2021 IMC and IFGC Chapter 1
Before a duct is hung or a gas line is run, someone has to settle three questions: which code applies here, what permission the job needs, and who signs off when it is done. Chapter 1 of the 2021 IMC and IFGC answers the second and third. Local law answers the first, and on the Gulf Coast that answer is not the same everywhere. The rest of this course teaches the 2021 IMC and IFGC, but the City of Houston enforces a different mechanical code, so this lesson begins there.
Two state sources we checked, the Texas State Law Library building codes guide (updated June 2026) and the Texas Municipal League building codes summary (July 2021), describe a statewide baseline for commercial building construction but name no statewide mechanical code. Cities adopt their codes by ordinance. The practical rule: ask the local code office which mechanical code and edition it enforces, and which amendments come with it.
Houston is the clear example. The city adopted the 2021 Uniform Mechanical Code (UMC) with Houston amendments, replacing the 2015 edition, effective in early January 2024. Three sources agree: an IAPMO press release from October 2023, a Green Builder Media report dated November 20, 2023, and the Houston Permitting Center's own published amendments, titled the Uniform City of Houston Mechanical Code. Houston has used the Uniform family of codes since 1985. A Houston plan review is written against UMC section numbers, not IMC numbers, so never quote an IMC section on a Houston comment without checking the UMC and the city amendments. Many other Texas cities use the IMC. Local adoption governs everywhere.
The state also licenses air conditioning and refrigeration contractors through the Texas Department of Licensing and Regulation (Occupations Code Chapter 1302; TDLR licensing summary, December 2025). A license says who may do the work. A permit says this particular job was reviewed and inspected. A contractor needs the first and the job needs the second.
IMC Section 101.2 covers the design, installation, maintenance, alteration, and inspection of permanent mechanical systems that control the environment inside buildings. Fuel gas piping, gas-fired appliances, and their venting belong to the IFGC, which is why this course pairs the two books. Detached one- and two-family dwellings and townhouses up to three stories may follow the IMC or the International Residential Code. Appendices apply only if the jurisdiction adopts them (101.2.1). When a general rule and a specific rule conflict, the specific one governs, and when two sections differ, the most restrictive governs (102.1).
A lawfully existing system may stay and stay in use (102.2). The owner is responsible for keeping it maintained and safe (102.3), with HVAC maintenance inspections per ASHRAE/ACCA/ANSI 180. New work is different. Additions, alterations, and repairs must meet the requirements for a new system, but the whole existing system need not be upgraded, provided the work does not make it unsafe, hazardous, or overloaded (102.4). A change in occupancy needs approval (102.5). Building and structural alterations follow the International Existing Building Code (102.2.1), and used equipment may be reused only after reconditioning, testing, and approval (105.5).
An owner, agent, or contractor who wants to erect, install, enlarge, alter, repair, remove, convert, or replace a mechanical system must first apply and obtain the permit (106.1). The IMC exempts a short list in 106.2: portable heating, ventilation, and cooling units, portable evaporative coolers, piping inside listed heating or cooling equipment, replacement of a minor part that does not change the equipment's approval, and portable fuel cell appliances not connected to fixed piping or the power grid. It also exempts a self-contained refrigeration system with 10 pounds of refrigerant or less, or motors of 1 horsepower or less. The IFGC exempts only two things: portable heating appliances and minor component replacement (IFGC 106.2). An exemption never authorizes work that violates the code.
Two flexibility provisions matter in rehab. Where equipment must be replaced or repaired in an emergency, the permit application is due within the next working business day (106.1 exception). And a facility that regularly employs qualified tradespersons may get an annual permit for alterations to approved systems, provided it keeps detailed records (106.1.1, 106.1.2).
The application goes on the official form with the fee. It carries a general description and location of the work, the proposed occupancy, and the signature of the owner or agent (106.3). Construction documents are submitted in two or more sets or digitally, drawn to scale, and prepared by a registered design professional where state law requires one (110.1). For buildings over two stories they must show where mechanical penetrations occur and how fire-resistance and fireblocking are maintained. The official can waive documents when review is unnecessary. Fees must be paid or the permit is not valid (109.1), and starting work before the permit draws an added fee (109.4).
Approved documents are stamped APPROVED, and work must follow them (106.4.1). A permit for part of a system may be issued early, but the holder proceeds at their own risk. A permit never authorizes a violation, and the official can still require correction of errors afterward (106.4.2). The official can suspend or revoke a permit issued in error (106.4.5), and the permit or a copy stays on site until the project is complete (106.4.7).
Worked example. A permit for a rooftop unit replacement at a community center is issued on March 1, 2027, and the fee is $300 (illustrative; the local schedule governs). Work must start within 180 days, so the deadline is August 28, 2027. If the unit is delayed, the owner requests one extension in writing before that date: up to 180 more days for $150, half the fee, and no second extension is allowed. If the permit lapses instead, a new permit is needed. It costs $150 if the plans are unchanged and the lapse is under a year, and the full $300 if the plans changed.
Work must remain visible and accessible until approved (108.1). The permit holder schedules the inspections and provides access (108.2, 108.2.2). Three are named. The underground inspection comes after the trench is excavated and bedded and the piping is installed, and before backfill. The rough-in inspection comes after the roof, framing, fireblocking, and bracing are in place and all ducting and other concealed components are complete, and before wall or ceiling membranes go up. The final inspection comes when the system is complete. Ground-source heat pump loops tested under Section 1210.10 may be backfilled before inspection. The official may add other inspections (108.2.1) and accept written agency reports (104.3). No work proceeds past an inspection point without approval, and a failed portion may not be covered until the official authorizes it (108.2.3).
In the field
In January an older homeowner's furnace fails, and the crew swaps it the same day. The emergency exception lets the heat stay on, but it does not erase the paperwork: the permit application is due by the next working business day, and the inspection request must be filed within 48 hours and before any part of the new unit is concealed. On a rehab job GCHS writes both deadlines on the work order. Remember also that Houston follows the UMC, so confirm the local timing rule before relying on these IMC numbers.
Mechanical systems are tested as the code requires, and the tests are made by the permit holder and observed by the code official. The permit holder furnishes the apparatus, material, and labor (108.3, 108.3.2). New systems, and altered, extended, or repaired parts of old ones, are tested to disclose leaks and defects. Work that fails is corrected and resubmitted (108.3.3). The IFGC works the same way in its Section 112. When the prescribed tests and inspections show the work complies, the official issues a notice of approval, which can later be revoked if it was issued in error (111.1, 111.2). No one may connect a utility, fuel, or power source to a system that needed a permit until the official authorizes it, although a temporary connection for testing can be allowed (112.1, 112.2). Lesson 14 collects the tests.
Where strict compliance is impractical, the official may grant a modification for an individual case if the intent of the code is met and health, life, and fire safety are not lessened (105.1). Alternative materials, designs, and methods must be approved if the official finds them not less than equivalent in quality, strength, effectiveness, fire resistance, durability, and safety, and a refusal must be given in writing (105.2). Tests the official requires as evidence of compliance are at no expense to the jurisdiction (105.3). A stop work order must be in writing and state the reason and the conditions for resuming, although in an emergency no written notice is needed first (113.2, 113.3). Sections 114 and 115 cover appeals and violations, and penalty amounts are left for each city to fill in.
1. A plan reviewer for a Houston permit writes a correction citing IMC Section 306.3 for an attic furnace. What is wrong with the comment?
2. Under IMC Section 101.2, which code regulates fuel gas piping, gas-fired appliances, and their venting?
3. Which of these mechanical installations is exempt from a permit under IMC Section 106.2?
4. An inspector finds a self-contained refrigeration system with 12 pounds of refrigerant and a 2 horsepower motor installed with no permit. Is a permit required?
5. A furnace serving an occupied clinic in a commercial building fails and must be replaced immediately. Under the IMC, when is the permit application due?
6. A permit application for a boiler installation was filed and then sat with no action by the owner. After how many days is it deemed abandoned unless pursued in good faith?
7. A mechanical permit was issued on January 10 and no work was started. A contractor arrives on the 200th day to begin. What is the status of the permit?
8. A contractor asks to close a ceiling grid over new duct runs because the inspector is running late for the rough-in inspection. What does the IMC say?
9. Under IMC Section 108.2, who is responsible for scheduling the required mechanical inspections?
10. When is the underground inspection made for buried mechanical piping under IMC Section 108.2?
11. A hydronic system at a rehab project is ready for its pressure test. Who performs the test and who witnesses it under IMC Section 108.3?
12. A gas utility technician is asked to turn on service to the gas line for a new rooftop unit before the final inspection. What does IMC Section 112 require?
13. A community center owner plans to change a former retail space into a child care room, which brings new special mechanical provisions. What does IMC Section 102.5 require?
14. A tenant adds two new rooftop units to an existing building system. Does the entire existing system have to be brought up to the current code?