Published
The Airport Overlay around Stanford Field: thirty feet, and the barn that needs a permit
An overlay that regulates height, and trees
St. Anthony has an airport, and the county has a zoning district built around it. Almost nobody buying or building on the valley floor knows the Airport Overlay Zoning District exists, and it is one of the few rules here that can restrict what you put up on ground that looks entirely ordinary.
The code names the two facilities it protects: Stanford Field and the Henrys Lake Airfield. Around each, the overlay consists of all land lying beneath the approach, transitional, horizontal and conical surfaces — shapes projected outward and upward from the runway, shown on supplements to the official zoning map.
Its stated purpose is to provide for the safety of pilots and passengers and to protect a substantial investment of public funds by keeping land use around the airports compatible with their continued safe use.
The four zones, and how far they reach
| Zone | How the code defines its extent |
|---|---|
| Utility runway visual approach zone | Inner edge coincides with the primary surface and is 250 feet wide, expanding uniformly to 1,250 feet at a horizontal distance of 5,000 feet, centred on the extended runway centreline |
| Transitional zones | The areas beneath the transitional surfaces, running out from the sides of the primary and approach surfaces |
| Horizontal zone | Established by swinging arcs of 5,000 feet from the centre of each end of the primary surface of each runway, and joining the arcs with tangent lines |
| Conical zone | Commences at the edge of the horizontal zone and extends outward a further 4,000 feet |
Add those up and the outer edge of the conical zone sits a considerable distance from the runway — the horizontal zone alone is built on arcs of nearly a mile, and the conical zone adds most of another mile beyond it. That is a lot of valley-floor ground, and most of it does not feel like airport land at all.
One rule prevents confusion where the shapes overlap: an area in more than one zone is treated as being only in the zone with the more restrictive height limitation.
What the height limits actually are
The limits are mostly expressed as slopes rather than as fixed heights, which is what makes them hard to reason about from a map alone.
- Utility runway visual approach zone: slopes twenty feet outward for each foot upward, beginning at the end of and level with the primary surface, extending 5,000 feet along the extended runway centreline.
- Transitional zones: slope seven feet outward for each foot upward from the sides of the primary and approach surfaces, up to 150 feet above the airport elevation, and further transitional surfaces run at the same seven-to-one slope out to where they meet the conical surface.
- Horizontal zone: a flat ceiling of 150 feet above the airport elevation.
- Conical zone: slopes twenty feet outward for each foot upward from the edge of the horizontal zone at 150 feet, extending up to 350 feet above the airport elevation.
The seven-to-one transitional slope is the aggressive one. Close in to the sides of the runway, the permitted height rises only one foot for every seven feet you move away, so ground near the flanks of the approach is where the limits actually bite on a normal building.
The thirty-foot exception, and why it matters more than the slopes
For nearly every house, the relevant provision is not a slope at all. It is the exception.
“Nothing in this Ordinance shall prohibit the construction or maintenance of any structure of 30 feet or less in height, or the growth of any tree to a height up to 30 feet above the surface of the land within the horizontal and conical zones.”
— Fremont County Development Code, 2011 Edition (Ordinance 2011-04), section 6.03.050. Retrieved 19 August 2026
Within the horizontal and conical zones — which between them cover the great majority of the affected ground — anything up to thirty feet is fine. A single-storey or two-storey house is comfortably inside that. So is a shelter belt, until it grows.
Two things to notice. The exception covers the horizontal and conical zones; it is not offered in the same terms for the approach and transitional zones, where the slopes govern from much lower down. And it is subject to topography: the code repeatedly qualifies the equivalent permit exemptions with the words “except when, because of topographic features, such a tree or structure would extend above the height limits”. Ground that sits high relative to the airport does not get the full thirty feet.
The permit rule that catches farm buildings
This is the provision most likely to surprise someone on valley-floor acreage. Inside the overlay, the county expands what needs a permit beyond the ordinary requirement, to include two things:
- The planting of any tree with a growth habit of more than 30 feet. Not a tree that is thirty feet now — a tree that will get there.
- The construction of any building or structure more than 30 feet in height that would otherwise be exempt from needing a permit at all — and the code says in parentheses that this includes agricultural outbuildings and similar accessory structures.
So a tall agricultural building, which elsewhere on the valley floor goes up under the agricultural structure exemption without a building permit, needs a permit inside the airport overlay if it exceeds thirty feet. A grain leg, a tall equipment shed or a hay barn with clearance for a stacker can all pass that mark comfortably.
The relief runs the other way for modest things. No permit is required within the horizontal and conical zones for trees with a growth habit under thirty feet or for exempt structures under thirty feet, unless topography would push them above the limits. The same relief applies within the approach zones at a horizontal distance of not less than 4,200 feet from each runway end.
It is not only about height
The chapter carries use restrictions that have nothing to do with how tall anything is. No use in any of these zones may:
- Create electrical interference with navigational signals or radio communication between the airport and aircraft.
- Make it difficult for pilots to distinguish between airport lights and other lights.
- Result in glare in the eyes of pilots using the airport.
- Impair visibility in the vicinity of the airport.
- Create bird strike hazards.
- In any other way endanger or interfere with the operation of aircraft.
Two of those are worth pausing on for a valley-floor build. Exterior lighting is a design decision that people make late and cheaply, and a bright unshielded yard light on the approach line is precisely what the glare and light-confusion provisions describe. And the bird strike provision has teeth for anyone contemplating a pond, a feedlot or anything else that reliably concentrates birds near a runway.
What to check before you commit
- Is the parcel inside any of the four zones? The boundaries are on supplements to the official zoning map, held at the Planning and Building Department.
- If it is, which zone — and remember that overlapping zones default to the more restrictive limit.
- Does anything planned exceed thirty feet, including a barn, a shop or a silo that would otherwise be exempt?
- Is the ground high relative to the airport elevation, which erodes the thirty-foot allowance?
- Are you planting anything with a mature height above thirty feet, which needs a permit in its own right?
- Does the lighting plan create glare toward the approach, and has anyone looked at it from that direction rather than from the house?
- If the parcel is inside city limits rather than county ground, does the city's own permit path apply on top of the overlay, since the two are separate questions?
For most houses the answer is that the overlay changes nothing at all — thirty feet is a generous allowance for a home. It is the tall accessory building, the shelter belt and the yard light that turn it into a live question, and all three are cheap to plan around and expensive to fix.
Common questions
What is the Airport Overlay Zoning District?
A county zoning overlay covering all land beneath the approach, transitional, horizontal and conical surfaces around the airports serving Fremont County, which the code names as Stanford Field and the Henrys Lake Airfield. Its purpose is pilot and passenger safety and protecting public investment in the airports.
How far does the overlay reach?
Further than most people expect. The horizontal zone is built on arcs of 5,000 feet from the centre of each end of the primary surface, and the conical zone extends a further 4,000 feet beyond the edge of that. The approach zone runs 5,000 feet along the extended runway centreline.
Can I still build a normal house?
In the horizontal and conical zones, yes. The code states that nothing in the ordinance prohibits construction of any structure of 30 feet or less in height, or the growth of any tree to 30 feet, within those zones. A one or two storey house sits comfortably inside that.
Does the thirty-foot allowance always apply?
No. It is stated for the horizontal and conical zones, and the equivalent permit exemptions are qualified by topography: where topographic features would cause a tree or structure to extend above the height limits, the exemption does not hold. High ground relative to the airport erodes it.
Do agricultural buildings need a permit inside the overlay?
If they exceed 30 feet, yes. The code expands permit requirements inside the overlay to include construction of any building or structure more than 30 feet in height that is otherwise exempt from a permit, and states in parentheses that this includes agricultural outbuildings and similar accessory structures.
Is planting trees regulated?
Inside the overlay the permit requirement expands to include the planting of any tree with a growth habit of more than 30 feet. The test is the mature height the tree will reach, not the height at planting.
What happens where two zones overlap?
The code states that an area located in more than one of these zones is considered to be only in the zone with the more restrictive height limitation.
Are there rules that are not about height?
Yes. No use in any of these zones may create electrical interference with navigational signals or radio communication, make it difficult for pilots to distinguish airport lights from other lights, result in glare in pilots' eyes, impair visibility near the airport, create bird strike hazards, or otherwise endanger or interfere with aircraft.
Could a pond be a problem?
It is worth asking about. The use restrictions expressly include creating bird strike hazards, so anything that reliably concentrates birds near a runway falls within what the chapter is aimed at. That is a question for the county rather than an assumption either way.
Where do I find out whether my parcel is inside it?
The zones are shown on supplements to the Official Zoning Map of Fremont County, held by the Planning and Building Department. Since the boundaries are geometric projections rather than property lines, this is one to confirm rather than estimate from a map.