By Kjel Jones — independent custom-home researcher for Ashton and the Henry’s Fork corridor. Not a builder and not a general contractor. Licensed Idaho real estate agent, LPT Realty.

Published 2026-08-28

Seventy feet: the county's wildfire requirement, and the plan that goes with the plat

Seventy feet, and a plan filed with the plat

Wildfire preparation on the corridor is usually discussed as good practice: clear the brush, limb the trees, keep the woodpile away from the house. All sensible. What is less widely known is that Fremont County has a code requirement about it, with a number attached, and that it applies to new construction and not only to subdivisions.

It lives in Appendix S of the Development Code, headed Wildfire Sensitive Areas. The core figure is this: the defensible space area extends seventy feet in all directions around any residential dwelling, or to the property line, whichever is less.

What clearance the code actually specifies

Note what the “whichever is less” clause does on a small lot. If your property line sits forty feet from the house, the required defensible space is forty feet, not seventy. The code does not ask you to clear a neighbour's ground — but it also does not relieve the neighbour of the same obligation around their own dwelling.

The six-foot limbing rule is the one most often half-done. Removing limbs below six feet is what breaks the ladder — the vertical continuity that lets a grass fire climb into the crowns. The code defines ladder fuels in exactly those terms: fuels providing vertical continuity that allow fire to carry from the surface into the crowns with relative ease.

Which ground counts as wildfire sensitive

The definition is more precise than “it is in the trees”, and it has a percentage in it.

“At Risk Wildfire Sensitive Areas are areas that have been identified as moderate to high risk on their most recent wildfire risk analysis which may include any area one acre or larger in size that has highly flammable species such as cedar or pines, where 80% or more of all the dominant trees, at crown level, are made up of such conifer species.”

— Fremont County Development Code, 2011 Edition (Ordinance 2011-04), Appendix S, section 1.02.060. Retrieved 19 August 2026

So the test has three parts: an area of at least one acre, dominated at crown level by conifers to 80 percent or more, and a moderate-to-high rating on the most recent wildfire risk analysis. The definition then extends to stands of predominantly deciduous species where terrain, slope and aspect combine for a substantial wildfire threat — which on a corridor lot with a south-facing slope is a real possibility even without a pine stand.

There is one exclusion worth knowing: the appendix does not apply to timber stands or pine plantations managed for timber production, wildlife, hydrology or recreation.

The plan you file, and the notice you owe the buyer

For any new subdivision or new construction in a wildfire sensitive area, the code requires a Wildfire Sensitive Area Plan submitted with the preliminary plat. It is a drawing, with a stated scale of 100 feet to the inch, on sheets sized consistently with the plat, and it must detail three things:

1. The defensible space around any proposed building site.
2. Areas to be cleared of non-fire-resistive vegetation adjacent to proposed roads and driveways.
3. Areas to be cleared of non-fire-resistive vegetation adjacent to overhead power lines.

The second and third items are the ones people forget, because they are about access and infrastructure rather than about the house. A driveway through unbroken timber is both the route the fire service uses to reach you and a corridor fire can run along, and the same is true of a line of poles — which is worth thinking about alongside how power actually reaches a corridor lot in the first place.

There is also a continuing obligation that runs to buyers. The code requires each individual lot purchaser to be notified of the requirements of the appendix, and of the need to notify the Planning Department of amendments to the Wildfire Sensitive Area Plan if the location of any proposed structure or driveway changes for construction reasons. Moving a house pad or re-routing a drive is not just a site decision; it is a change to a filed plan.

Water for firefighting, and the three-mile rule

The appendix also deals with something no builder mentions in a quote: whether there is water to fight a fire with.

Where public water is available, the location of hydrants is approved in consultation with the Fire Code Official, who must consult the proper fire department authority first. Where public water is not available — which describes most corridor acreage — the code requires the applicant to provide for the installation of a dry hydrant at a satisfactory water source within three miles of the proposed subdivision, if an existing dry hydrant is not already available.

A dry hydrant is a pipe and fitting set into a pond, creek or cistern so an engine can draft from it. Three miles is a generous radius, and an existing one nearby discharges the obligation. But it is a line item that belongs in a subdivision budget, and on remote ground it is not always cheap to satisfy.

The vocabulary the code uses, and why it matters

Appendix S defines its own terms, and the definitions are worth having because they are what an application will be read against.

• Defensible space — the area between improved property and a potential wildfire where fuels have been removed or modified, to protect life and property, to reduce the chance of fire spreading from improved property into wildland fuels, and to give firefighters a safe working area.
• Fuels — all combustible material in the wildland-urban interface, which the code lists as trees, shrubs, plants, grass, rotting wood, leaves and structures. Your outbuildings are fuel by the code's own definition.
• Fuel load — the volume of fuel in a given area, generally expressed as tons per acre.
• Fuel modification — any manipulation or removal of fuels to reduce the likelihood of ignition or the resistance to fire control.
• Ladder fuels — fuels providing vertical continuity that let fire carry from the surface into the crowns with relative ease.
• Wildland-urban interface — the area where structures and other human development meet or intermingle with wildland fuels, which is a fair description of most of this corridor.

The inclusion of structures in the definition of fuels is the one that changes how a site is read. A woodshed, a detached garage or a neighbour's outbuilding is not merely a thing to protect; under the code it is part of what is burning.

What to establish before you buy or design

• Has the parcel been rated on a wildfire risk analysis, and what was the rating?
• Is there an acre or more where conifers make up 80 percent or more of dominant trees at crown level?
• If it is mostly deciduous, do terrain, slope and aspect still combine into a substantial threat?
• Where would seventy feet of defensible space fall, and does the property line cut it short on any side?
• If the ground is in a platted subdivision, does a Wildfire Sensitive Area Plan already exist, and does your intended house position match it?
• Is there a dry hydrant within three miles, or is providing one part of the development obligation, and has anybody priced it?
• Does the intended house position leave seventy feet of workable ground on the side a fire would most likely come from, given slope and prevailing wind?
• Is the clearing implied by all of this compatible with what you actually wanted the lot to look like — which is a design question, not just a compliance one, and one worth settling alongside the other things that vary lot to lot.

Common questions

How much defensible space does the county require?

The code states the defensible space area extends seventy feet in all directions around any residential dwelling, or to the property line, whichever is less. On a small lot the property line caps the requirement.

What clearance is required close to the house?

No vegetation or woody growth within five feet of any structure, though Firewise ornamental planting or cultivated ground cover such as green grass, ivy or succulents is allowed provided it does not readily transmit fire. Tree crowns within ten feet of a structure must be pruned back to keep ten feet of clearance.

Do I have to limb the trees?

Yes. The code requires trees to be pruned to remove limbs located less than six feet above the ground surface. That is the rule that breaks up ladder fuels, which the code defines as fuels providing vertical continuity that let fire carry from the surface into the crowns.

What makes an area wildfire sensitive?

Identification as moderate to high risk on the most recent wildfire risk analysis. That may include any area one acre or larger where 80 percent or more of dominant trees at crown level are highly flammable conifer species such as cedar or pine, and can extend to deciduous stands where terrain, slope and aspect combine for a substantial threat.

Does this apply to a single house or only to subdivisions?

Both. The appendix states that any new subdivision or new construction in areas defined as wildfire sensitive must comply with its requirements.

What is a Wildfire Sensitive Area Plan?

A map filed with the preliminary plat, drawn at a scale of 100 feet to the inch on sheets sized consistently with the plat, detailing the defensible space around any proposed building site and the areas to be cleared of non-fire-resistive vegetation adjacent to proposed roads and driveways and adjacent to overhead power lines.

What if I move the house or the driveway later?

The code requires each lot purchaser to be notified of the need to tell the Planning Department about amendments to the Wildfire Sensitive Area Plan where the location of a proposed structure or driveway changes due to construction requirements. It is a change to a filed plan, not just a site decision.

Is there a requirement about water for firefighting?

Yes. Where public water is not available, the applicant is required, in consultation with the Fire Code Official, to provide for installation of a dry hydrant at a satisfactory water source within three miles of the proposed subdivision, if an existing dry hydrant is not available.

Are managed timber stands covered?

No. The appendix states that none of its provisions apply to timber stands or pine plantations that are managed for timber production, wildlife, hydrology or recreation.