Project Basis Gate
This article explains the 2024 IMC model-code path. Before project use, confirm the adopted code edition, local amendments, controlling administrative provisions, permit-application date, and current AHJ procedures. The locally adopted requirements control.
Section 101 is the first decision gate on every project: which code governs this scope? Getting it wrong before drawings start means every downstream compliance decision may be built on the wrong foundation.
Plain English:
IMC covers the design, installation, maintenance, alteration, and inspection of mechanical systems in buildings: HVAC, exhaust, ventilation, refrigeration, and related systems.
Maintenance is in scope (101.1): Installed systems must be maintained in safe operating condition - the IMC is not just a construction code. Owners and operators have ongoing obligations.
Fuel gas systems? Not here - all gas piping, gas-fired appliances, and venting follow the IFGC. If fuel gas and HVAC appear on the same permit scope, the gas portion is routed to a separate IFGC permit unless the AHJ accepts a combined set.
1-2 family homes (under 3 stories): These can follow either the IMC or the IRC. The choice affects which requirements govern - confirm the applicable code with the AHJ before the first mechanical drawing is issued.
Appendices only apply if the jurisdiction specifically adopts them by ordinance. Do not apply an appendix requirement unless you can cite the jurisdiction's adoption in writing.
Purpose (101.3): Safety, health, public welfare, and property protection. The code exists to protect people in and around buildings - not to create administrative burden. Every requirement connects back to one of those four purposes.
On Plans: Why It Matters in Design & Construction:
Code basis on M-001 is not optional. Stating the applicable IMC edition, the IFGC reference (if gas is in scope), and the IRC/IMC election for residential establishes the reviewer's expectations from the first page.
Confirm scope before drawing production. A project team that discovers mid-design that the scope is split between IMC and IFGC adds a permit routing problem to an already-busy schedule.
Appendices need explicit adoption confirmation. Applying an appendix requirement that the jurisdiction hasn't adopted generates an AHJ question. Confirming it up front eliminates that friction.
Code Path: What to Note on M-001
State the applicable code edition and the jurisdiction's adoption date.
Reference IFGC for gas scope if applicable; note IRC path for 1-2 family homes under 3 stories.
Confirm which appendices are locally adopted (list them or note 'none adopted').
Check: Before You Start
Confirm with the AHJ: IMC or IRC for this project scope?
Verify the jurisdiction's adopted IMC edition and any local amendments.
Confirm fuel gas scope routes to IFGC, not IMC.
Review Risk:
Don't assume the IMC covers fuel gas piping - that's the IFGC.
Don't overlook the IRC option for 1-2 family homes under 3 stories.
Don't apply appendices without confirming local adoption.
Field Tip:
Before you start a project, always confirm with the AHJ:
"Are we under the IMC or IRC for this scope?"
That 2-minute check can save you 2 weeks of redlines.
Masterbuild QA Lens
Scope determines what goes on which permit. Before the set is issued, confirm: does the fuel gas scope route to IFGC, does process equipment fall under IMC or a specialty code, and does the jurisdiction specifically adopt any appendices. Scope disagreements with the AHJ cost more time than they save.
Drawing / Submittal Check
M-001 must state: IMC edition adopted by the jurisdiction, IFGC reference for gas scope (if any), IRC vs IMC election for residential (if applicable), and any adopted appendices. These four items confirm scope to the reviewer before they open the first mechanical sheet.
Common Review Risk
The most common scope conflict: a mixed project where HVAC and gas-fired equipment appear on the same mechanical sheets, but the gas piping scope belongs under the IFGC. The AHJ will hold the mechanical permit until the gas scope is explicitly separated and routed to its own permit. Fix it on M-001, not in response to a plan review comment.
When To Escalate
Escalate when an AHJ rules that your project scope falls outside the IMC - such as redirecting fuel-gas systems to the IFGC or low-rise residential to the IRC - and the design team hasn't built those different compliance paths into the drawings.
Ventilation Coordination
IMC 101 scope projects: confirm the outdoor air system is classified under IMC (not IFGC or other code) before routing the permit. For projects in jurisdictions with supplemental ventilation requirements (school IAQ mandates, healthcare ventilation standards), confirm those requirements are addressed on M-001 in addition to the IMC minimums.