Snow load · the flagship question
Ashton’s snow load is 90 PSF. The state’s own study says 103.
Published · every figure below was checked against its primary source on the date shown.
The county says 90. The state’s own study says 103.
Both numbers are real, both are current, and they do not mean the same thing. Fremont County adopted its ground snow loads in Ordinance No. 2005-02, which divides the county into districts and gives each one a single figure:
“Section 3. Ground Snow Load: The ground snow load shall be … 115 PSF. for the North Fork Highlands district. 90 PSF. for the Ashton District…”
“Section 4. Minimum Frost Depth for Footings: The minimum frost depth for footings shall be 32 inches.”
— Fremont County Ordinance No. 2005-02, Sections 3 and 4 (county-published PDF, retrieved 13 August 2026)
That 90 PSF is a code minimum applied to a whole district. The other number comes from Ground Snow Loads for Idaho — 2015, the University of Idaho study that Idaho structural engineers commonly design against, which models towns individually rather than in blocks.
Where the two disagree across the Ashton District
| Town | Elevation | U of I 2015 recommendation | County district value | Gap |
|---|---|---|---|---|
| Ashton | 5,260 ft | 103 psf | 90 PSF | +13 |
| Warm River | 5,297 ft | 108 psf | 90 PSF | +18 |
| Drummond | 5,607 ft | 114 psf | 90 PSF | +24 |
The study is explicit about where the Ashton figure comes from. Its footnote on the town reads:
“Ashton station (NWS) has a 50-yr ground snow load of 106 psf and elevation of 5,212 ft.”
— Al Hatailah & Godfrey, Ground Snow Loads for Idaho — 2015, University of Idaho, footnote 48
Why this matters more at Drummond than in town
The district is one value; the ground under it climbs almost 350 feet. A single figure stretched across that range will be conservative at the low end and thin at the high end, and Drummond sits at the high end. A house designed to exactly 90 PSF outside Drummond meets the county minimum and still sits 24 psf below what the state’s own reference recommends for its elevation.
- A minimum is not a recommendation. Meeting 90 PSF makes a design legal in the Ashton District; it does not make it the design the state’s reference points to.
- Elevation moves inside the district. The three corridor towns above span roughly 350 feet of elevation and share one district figure between them.
- Exceeding a minimum is normal engineering, not an upgrade — an engineer may design above the code floor wherever the site warrants it.
- The decision is nearly free at design stage and expensive afterwards, because it reaches into truss depth, spacing and bearing members.
- Bids diverge silently on this. Two builders pricing different snow loads are pricing different houses, and nothing on the face of the bid says so.
What to do about it, in order
- Confirm your district against the county’s Snow Load Zone Map and the building department at (208) 624-7200 — not against a neighbour’s memory.
- Ask your engineer, in writing, which ground snow load the design uses and why. One sentence, before plans are drawn.
- Ask what designing to the higher figure would add in framing cost. On many roofs the answer is smaller than people expect.
- Get the answer into the bid set so every builder is pricing the same roof. Two bids designed to different snow loads are not comparable.
The honest limits of this page
This is research, not engineering. The county figure is the enforceable minimum and the study is a recommendation; deciding what your particular roof is designed to is the job of a licensed Idaho structural engineer who has seen your plans, your site and your elevation. What this page is for is making sure the question gets asked while it is still free to answer.
Related reading on this site
- The 115 PSF district almost nobody names — the fourth district in the same ordinance, above Ashton
- The 32-inch frost depth — the other number from the same ordinance, and what it costs
- The county permit path — where snow-load certification enters the file
- The builder table — who builds here, and who runs engineered roof systems
Common questions
What is the ground snow load for Ashton, Idaho?
Fremont County Ordinance No. 2005-02 places Ashton in a district with a 90 PSF ground snow load. That is the figure the county building department applies to a permit file for a house in and around town.
Why does the University of Idaho study give a different number?
Because it is measuring a town, not a district. The county draws broad zones and assigns one value to each; the 2015 statewide study models each town's own elevation and snow record, and returns 103 psf for Ashton at 5,260 feet — 13 psf above the district figure.
Which number will my engineer design to?
That is the question to ask before plans are drawn, and the honest answer is that it depends on the engineer. The county figure is the code minimum; the state study is the reference many Idaho structural engineers design against. They are not in conflict — a design can exceed the minimum, and here it often should.
Is the county's 90 PSF wrong?
No — it is a minimum, and minimums are drawn coarsely on purpose. The point is that a minimum is a floor rather than a recommendation, and across the Ashton District the floor sits below what the state's own reference suggests for several towns in it.
What about Drummond and Warm River?
They sit in the same county district at 90 PSF, but the 2015 study recommends 114 psf for Drummond at 5,607 feet and 108 psf for Warm River at 5,297 feet. Drummond carries the widest gap in the corridor — 24 psf above the district figure.
What does a higher design load actually cost me?
It shows up in the roof structure: deeper or more closely spaced trusses, heavier ridge and bearing members, and sometimes a different roof pitch. It is a framing and engineering cost, decided at the design stage — which is exactly why it is cheap to ask about now and expensive to revisit later.
Where can I read the ordinance myself?
Fremont County publishes it in its online DocumentCenter. Be warned that it is a scanned fax image rather than a typed document, so it does not always search well; the passages quoted on this page are transcribed from that scan.
How do I know which district my lot is in?
The county publishes a Snow Load Zone Map, linked from the home page of this site. It is image-only with no searchable text, so read it against your legal description and confirm the district with the building department at (208) 624-7200 before designing anything.