Pick your project, answer two or three questions, and get the answer with the actual code sectionbehind it — not a forum guess. The logic below is the International Residential Code's own exemption list (Section R105.2, identical in the 2021 and 2024 editions), read and applied the way a plans examiner reads it. Written by an ICC-Certified Building Official.
PICK YOUR PROJECT
How the permit question actually works
People assume permits are a list of things that need one. The code is written the other way around: IRC R105.1 makes a permit the default for everything— construct, enlarge, alter, repair, move, demolish, or change the occupancy of a building, or install, alter, or replace any electrical, gas, mechanical, or plumbing system. Then R105.2 carves out a short, specific list of exemptions. If your project isn't on the list, it needs a permit. That's the whole game, and it's why the quiz above is short.
The numbers worth memorizing
200 sq ft — one-story detached accessory structures (sheds, playhouses) at or under this floor area are exempt. The IBC version is 120 sq ft, and many cities adopt that instead.
7 ft — fences at or under this height are exempt from a building permit (zoning is another matter).
4 ft — retaining walls at or under this height are exempt, measured from the bottom of the footing, and only with no surcharge behind them.
200 sq ft / 30 in — decks need all four: at or under 200 sq ft, no more than 30 inches above grade at any point, free-standing, and not serving the required exit door.
24 in — prefab pools shallower than this are exempt.
25 V / 50 W — low-voltage electrical work under both limits is exempt.
180 days — how long you have to start work before an issued permit expires (R105.5).
The three traps
Trap 1: exempt is not unregulated.The first sentence of R105.2 says the exemption doesn't authorize work that violates the code. Your permit-free fence still has to be a code-compliant fence, and if it isn't, the violation is enforceable with or without a permit on file.
Trap 2: the structure and the systems are separate questions.R105.1 lists building work and each trade system independently. The 10×10 shed is exempt; the circuit you run to it is not. The bathroom's new tile is exempt; moving the drain two feet is not.
Trap 3: the model code is not your local code. The IRC is what jurisdictions start from, not what they all end up with. Shed thresholds get amended down, fence rules get folded into zoning, and some departments keep their own exemption handouts. The quiz gives you the model-code answer and the section to cite — verify the local version with one phone call before you dig.
Why inspectors actually care
The exemption list isn't arbitrary. Read it again and a pattern shows up: everything on it is work you can see, reach, and fix after the fact — paint, countertops, a low deck, a short fence, a kiddie pool. Everything off it is work that gets buried— wiring behind drywall, pipe under a slab, footings under a tall wall, the ledger bolts holding a deck to the house. Inspections exist for the parts of a house nobody can check later. That's also why the “concealed pipe” rule in R105.2 is so blunt: replace hidden defective pipe and the code says it “shall be considered as new work.”
Common questions
If the quiz says exempt, can I just build it?
Not quite — three more gates. First, the exemption text itself says exempt work still has to comply with the code: R105.2 opens with "exemption from permit requirements of this code shall not be deemed to grant authorization for any work to be done in any manner in violation of the provisions of this code." Second, zoning is separate: setbacks, lot coverage, height limits, and easements apply whether or not a building permit does. Third, HOA covenants, floodplain rules, and historic districts are their own review. Exempt means no building-permit application — not no rules.
Why does my city say 120 sq ft for sheds when the IRC says 200?
Two codes, two numbers. The International Residential Code exempts one-story detached accessory structures up to 200 sq ft (R105.2). The International Building Code — which covers everything the IRC does not — sets its version of the same exemption at 120 sq ft (IBC 105.2). Many jurisdictions adopt 120 across the board or amend in their own threshold, which is why the handout at your permit counter may not match the model code. The local amendment always wins.
Do I need separate permits for electrical and plumbing even when the building is exempt?
Yes. IRC R105.1 lists building work and each trade system separately — a permit is required to install, alter, or replace any electrical, gas, mechanical, or plumbing system. A 120 sq ft shed can be exempt as a structure while the circuit you run to it still needs an electrical permit. This is one of the most common ways well-meaning DIYers end up with a red tag.
What actually happens if I skip a permit?
The usual sequence: a stop-work order when it is noticed (neighbors and online listings are how it gets noticed), a permit fee that most local fee schedules multiply as an investigation or after-the-fact fee, and — the expensive part — opening up finished work so it can be inspected. Unpermitted work also surfaces at the worst times: home sale disclosures, appraisals, and insurance claims after a fire or water loss. The permit is almost always the cheap option.
My water heater died on a Saturday. Do I really have to wait for a permit?
No — the code has an emergency rule. IRC R105.2.1 lets equipment replacements and repairs proceed immediately in an emergency, as long as the permit application is submitted "within the next working business day" to the building official. Swap it Saturday, file Monday.
How long is a permit good for once I have it?
Under IRC R105.5, a permit becomes invalid if the work does not commence within 180 days of issuance, or if more than 180 days pass between inspections once started. The building official can grant extensions in writing — 180 days at a time — if you ask in writing and show justifiable cause.