Published
What actually differs from lot to lot on the Ashton corridor?
Start with what does not vary
Two of the numbers people expect to negotiate are fixed countywide, and knowing that saves a lot of wasted conversation. Fremont County Ordinance 2005-02 sets the minimum frost depth for footings at 32 inches — and the ordinance says it in one flat sentence, with no district qualifier attached:
“Section 4. Minimum Frost Depth for Footings: The minimum frost depth for footings shall be 32 inches.”
— Fremont County Ordinance No. 2005-02, Section 4 (county-published PDF, retrieved 13 August 2026)
Compare that with Section 3 of the same ordinance, which does nothing but name districts and assign each a different number. One section applies everywhere; the other exists precisely because the corridor is not uniform. The county also builds to the 2018 IRC, 2018 IBC and 2018 IECC, which apply the same way on every lot here.
So when a seller, a neighbour, or a plan drawn elsewhere suggests your footings can be shallower because the lot is lower, that is not a lot-to-lot variable. It is the same rule everywhere in the county.
The variable that moves the most money
Ground snow load is set by district, and the districts do not follow the way people describe the area. Ordinance 2005-02, Section 3 puts the Ashton District at 90 PSF and the North Fork Highlands District at 115 PSF. That is a 25 PSF gap — roughly a 28% increase in design snow load — between two districts whose boundary runs through country that looks continuous from the highway.
A roof engineered for 90 and a roof engineered for 115 are different roofs: deeper members or tighter spacing, a load path sized to match, and more weight arriving at footings that already have to reach 32 inches. It is not a change you discover after the trusses are ordered.
And here is the part worth knowing before you start: the county's snow-load zone map is published as a scanned image rather than as searchable text or a queryable map layer. You cannot look up a parcel number and get an answer. You look at a picture, and then you call and confirm. That is a perfectly workable process — it is just not one you can do from a listing at midnight, and it is why the 115 PSF district catches people who assumed Ashton's figure applied to everything nearby.
| Question | Where the answer actually lives |
|---|---|
| Which snow-load district is this lot in? | The county's zone map, confirmed with the building department — image only, so confirm rather than assume |
| What ground snow load do I design to? | Ordinance 2005-02 §3, once the district is settled |
| How deep do footings go? | Ordinance 2005-02 §4 — 32 inches, countywide, no lot-to-lot variation |
| Which code edition applies? | 2018 IRC / IBC / IECC, corridor-wide |
| Can this lot take a conventional septic system? | Eastern Idaho Public Health, on a site evaluation — a separate file from the building permit |
| What will power cost to reach the building site? | The serving utility, quoted per lot by distance |
| Who maintains the access, summer and winter? | Whoever holds the road — and the arrangement does not automatically transfer with a sale, so it belongs in writing before closing |
| What do the covenants allow? | The subdivision's recorded CC&Rs, which bind independently of the county and are often more specific about size, height and materials |
The wastewater answer is per-lot, and it is a real gate
Septic is permitted through Eastern Idaho Public Health, not through the county building department — a separate file, on its own timeline. What it depends on is soil, depth to groundwater, and setbacks, all of which are genuinely lot-specific. Two neighbouring parcels can produce a routine conventional drainfield and an engineered alternative at several times the cost.
Because it is the step most capable of returning a bad answer, it belongs early in diligence rather than late — the order to do this in is worth following, since the site evaluation is the one that can turn a lot you already own into a lot you cannot build the house you wanted on.
| What the evaluation examines | Why it moves between neighbouring parcels |
|---|---|
| Soil profile and its ability to accept effluent | Soils change over short distances, especially near a river corridor where deposition has layered them unevenly |
| Depth to groundwater | Follows the water table rather than the property line, and rises seasonally — the answer in September is not the answer in May |
| Setbacks from wells, surface water and boundaries | Fixed distances applied to a specific parcel's shape; a narrow or awkward lot can run out of compliant space entirely |
| Usable area for the drainfield and its replacement | The system has to fit twice over, which quietly rules out the building footprint you had in mind on a small lot |
Distance is its own line item
Everything that has to reach a rural building site is priced by how far it has to come, and none of it shows up in a per-square-foot number. Four to price per-lot rather than per-region:
- Power from the nearest service point. The serving utility quotes this by distance and will put it in writing; on a remote parcel it is a substantial figure and it is the one buyers most often never ask for
- The driveway. Length, the approach onto the public road, and whatever the ground under it needs — a long drive is a construction project, not an afterthought
- Haul. Every load of concrete, gravel, lumber and fill is priced partly by how far it travelled, and the distance applies to every load rather than once
- Mobilisation. Getting machines to the lot and home again costs about the same for a small job as a large one, which is why bundling work into one visit is worth planning for
Ask for written figures on the specific lot before you treat a remote parcel as cheap land — the cost page explains why these inputs, not the finishes, are what actually separate two bids.
The six questions to settle before you commission drawings
- Which snow-load district? Confirmed with the county, in writing, before an engineer starts
- What does the site evaluation say? The septic answer is per-lot and can be a no
- How far is power, and what has the utility quoted in writing?
- Who maintains the access, in summer and in winter, and does that arrangement transfer with the sale?
- What do the covenants say? They bind independently of the county, and they are often more specific about size, height and materials
- What is excluded from the builder's price? The exclusions list is where corridor-specific costs hide
None of these are exotic. All of them are cheaper to answer before a purchase than after, and every one of them is a question a corridor builder has answered many times — which is itself a reason to talk to one early. The permit walkthrough shows where each answer ends up in the county file.
Common questions
Does the snow load change from lot to lot around Ashton?
Not lot by lot, but district by district — and the districts do not follow how people describe the area. Fremont County Ordinance 2005-02, Section 3 sets the Ashton District at 90 PSF and the North Fork Highlands District at 115 PSF. That 25 PSF gap is roughly a 28% difference in design snow load, and it can fall between parcels only a few miles apart.
How do I find out which snow-load district my lot is in?
The county publishes a snow-load zone map, but it is a scanned image rather than searchable text or a queryable map layer — you cannot enter a parcel number and get an answer. Look at the map to orient yourself, then confirm the district with the Fremont County building department at (208) 624-7200 and get the answer in writing before an engineer starts work.
Does frost depth vary by elevation on the corridor?
No. Fremont County Ordinance 2005-02, Section 4 sets the minimum frost depth for footings at 32 inches countywide — not by district and not by elevation. If a plan drawn elsewhere, or a neighbour, suggests shallower footings because a lot sits lower, that is not a local variation you can use.
Which building codes apply on the Ashton corridor?
The 2018 IRC, 2018 IBC and 2018 IECC, applied the same way across the corridor. The code edition is not a lot-to-lot variable, which makes it one of the easier things to settle early — the energy code in particular is worth reading before the window and insulation package is priced.
Is septic approval really separate from the building permit?
Yes, and it catches people. Septic is permitted through Eastern Idaho Public Health, on its own file and its own timeline, while the building permit runs through Fremont County. They are different agencies with different requirements, and the county's building file expects the septic question to already be answered.
Can two neighbouring lots need different septic systems?
Easily. The site evaluation looks at soil, depth to groundwater and setbacks, all of which vary across short distances — especially near a river corridor. One parcel can take a routine conventional drainfield while the one beside it needs an engineered alternative costing several times as much. It is the diligence step most capable of returning an answer you do not want.
What should I ask the utility about power?
For a written figure to reach the actual building site on the actual lot, not a general rate. Distance from the nearest service point drives the number, and on a rural corridor parcel it can be a substantial line item that never appears in a per-square-foot estimate. Get it before you treat remote acreage as inexpensive land.
Do covenants matter more than county rules here?
They are often more specific. Covenants bind independently of anything the county requires and routinely govern size, height, materials and outbuildings — so a design that satisfies the ordinance can still be refused. Read them before commissioning drawings rather than after, when changes cost real money.
What is the single most expensive thing to get wrong on a corridor lot?
Designing to the wrong snow-load district. Everything structural routes through that number — roof members, spacing, the load path down to the footings — so discovering after drawings or a truss order that the lot sits in the 115 PSF district rather than the 90 PSF one is a redesign rather than an adjustment. Confirming it costs one phone call.