/ Field knowledge · IMC 102
“Grandfathered” is not a drawing note.
IMC 102: lawfully installed systems can stay. Additions, repairs, and replacements must meet today’s code without making the overall system less safe than before. Occupancy change is not a note — it is a confirmation with the code official.
Educational 2024 IMC 102. Confirm adopted edition. Distinct from 105 permits. “Grandfathered” is not a drawing note.
- 102.1 conflicts: specific requirement over general; where IMC sections conflict, the most restrictive governs.
- 102.2 existing systems: lawfully installed systems can stay; additions / repairs / replacements must meet today’s code without making the overall system less safe than before.
- 102.3 maintenance: all systems — new and existing — must be maintained in safe, sanitary, and working order. Maintenance follows ASHRAE/ACCA/ANSI 180.
- 102.4 change in occupancy: any change in building use or occupancy must be confirmed with the code official — new occupancy may require mechanical upgrades to current code.
- 102.5 referenced standards: Chapter 15 standards apply at the edition listed, unless they conflict with an express IMC requirement — the IMC governs.
- 102.6 gaps: if the IMC doesn’t cover it, the code official determines the applicable requirements using nationally recognized standards, test data, or technical opinion. Other laws still apply independently.
M-001: new vs existing-to-remain, prior use vs proposed use, Chapter 15 standard and edition. Confirm with the AHJ whether the scope disturbs existing conditions and triggers upgrade. Skipping that confirmation is a top cause of plan-review delay.
Existing-to-remain, no map
The reviewer cannot tell which portions are new vs remaining, or the alteration triggers a full upgrade that was not budgeted. Identify every scope element touching existing systems before submittal.
Source: DCT 102 · official: 104 · permits: 105 · documents: 106.
What to send
What is existing-to-remain, what is new, and whether occupancy is changing.
If the TI assumes the old AHU is grandfathered
Send the existing-vs-new map. Masterbuild will say whether 102.2 even lets that unit stay — or the occupancy change already triggered current code.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
Masterbuild provides engineering services under a written scope. Nothing on this page is project-specific engineering advice, a code interpretation for your project, or a representation about permit approval. Confirm the adopted edition. Recirculation numbers below are 2024 IMC 510.1.3 education from Daily Code Talk — not a dust-collector selection. This page is not an air-quality permit.