What generally drives the answer
Use
This is the biggest factor. Many jurisdictions treat genuine agricultural buildings differently from everything else, sometimes exempting them from permitting or from parts of the building code. A shop, a garage, anything with living space, or anything the public enters is normally treated as a regular structure with full requirements.
Size
Many places have a square-footage threshold below which a detached accessory structure doesn't need a permit. The number varies a lot between jurisdictions, so a threshold you read about somewhere else means nothing for your parcel.
Location
Setbacks from property lines, easements, floodplain, wetlands, and how close you are to a road or utility all matter, and these are often enforced separately from the building permit itself.
Whether you're on well and septic
Anything with plumbing usually brings the health department into it, which is a separate approval from the building permit.
Zoning versus building
Two different approvals, often two different offices. Zoning decides whether you're allowed to put that use there. The building permit decides whether the structure is built correctly. Getting one doesn't get you the other.
The agricultural exemption, and its limits
Where agricultural exemptions exist, they typically hinge on genuine agricultural use of the property and the building. They're also narrower than people assume.
What frequently falls outside them: a shop for a business, a building with an office or living quarters, storage for non-agricultural equipment, or anything on a parcel that isn't actually farmed. And exemptions commonly don't cover electrical or plumbing, which need their own permits regardless.
Worth knowing: using an exemption you don't qualify for can surface years later — when you sell, refinance, insure, or when a neighbor complains. Retroactive permitting on a finished building is far more expensive than permitting it up front.
Permit versus engineering stamp
These get conflated and they're different things.
A permit is your jurisdiction's approval to build.
An engineering stamp is a licensed engineer sealing the structural design and taking professional responsibility for it.
Some jurisdictions require a stamp for any permitted structure, some only above a size threshold, some only for certain uses. Many post frame suppliers provide stamped engineering for their own building packages, so ask your supplier before you hire an engineer separately. What goes into a permit-ready plan set.
The call to make, and what to ask
Call the building department for the county or municipality where the parcel sits. Have your parcel number ready. Ask:
- Does a building of this size and use need a permit here?
- Is there an agricultural exemption, and would this building qualify?
- What drawings do you require in the submittal?
- Do you require stamped engineering?
- What ground snow load and wind speed should the building be designed for?
- What are the setbacks for this parcel?
- Do I need separate zoning approval?
- Do electrical and plumbing need separate permits?
- What's the current review turnaround?
Question five matters even if you end up not needing a permit — those numbers determine how the building has to be engineered, and your supplier needs them to quote correctly.
Timing
Start the permit conversation before you order materials, not after. Review turnaround varies from days to many weeks depending on the jurisdiction and time of year, and a building sitting on a trailer waiting for approval is a problem. It's also cheaper to change a design on paper than to change an order.
What your builder should be able to give you
A builder working from a real 3D model should be able to hand you a dimensioned plan set — plans, elevations, sections and framing layouts — generated from the building you actually agreed on, consistent across every view.
Redline 3D produces downloadable permit-ready plan sets from the same model that generates the material takeoff, across post frame, red iron and stick frame. Whether your jurisdiction also wants a stamp is between you and your building department.
This is general information, not legal or code advice. Your building department is the authority on your parcel.