Most metal buildings require a permit, but the threshold varies by jurisdiction — commonly somewhere between 100 and 200 square feet, with plenty of counties setting it higher or lower. Size is only one of five factors. Foundation type, whether the structure is enclosed, how you'll use it, and your setbacks all affect the answer, and none of it is set nationally. The only authoritative answer comes from your local building department.
That said, you can predict the answer accurately before you call. Here's how.
The Five Factors That Decide It
1. Square footage. Nearly every jurisdiction has an exemption threshold for accessory structures. Under it, no permit. Over it, permit. The number varies widely — 100, 120, 200 square feet are all common. Some counties use 400.
2. Foundation type. A structure anchored to a permanent concrete foundation is almost always permitted, regardless of size. A building set on gravel or ground anchors is sometimes treated as temporary or as personal property, which can change the answer entirely.
3. Enclosure. Open-sided structures — carports, run-in sheds, loafing sheds — are exempt in more jurisdictions than enclosed ones of the same footprint. Add walls and you often cross into permit territory.
4. Intended use. Storage is the easiest case. Anything with plumbing, permanent electrical, occupancy, or commercial activity raises the bar substantially and may change your risk category. Living space triggers full residential code review.
5. Location on the lot. Setbacks from property lines, easements, floodplain, wetlands, and lot coverage limits can require approval even where the structure itself would be exempt.
Permit vs Zoning: Two Different Approvals
This trips up a lot of buyers. A building permit confirms the structure is engineered and built to code. Zoning approval confirms it's allowed where you want to put it. You can easily need one and not the other, and a zoning problem is worse — a permit denial delays you, a setback violation can require moving a finished building.
HOA approval is a third, separate thing. Your HOA can prohibit a structure your county would happily permit. It has nothing to do with the county and you have to handle it yourself, usually in writing, usually before ordering.
What Your County Will Typically Ask For
Requirements vary, but most jurisdictions want some combination of:
- A completed application with owner and contractor information
- A site plan showing the structure's location, dimensions, and distances to all property lines
- Stamped engineering — drawings sealed by a licensed engineer, rated for local wind and snow loads
- A foundation or anchoring plan matching the base you're building
- Proof of ownership or a deed, sometimes a plat
- Fees, usually scaled to project valuation
Pre-engineered metal buildings have an advantage here: a certified building ships with stamped engineering rated for your address, which covers a large part of that list. An uncertified building doesn't, and in most permitted jurisdictions it simply can't be approved. If you know you need a permit, order the certified building — retrofitting engineering after the fact is expensive and sometimes impossible.
Certified vs Non-Certified
| Certified | Non-Certified | |
|---|---|---|
| Stamped engineering | ✓ Included, rated to your address | ✗ None |
| Can be permitted | ✓ Yes | ✗ Generally no |
| Wind/snow rating | ✓ Documented | ✗ Undocumented |
| Cost | ✗ Higher | ✓ Lower |
| Appraised value | ✓ Counts as permanent improvement | ✗ Often doesn't |
If there's any chance you'll need a permit, or any chance you'll sell the property, certified is the safer purchase.
Common Scenarios
Detached garage on a concrete slab. Permit, essentially always. Slab plus enclosure plus size puts you over every common threshold.
Open carport, 20x20, on gravel. Frequently exempt, but this is the single most jurisdiction-dependent case there is. See do I need a permit for a carport?
Agricultural building on farmland. Many states offer broad agricultural exemptions — but they're usually tied to genuine agricultural use, and "I have land" doesn't qualify. Verify the definition your state uses.
Storage building under the threshold, on ground anchors. Usually the easiest case. Still confirm setbacks.
Anything with a bathroom, a wood stove, or permanent power. Permit, plus separate trade permits. No exceptions worth planning around.
How to Get a Straight Answer in One Phone Call
Call your county or city building department and give them these six things:
- Exact dimensions and total square footage
- Whether it's open, partially enclosed, or fully enclosed
- Foundation type — ground, gravel, or concrete
- Intended use, stated plainly
- Distance to your nearest property lines
- Your parcel or tax ID number
Then ask three questions: Do I need a permit? What do you require in the submittal? What are my setbacks for an accessory structure?
Write down the name of who you spoke with and the date. If you're told no permit is required, ask whether they'll confirm that in writing or by email. That record is worth a great deal if the question resurfaces at closing when you sell.
What Happens If You Skip It
Building without a required permit typically means a stop-work order, fines, retroactive permit fees at a penalty rate, and — in the worst outcome — an order to remove the structure. It also surfaces during a property sale, where an unpermitted structure can hold up closing or get excluded from the appraisal. Some insurance carriers will decline a claim on an unpermitted building.
Permits are usually cheaper and faster than buyers expect. The consequences of skipping one are not.