Permit or Not

How this works

Short version: there is no national permit database, so anyone claiming a definite answer for every address in the country is guessing. This tells you the typical rule, what would change it, and who actually decides.

Why there is no simple answer

Permitting in the United States is run by roughly twenty thousand local authorities. Most adopt a version of the International Residential Code and then amend it — and the amendment is usually where people get caught. A shed exemption of 120 square feet in the model code turns up locally as 100, or 144, or 200.

We measured how much this matters. 41.2% of the US population lives in a state where the state code does not settle it — eleven home-rule states plus twelve mixed ones, about 138 million people whose answer is a county or city decision. And 30.1% of ZIP codes cross a county line, so for roughly a third of visitors the honest answer names two possible offices rather than one.

The two gauges

The permit needle is clamped. It can lean hard but it can never touch either end, because whether your specific project needs a permit depends on a jurisdiction we have probably not read. A dial that bottoms out at “not needed” is a picture somebody screenshots and builds from.

The consequence meter is not clamped. Whether an unvented gas appliance produces carbon monoxide does not vary by county. That is physics, and when something can genuinely hurt you the gauge is allowed to say so plainly.

Where the answers come from

• The baseline is the IRC’s own exemption list (R105.2), which most US jurisdictions adopt and then amend. It is published, citable and stable.
• Geography is US Census data: the 2020 county file, the 2020 ZCTA-to-county relationship file, and the 2024 population estimates.
• State code adoption — which edition each state works from, and whether that binds statewide — is recorded per state with the source and the date it was read.
• Local rules are recorded only where someone has actually read them. Our database physically cannot store a rule without a source and a date attached, so a jurisdiction nobody has checked shows as unchecked rather than carrying a guess.

What people actually do

Some pages show the share of visitors who said they were going ahead without a permit. That is self-reported by people who came here looking the question up — a group already more likely than average to be weighing it. It is not a measure of what people generally do, and we do not put a percentage on it until at least forty people have answered.

What this is not

Not a permit decision, and not legal or engineering advice. We do not prepare, file or pull permits. The only answer that binds anyone is the one from the authority that would issue it.