If you've ever moved, you may have noticed that the rules changed when you crossed the town line. A shed that needed nothing at your old house needs a zoning permit at the new one. A fence height that was fine there is too tall here. People find this maddening, and it's fair to wonder why there isn't one set of rules.
There's a reason, and understanding it makes permit research much less confusing. It's also the reason we built PermitLogic AI the way we did.
Layer one: model codes
Most U.S. building rules start from model codes. These are written by standards organizations and updated on a regular cycle. The one most homeowners run into is the International Residential Code, which covers one- and two-family homes, along with model codes for plumbing, mechanical, energy and electrical work.
A model code isn't law on its own. It becomes law only when a state or local government adopts it. And they don't all adopt the same edition at the same time.
Layer two: the state
Many states adopt a statewide building code based on a model code edition, sometimes with their own changes. Some states set a minimum that towns must enforce. Some leave more to local governments. A few have different rules for different kinds of places. States also often control licensing for trades like electricians and plumbers, and things like septic systems and wells may fall under state or county health agencies.
Layer three: the county
In some places the county runs building inspections for towns that don't have their own department. Counties may also handle things like stormwater, soil erosion and septic review. In other places the county plays almost no role in a homeowner's permit.
Layer four: the town
Towns, cities, boroughs and townships enforce the building code, and many adopt local amendments to it. Then there's zoning, which is almost entirely local. Zoning decides where things can go on a lot, how tall they can be and how much of a lot can be covered. Fence heights, shed setbacks and pool locations are mostly zoning questions, which is why they vary so much.
On top of that, each office develops its own practices: what it wants in an application, whether it has handouts, how it schedules inspections.
Why you can't just look it up once
Put those layers together and you get real variation:
- Two neighboring towns may have adopted different code editions.
- One may have local amendments the other doesn't.
- Their zoning ordinances may define "front yard" differently.
- One may publish a deck handout; the other may publish nothing online.
- A rule you find in an article may come from a model code that your town amended, or from a town three states away.
That's why "Do I need a permit for X?" so often gets "It depends" for an answer.
How Sully handles the layers
We designed PermitLogic AI around this layered reality instead of pretending it doesn't exist. When you describe a project, Sully researches in a fixed order:
- Your town first. The official site, permit pages, fee schedules, code and zoning pages. Any links you paste, like your town's ordinance or a handout, are read before anything else.
- Then the county, for anything the town defers to it.
- Then the state, for adopted codes and statewide rules.
- Then the model code, as a last fallback, linked or paraphrased rather than pasted.
Every rule in your permit report is labeled with where it came from: Town, County, State or Model code. If a rule comes from a fallback layer, you can see that at a glance and know to confirm it with the town.
And when nothing is published
Some towns publish a lot. Some publish very little online. When Sully can't find a rule, the report says so plainly. It may show county or state rules, clearly labeled, and it tells you who to call and what to ask. Phone numbers, fees and quotes in the report are checked against the pages Sully actually read.
We think that honesty is a feature. A tool that always sounds certain is a tool that will sometimes be confidently wrong, and with permits, being wrong costs money and time. Every rule also has a "this looks wrong" button, because local knowledge sometimes beats what's posted online.
A note on "nationwide" answers
You'll find plenty of confident, nationwide-sounding answers online: a single height, a single size, a single rule for the whole country. They're usually describing a model code default, or one state's rule. They aren't wrong so much as incomplete. The useful habit is to ask of any rule you read: whose rule is this, and has my town adopted it, changed it, or added to it? That's the same question Sully asks of every rule it puts in your report, which is why each one carries a source label.
What this means for you
- Treat any rule you read online, including in our own blog, as a starting point.
- Look for your own town's sources first: its website, ordinances, handouts.
- When in doubt, call the office. Our post on 5 questions to ask your town makes that call quick.
- Keep notes of what you were told and by whom.
PermitLogic AI is designed to work for any U.S. town, using the same town, county, state, model code ladder everywhere. Results depend on what each town publishes, and your permit office always makes the final call.
Check with your local permit office
This post is general guidance, not your town's rule. Requirements, fees and timelines vary by town, and your local permit office makes the final call.
Written by Sully Studios, the team behind PermitLogic AI. How we research and write. Spotted an error? Email [email protected].