is authorized to require the applicant to meet one of the following:
- Obtain, review and reasonably utilize data available from a federal, state or other source.
- Determine the design flood elevation in accordance with accepted hydrologic and hydraulic engineering techniques. Such analyses shall be performed and sealed by a registered design professional. Studies, analyses and computations shall be submitted in sufficient detail to allow review and approval by the floodplain administrator. The accuracy of data submitted for such determination shall be the responsibility of the applicant.
G104.4 Activities in riverine flood hazard areas. In riverine flood hazard areas where design flood elevations are specified but floodways have not been designated, the floodplain administrator shall not permit any new construction, substantial improvement or other development, including fill, unless the applicant submits an engineering analysis prepared by a registered design professional, demonstrating that the cumulative effect of the proposed development, when combined with all other existing and anticipated flood hazard area encroachment, will not increase the design flood elevation more than 1 foot (305 mm) at any point within the community.
G104.5 Floodway encroachment. Prior to issuing a permit for any floodway encroachment, including fill, new construction, substantial improvements and other development or land-disturbing activity, the floodplain administrator shall require submission of a certification, prepared by a registered design professional, along with supporting technical data, demonstrating that such development will not cause any increase of the base flood level.
G104.5.1 Floodway revisions. A floodway encroachment that increases the level of the base flood is authorized if the applicant has applied for a conditional Flood Insurance Rate Map (FIRM) revision and has received the approval of the Federal E
CEBC § 401.3 High relevance — show source text
[BS] 401.3 Flood hazard areas. In flood hazard areas, repairs that constitute substantial improvement shall require that the building comply with Section 1612 of the California Building Code, or Section R306 of the California Residential Code, as applicable.
SECTION 402—BUILDING ELEMENTS AND MATERIALS
402.1 Glazing in hazardous locations. Replacement glazing in hazardous locations shall comply with the safety glazing requirements of the California Building Code or California Residential Code as applicable.
Exception: Glass block walls, louvered windows and jalousies repaired with like materials.
402.2 Existing materials. [HCD] Existing materials shall comply with Section 302.3.
402.3 New and replacement materials. [HCD & HCD 2] New and replacement materials used for repairs shall comply with Section 302.4.
SECTION 403—FIRE PROTECTION
403.1 General. Repairs shall be done in a manner that maintains the level of fire protection provided.
SECTION 404—MEANS OF EGRESS
404.1 General. Repairs shall be done in a manner that maintains the level of protection provided for the means of egress.
SECTION 405—STRUCTURAL
[BS] 405.1 General. Structural damage shall be repaired in compliance with this section and Section 401.2.
405.1.1 Structural concrete. Repair of structural concrete shall be permitted to comply with ACI 562 Section 1.7, except where Section 405.2.2, 405.2.3 or 405.2.4.1 requires compliance with Section 304.3.
[BS] 405.2 Repairs to damaged buildings. Repairs to damaged buildings shall comply with this section.
[BS] 405.2.1 Repairs for less than substantial structural damage. Unless otherwise required by this section, for damage less than substantial structural damage, the damaged elements shall be permitted to be restored to their predamage condition.
[BS] 405.2.1.1 Snow damage. Structural components whose damage was caused by or related to snow load effects shall be repaired, replaced or altered to satisfy the requirements of Section 1608 of the California Building Code .
[BS] 405.2.2 Disproportionate earthquake damage. A building assigned to Seismic Design Category D, E or F that has sustained disproportionate earthquake damage shall be subject to the requirements for buildings with substantial structural damage to vertical elements of the lateral force-resisting system.
[BS] 405.2.3 Substantial structural damage to vertical elements of the lateral force-resisting system. A building that has sustained substantial structural damage to the vertical elements of its lateral force-resisting system shall be evaluated in accordance with Section 405.2.3.1, and either repaired in accordance with Section 405.2.3.2 or repaired and retrofitted in accordance with Section 405.2.3.3, depending on the results of the evaluation.
Exceptions:
- Buildings assigned to Seismic Design Category A, B or C whose substantial structural damage was not caused by earthquake need not be evaluated or retrofitted for load combinations that include earthquake effects.
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REPAIRS
CEBC § 401.1 High relevance — show source text
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4 REPAIRS
User notes:
About this chapter: Chapter 4 provides requirements for repairs of existing buildings. The provisions define conditions under which repairs may be made using materials and methods like those of the original construction or the extent to which repairs must comply with requirements for new buildings.
SECTION 401—GENERAL
401.1 Scope. R epairs shall comply with the requirements of this chapter. Repairs to historic buildings and structures shall comply with Part 8, Title 24, C.C.R. [OSHPD 1R, 2, 4 & 5] Repairs to historic buildings not adopted by OSHPD. Repairs shall comply with the requirements in the California Building Code, Sections 1224.2, 1225.2, 1226.2, 1227.2 and 1228.2 for functional requirements as applicable.
401.1.1 Bleachers, folding and telescopic seating and grandstands. Repairs to existing bleachers, folding and telescopic seating and grandstands shall comply with ICC 300.
401.1.2 Scope. [BSC] For state-owned buildings, including those owned by the University of California and the California State University and the Judicial Council, the requirements of Sections 405.2.1 and 405.2.3 are replaced by the requirements of Sections 317 through 322.
401.2 Compliance. The work shall not make the building less complying than it was before the repair was undertaken. Work on nondamaged components that is necessary for the required repair of damaged components shall be considered part of the repair and shall not be subject to requirements for alterations.
[BS] 401.3 Flood hazard areas. In flood hazard areas, repairs that constitute substantial improvement shall require that the building comply with Section 1612 of the California Building Code, or Section R306 of the California Residential Code, as applicable.
SECTION 402—BUILDING ELEMENTS AND MATERIALS
402.1 Glazing in hazardous locations. Replacement glazing in hazardous locations shall comply with the safety glazing requirements of the California Building Code or California Residential Code as applicable.
Exception: Glass block walls, louvered windows and jalousies repaired with like materials.
402.2 Existing materials. [HCD] Existing materials shall comply with Section 302.3.
402.3 New and replacement materials. [HCD & HCD 2] New and replacement materials used for repairs shall comply with Section 302.4.
SECTION 403—FIRE PROTECTION
403.1 General. Repairs shall be done in a manner that maintains the level of fire protection provided.
SECTION 404—MEANS OF EGRESS
404.1 General. Repairs shall be done in a manner that maintains the level of protection provided for the means of egress.
SECTION 405—STRUCTURAL
[BS] 405.1 General. Structural damage shall be repaired in compliance with this section and Section 401.2.
405.1.1 Structural concrete. Repair of structural concrete shall be permitted to comply with ACI 562 Section 1.7, except where Section 405.2.2, 405.2.3 or 405.2.4.1 requires compliance with Section 304.3.
CEBC § 1.1 High relevance — show source text
Exception: In-filling of floor openings and nonoccupiable appendages such as elevator and exit stairway shafts shall be permitted beyond that permitted by the California Building Code.
502 A .1.1 Risk category assignment. Where the addition and the existing building have different occupancies, the risk category of each existing and added occupancy shall be determined in accordance with Section 1604 A .5.1 of the California Building Code . Where application of that section results in a higher risk category for the existing building compared with the risk category for the existing building before the addition, such a change shall be considered a change of occupancy and shall comply with Section 506 A of this code. Where application of that section results in a higher risk category for the addition compared with the risk category for the addition by itself, the addition and any systems in the existing building required to serve the addition shall comply with the requirements of the California Building Code for new construction for the higher risk category.
502 A .1.2 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 with regard to accessibility, structural strength, supports and attachments for nonstructural components, fire safety, means of egress or the capacity of mechanical, plumbing or electrical systems.
Exception: Nonconforming supports and attachments for nonstructural components that serve the addition from within the existing building need not be altered to comply with California Building Code Section 1613 A unless the components are part of the addition’s life-safety system or are required to serve an addition assigned to Risk Category IV.
502 A .2 Flood hazard areas. For buildings and structures in flood hazard areas established in California Building Code, Section 1612 A .3, any addition that constitutes substantial improvement of the existing structure , as defined in Chapter 2, shall comply with the flood design requirements for new construction, and all aspects of the existing structure shall be brought into compliance with
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PRESCRIPTIVE COMPLIANCE METHOD
the requirements for new construction for flood design. For new foundations, foundations raised or extended upward, and replacement foundations, the foundations shall be in compliance with the requirements for new construction for flood design.
For buildings and structures in flood hazard areas established in California Building Code, Section 1612 A .3, any additions that do not constitute substantial improvement of the existing structure , as defined in Chapter 2, are not required to comply with the flood design requirements for new construction, provided that both of the following apply:
- The addition shall not create or extend a nonconformity of the existing building or structure with the flood-resistant construction requirements.
- The lowest floor of the addition shall be at or above the lower of the lowest floor of the existing building or structure or the lowest floor elevation required in Section 1612 A of the California Building Code .
502 A .3 Existing structural elements carrying gravity load. Any existing gravity load-carrying structural element for which an addition and its related alterations cause an increase in design dead, live or snow load, including snow drift effects, of more than 5 percent shall be replaced or altered as needed to carry the gravity loads required by the California Building Code for new structures.
CEBC § 104.2.4.1 High relevance — show source text
[A] 104.2.4.1 Flood hazard areas. For existing buildings located in flood hazard areas for which repairs, alterations and additions constitute substantial improvement, the code official shall not grant modifications to provisions related to flood resistance unless a determination is made that:
The applicant has presented good and sufficient cause that the unique characteristics of the size, configuration or topography of the site render compliance with the flood-resistant construction provisions inappropriate.
Failure to grant the modification would result in exceptional hardship.
The granting of the modification will not result in increased flood heights, additional threats to public safety or extraordinary public expense; create nuisances; cause fraud on or victimization of the public; or conflict with existing laws or ordinances.
The modification is the minimum necessary to afford relief, considering the flood hazard.
A written notice will be provided to the applicant specifying, if applicable, the difference between the design flood elevation and the elevation to which the building is to be built, stating that the cost of flood insurance will be
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ADMINISTRATION
commensurate with the increased risk resulting from the reduced floor elevation and that construction below the design flood elevation increases risks to life and property.
[A] 104.3 Applications and permits. The code official shall receive applications, review construction documents, issue permits, inspect the premises for which such permits have been issued and enforce compliance with the provisions of this code.
[A] 104.3.1 Determination of substantially improved or substantially damaged existing buildings and structures in flood hazard areas. For applications for reconstruction, rehabilitation, repair, alteration, addition or other improvement of existing buildings or structures located in flood hazard areas, the code official shall determine where the proposed work constitutes substantial improvement or repair of substantial damage. Where the code official determines that the proposed work constitutes substantial improvement or repair of substantial damage, and where required by this code, the code official shall require the building to meet the requirements of Section 1612 of the California Building Code, or Section R306 of the California Residential Code, as applicable.
[A] 104.3.2 Preliminary meeting. When requested by the permit applicant or the code official, the code official shall meet with the permit applicant prior to the application for a construction permit to discuss plans for the proposed work or change of occupancy in order to establish the specific applicability of the provisions of this code.
Exception: Repairs and Level 1 alterations.
[A] 104.3.3 Building evaluation. The code official is authorized to require an existing building to be investigated and evaluated by a registered design professional based on the circumstances agreed on at the preliminary meeting. The design professional shall notify the code official if any potential noncompliance with the provisions of this code is identified.
[A] 104.4 Right of entry. Where it is necessary to make an inspection to enforce the provisions of this code, or where the code official has reasonable cause to believe that there exists in a structure or on any premises a condition that is contrary to or in violation of this code that makes the structure or premises unsafe, dangerous or hazardous, the code official is authorized to enter the structure or premises at all reasonable times to inspect or to perform the duties imposed by this code. If such structure or premises is occupied, the code official shall present credentials to the occupant and request entry.
CRC § 8350 High relevance — show source text
FACILITIES OF THE CENTRAL VALLEY FLOOD PROTECTION PLAN. The facilities referenced herein include the facilities of State Plan of Flood Control and other flood management facilities in the Central Valley evaluated under the Central Valley Flood Protection Plan, which will be completed in 2012 and updated every 5 years thereafter. The facilities of State Plan of Flood Control include the state and federal flood control works (levees, weirs, channels and other features) of the Sacramento River Flood Control Project described in Water Code Section 8350, and flood control projects in the Sacramento River and San Joaquin River watersheds authorized pursuant to Article 2 (commencing with Water Code section 12648) of Chapter 2 of Part 6 of Division 6 for which the Central Valley Flood Protection Board or the Department of Water Resources has provided the assurances of nonfederal cooperation to the United States, and those facilities identified in Water Code Section 8361.
ROUTE TO THE EVACUATION LOCATION. The path through and along which occupants move from the habitable areas of a building or structure that are below the WSEL200 to the evacuation location.
SUBSTANTIAL DAMAGE. Damage of any origin sustained by a structure whereby the cost of restoring the structure to its before- damaged condition would equal or exceed 50 percent of the market value of the structure before the damage occurred.
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APPENDIX CK — AREAS PROTECTED BY THE FACILITIES OF THE CENTRAL VALLEY FLOOD PROTECTION PLAN
SUBSTANTIAL IMPROVEMENT. Any repair, reconstruction, rehabilitation, addition or improvement of a building or structure, the cost of which equals or exceeds 50 percent of the market value of the structure before the improvement or repair is started. If the structure has sustained damage, any repairs are considered substantial improvement regardless of the actual repair work performed. The term does not, however, include either:
1. Any project for improvement of a building required to correct existing health, sanitary or safety code violations identified by the building official and that area the minimum necessary to assure safe living conditions. 2. Any alteration of a historic structure provided that the alteration will not preclude the structure’s continued designation as a historic structure.
WSEL200. The water surface elevation (WSEL) of the 200-year flood event that is identified by the state when it identifies areas that receive protection from the facilities of the Central Valley Flood Protection Plan.
CK103 Structural stability. Portions of buildings and structures that support evacuation locations shall be designed, constructed, connected and anchored to resist flotation, collapse or permanent lateral movement resulting from the hydrostatic loads anticipated during conditions of flooding anticipated for the 200-year flood event.
Exception: When one flood vent (minimum) is provided on two opposite sides of the building or structure that comply with Figure CK103.
CEBC § 3-3 High relevance — show source text
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PROVISIONS FOR ALL COMPLIANCE METHODS
members added as part of the alteration shall comply with the California Building Code . This exception shall not apply to the following:
Alterations for accessibility required by the California Building Code, Chapter 11A.
Alterations that constitute substantial improvement in flood hazard areas, which shall comply with Sections 503.2, 701.3 or 1303.1.3.
Structural provisions of Section 304, Chapter 5 or to the structural provisions of Sections 706, 805 and 906.
301.3.1 Prescriptive compliance. Alterations, additions and changes of occupancy complying with Chapter 5 of this code in buildings complying with the California Fire Code shall be considered in compliance with the provisions of this code.
Exception: Hospital buildings removed from acute care service, skilled nursing facilities, intermediate-care facilities, correctional treatment centers and acute psychiatric hospitals [OSHPD 1R, 2, 4 and 5]. The provisions of adopted sections in Chapters 3 through 5 shall control the alteration, repair and change of occupancy or function of existing structures for applications listed in Section 1.10.1, 1.10.2, 1.10.4 and 1.10.5 regulated by the Department of Health Care Access and Information/Office of Statewide Hospital Planning and Development (OSHPD). Refer to Chapter 3A for services, systems and utilities that serve OSHPD 1 buildings.
301.3.2 Work area compliance method. A lterations, additions and changes of occupancy complying with the applicable requirements of Chapters 6 through 12 of this code shall be considered in compliance with the provisions of this code.
301.3.3 Performance compliance method. Alterations, additions and changes of occupancy complying with Chapter 13 of this code shall be considered in compliance with the provisions of this code.
Note: [HCD 1 & HCD 2] The provisions contained in Chapter 13 are not adopted by HCD, but may be available for adoption by a local ordinance. (See Section 1.1.11.)
301.4 Relocated or moved buildings. Relocated or moved buildings shall comply with the requirements of Chapter 14.
SECTION 302—GENERAL PROVISIONS
302.1 Dangerous conditions. The code official shall have the authority to require the elimination of conditions deemed dangerous.
302.1.1 Dangerous conditions. [BSC] Regardless of the extent of structural or nonstructural damage, the code official shall have the authority to require the elimination of conditions deemed dangerous.
302.2 Additional codes. Alterations, repairs, additions and changes of occupancy to, or relocation of, existing buildings and structures shall comply with the provisions for alterations, repairs, additions and changes of occupancy or relocation, respectively, in this code and the California Energy Code, California Fire Code, California Mechanical Code, California Plumbing Code, California Residential Code and California Electrical Code . Where provisions of the other codes conflict with provisions of this code, the provisions of this code shall take precedence.
CEBC § 1011.11 High relevance — show source text
2. Drift limits based on original design code shall be permitted to be used in lieu of the drift limits required by ASCE 7.
SECTION 503 A —ALTERATIONS
503 A .1 General. Alterations to any building or structure shall comply with the requirements of the California Building Code for new construction. Alterations shall be such that the existing building or structure is not less complying with the provisions of the Califor- nia Building Code than the existing building or structure was prior to the alteration.
Exceptions:
- An existing stairway shall not be required to comply with the requirements of Section 1011 of the California Building Code where the existing space and construction does not allow a reduction in pitch or slope.
- Handrails otherwise required to comply with Section 1011.11 of the California Building Code shall not be required to comply with the requirements of Section 1014.7 of the California Building Code regarding full extension of the handrails where such extensions would be hazardous because of plan configuration.
503 A .2 Flood hazard areas. For buildings and structures in flood hazard areas established in Section 1612 A .3 of the California Build- ing Code, any alteration that constitutes substantial improvement of the existing structure , as defined in Chapter 2, shall comply with the flood design requirements for new construction, and all aspects of the existing structure shall be brought into compliance with the requirements for new construction for flood design.
For buildings and structures in flood hazard areas established in Section 1612 A .3 of the California Building Code any alterations that do not constitute substantial improvement of the existing structure , as defined in Chapter 2, are not required to comply with the flood design requirements for new construction.
503 A .3 Existing structural elements carrying gravity load. Any existing gravity load-carrying structural element for which an alteration causes an increase in design dead, live or snow load, including snow drift effects, of more than 5 percent shall be replaced or altered as needed to carry the gravity loads required by the California Building Code for new structures. Any existing gravity loadcarrying structural element whose gravity load-carrying capacity is decreased as part of the alteration shall be shown to have the capacity to resist the applicable design dead, live and snow loads including snow drift effects required by the California Building Code for new structures.
503 A .4 Existing structural elements carrying lateral load. Except as permitted by Section 503 A .13, where the alteration increases design lateral loads, results in a prohibited structural irregularity as defined in the California Building Code, ASCE 7, or decreases the
2025 CALIFORNIA EXISTING BUILDING CODE 5A-5
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PRESCRIPTIVE COMPLIANCE METHOD
capacity of any existing lateral load-carrying structural element, the lateral force-resisting system of the altered building or structure shall meet the requirements of Section s 1609 A and 1613A of the California Building Code .
Exceptions: For incidental and minor alterations:
- Any existing lateral load-carrying structural element whose demand-capacity ratio with the alteration considered is not more than 10 percent greater than its demand-capacity ratio with the alteration ignored shall be permitted to remain unaltered.
CEBC § 3-35 High relevance — show source text
Exceptions:
Buildings where the structural members of walls, floors, ceilings and roofs are entirely of noncombustible materials or pressure-preservative-treated wood.
Where in addition to the requirements of Section R305.1, an approved method of protecting the foam plastic and structure from subterranean termite damage is used.
On the interior side of basement walls.
2025 CALIFORNIA RESIDENTIAL CODE 3-35
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BUILDING PLANNING
FIGURE R305.4—TERMITE INFESTATION PROBABILITY MAP
Note: Lines defining areas are approximate only. Local conditions may be more or less severe than indicated by the region classification.
SECTION R306—FLOOD-RESISTANT CONSTRUCTION
R306.1 General. Buildings and structures constructed in whole or in part in flood hazard areas established in Table R301.2, and substantial improvement and repair of substantial damage of buildings and structures located in whole or in part in flood hazard areas, shall be designed and constructed in accordance with the provisions contained in this section. Buildings and structures that are located in more than one flood hazard area, including A Zones, Coastal A Zones and V Zones, shall comply with the provisions associated with the most restrictive flood hazard area. Buildings and structures located in whole or in part in identified floodways shall be designed and constructed in accordance with ASCE 24.
R306.1.1 Alternative provisions. As an alternative to the requirements in Section R306, ASCE 24 is permitted subject to the limitations of this code and the limitations therein.
R306.1.2 Structural systems. Structural systems of buildings and structures shall be designed, connected and anchored to resist flotation, collapse or permanent lateral movement due to structural loads and stresses from flooding equal to the design flood elevation.
R306.1.3 Flood-resistant construction. Buildings and structures erected in areas prone to flooding shall be constructed by methods and practices that minimize flood damage.
R306.1.4 Establishing the design flood elevation. The design flood elevation shall be used to define flood hazard areas. At a minimum, the design flood elevation shall be the higher of the following:
- The base flood elevation at the depth of peak elevation of flooding, including wave height, that has a 1-percent (100-year flood) or greater chance of being equaled or exceeded in any given year.
- The elevation of the design flood associated with the area designated on a flood hazard map adopted by the community, or otherwise legally designated.
R306.1.4.1 Determination of design flood elevations. If design flood elevations are not specified, the building official is authorized to require the applicant to comply with either of the following:
- Obtain and reasonably use data available from a federal, state or other source.
- Determine the design flood elevation in accordance with accepted hydrologic and hydraulic engineering practices used to define special flood hazard areas. Determinations shall be undertaken by a registered design professional who shall document that the technical methods used reflect currently accepted engineering practice. Studies, analyses and computations shall be submitted in sufficient detail to allow thorough review and approval.
CEBC § 0.65 High relevance — show source text
2025 CALIFORNIA RESIDENTIAL CODE APPENDIX CK-3
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APPENDIX CK — AREAS PROTECTED BY THE FACILITIES OF THE CENTRAL VALLEY FLOOD PROTECTION PLAN
SUBSTANTIAL IMPROVEMENT. Any repair, reconstruction, rehabilitation, addition or improvement of a building or structure, the cost of which equals or exceeds 50 percent of the market value of the structure before the improvement or repair is started. If the structure has sustained damage, any repairs are considered substantial improvement regardless of the actual repair work performed. The term does not, however, include either:
1. Any project for improvement of a building required to correct existing health, sanitary or safety code violations identified by the building official and that area the minimum necessary to assure safe living conditions. 2. Any alteration of a historic structure provided that the alteration will not preclude the structure’s continued designation as a historic structure.
WSEL200. The water surface elevation (WSEL) of the 200-year flood event that is identified by the state when it identifies areas that receive protection from the facilities of the Central Valley Flood Protection Plan.
CK103 Structural stability. Portions of buildings and structures that support evacuation locations shall be designed, constructed, connected and anchored to resist flotation, collapse or permanent lateral movement resulting from the hydrostatic loads anticipated during conditions of flooding anticipated for the 200-year flood event.
Exception: When one flood vent (minimum) is provided on two opposite sides of the building or structure that comply with Figure CK103.
CK103.1 Determination of loads. Hydrostatic loads, based on the depth of water determined by the WSEL200 shall be determined in accordance with Chapter 5 of ASCE 7. Reduction of hydrostatic loads may be accomplished by allowing for the automatic entry and exit of floodwaters to minimize unbalanced loads. Such means shall be designed by a registered design professional and include, but are not limited to, openings, valves and panels designed to yield under load.
CK104 Evacuation Locations. An evacuation location and a route to the evacuation location shall be provided.
CK104.1 Route to evacuation location. A route shall be allowed through any number of intervening rooms or spaces. Doors along the route shall be openable without the use of a key, lock, special knowledge or effort.
CK104.2 minimum size requirements. Evacuation locations shall provide a minimum gross floor area of 7 square feet (0.65 m [2] ) per occupant, based on the occupant load of the portions of the building that are below WSEL200. The area provided shall be adequate to accommodate the occupant load of the upper levels as well as the anticipated occupant load from the area below the WSEL200.
CK105 Space within the building. If the evacuation location is a space within a building, the evacuation location shall be provided with a means for occupants to be evacuated out of the building specified in Section CK105.1, CK105.2 or CK105.3. The means for occupants to be evacuated out of the building shall address the mobility of the occupants.
Frequently asked questions
Do small repairs (like replacing drywall or carpet) trigger the rule?
No — routine, ordinary repairs that do not meet the substantial improvement threshold (cost < 50% of market value) generally do not trigger the § 401.3 flood upgrades. However, the code official makes the formal determination for permit review.
If a building was substantially damaged, does that change the rule?
Yes — if the structure has sustained substantial damage, the CEBC treats repairs as substantial improvement regardless of the repair cost, and the building must meet the new‑construction flood rules.
Which flood standard applies if my building is commercial?
When the trigger in § 401.3 is met for nonresidential or mixed‑use buildings, follow § 1612 (CBC) and ASCE 24 (flood‑resistant construction for new buildings). Residential buildings may instead use § R306 where applicable.
Can I get a variance from the flood requirements if my repair is substantial?
Variances or modifications are tightly constrained. § 104.2.4.1 sets strict findings and written‑notice requirements before any modification to flood‑resistance provisions may be granted. Expect a high bar.
Who should I talk to first on a repair project in a floodplain?
Contact your local building/floodplain official before preparing detailed bids. The code official determines whether the work is “substantial improvement” and can advise on required submittals under § 104.3.1.
More in California Existing Building Code
- Administration and Definitions (Scope, enforcement, code official duties, definitions)
- Provisions for All Compliance Methods (general requirements that apply to all compliance options; Chapter 3 / 3A)
- Seismic retrofit and evaluation (Appendix A and seismic provisions/sections for evaluation and retrofit)
- Referenced Standards and Appendices (Chapter 16 and Appendices A–E, Resource A)
- Repairs (Chapter 4 — repair-specific rules for materials, means of egress, structural, MEP, etc.)
- Alterations — Level 1, Level 2, Level 3 (technical requirements for each alteration level; Chapters 7–9)
- Change of Occupancy and Additions (requirements for occupancy changes and additions; Chapters 10–11)
- Compliance Methods — Prescriptive, Work Area, Performance (Chapters 5, 6–11, 13)
- Relocated Buildings (requirements for buildings moved or relocated; Chapter 14)
- Construction Safeguards (site safety, means of egress and life-safety during construction; Chapter 15)
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