Published
What "custom" actually means here: plan sets, allowances, and the exclusions list
The county has already decided part of the answer
Whatever a builder means by custom, the permit file sets a floor. Fremont County will not approve a permit without a real engineered set:
“Two sets of detailed plans and supporting documents (Engineering Calculations) and truss designs are required before approval of permit… Plans must be submitted on a minimum of 11 X 17 paper.”
— Fremont County, Idaho, Pre-Construction Check List for Building Permits, revised 17 April 2026 (county-published PDF, downloaded and re-read 14 August 2026)
Add the county's other requirement — that structures within a 70 pound per square foot roof snow load be designed by an engineer or architect licensed in Idaho — and the corridor's design load settles it. On a corridor lot, a stamped engineered plan set is not an upgrade. It is the entry ticket. Any bid that assumes a catalogue plan can be adopted unchanged has not priced the job you are actually doing.
That is genuinely useful, because it means one part of “custom” is not negotiable and can be checked. Everything after it is.
The three things people mean by the word
| What is meant | What you are buying | Where the cost moves | How to spot it in a bid |
|---|---|---|---|
| Custom finishes | A builder's own plan, with your selections | Almost entirely in allowances | A long allowance schedule and no design fee line |
| Modified plan | An existing plan re-engineered for your lot and load | Engineering, plus whatever the changes cascade into | An engineering line item, and a named base plan |
| Fully custom | A design drawn for your lot from the start | Design fees up front, and a longer pre-construction phase | A separate design agreement before any build price exists |
None of the three is the right answer in general, and all three are legitimate. The problem is only that all three get described with the same word, and a bid comparison across two of them is not a comparison at all. Ask which one a quote assumes before you compare it to anything. The three categories above are the author's read of how the term gets used locally; every county requirement quoted on this page comes from the county's own published form.
Allowances: where a firm-looking number is not one
An allowance is a placeholder. The builder puts a sum in the contract for something you have not chosen yet, and the final bill moves to whatever you actually pick. Allowances are normal and necessary. They are also the most common reason a build finishes above its contract price, and the reason is arithmetic rather than bad faith — a low allowance makes a bid look competitive and costs the builder nothing.
- Ask what each allowance assumes, in product terms rather than dollar terms. “$12 a square foot for flooring” means nothing until you know what that buys in the showroom the builder actually uses.
- Check the big four first — cabinets, flooring, appliances and plumbing fixtures. They carry most of the movement on most jobs.
- Ask about lighting and trim. They are less often scrutinised and are where an ambitious spec quietly outruns a modest allowance.
- Ask what happens to an underrun. If you come in under an allowance, does the difference come back to you, and in what form?
- Ask when selections are due. A late selection on a long-lead item is a schedule problem before it is a money problem, and on a short building season a schedule problem is expensive.
- Compare allowance schedules side by side before comparing bottom lines. Two bids with the same total and different allowances are two different prices.
Exclusions: the list that decides the real number
Exclusions are the opposite of allowances — not a placeholder but an absence. Anything on the exclusions list is your cost, arriving later, usually at a worse moment. On corridor acreage the exclusions list matters more than it does in town, because more of the site work is genuinely unknown until someone digs.
- Well and septic. Frequently excluded, frequently the largest single unknown, and on a corridor lot the item most capable of changing whether the project happens at all.
- Power to the building. Priced by the serving utility from wherever its line currently ends, which means the number depends on a distance nobody has measured yet.
- Driveway and access. Length, grade and base material vary enormously between corridor lots, and a bid drawn without a site visit has guessed.
- Rock. Excavation priced as if the ground is diggable, with rock handled as an extra, is standard practice and worth naming out loud.
- Permit fees and the county's charges. The site plan review alone is $50.00, a deposit is due at submittal, and the whole file wants roughly four to six weeks — small money, but it belongs to someone in writing.
- Landscaping, fencing and final grade. Almost always excluded, almost always assumed included by the buyer, and on an acreage lot the gap between those two positions can be a serious number.
How to make two Ashton bids actually comparable
Ask both builders for the same three documents: the plan set they are pricing, the allowance schedule, and the exclusions list. Then read the second and third before the first. If a builder will not produce an allowance schedule and an exclusions list in writing, that is itself the answer, and it is worth more than a lower number.
The bid that looks high is often the one that has been honest about the site. On corridor acreage, where the well, the power run and the ground itself are all genuinely unknown until someone looks, the builder who has priced those realistically will always lose a naive comparison to the builder who excluded them. That is worth remembering when the spread between two numbers seems too large to explain.
What is actually published about corridor costs, and what drives the spread, is on the cost page. Which builders work this corridor and what each is known for is on the log, timber and SIP page. The diligence that has to happen before any of this is priceable is on the well and septic page, and the permit sequence it all feeds is on the permit path page.
Common questions
Does Fremont County require engineered plans for a custom home?
Effectively yes on the corridor. The county requires two sets of detailed plans with supporting engineering calculations and truss designs before a permit is approved, and separately requires structures within a 70 pound per square foot roof snow load to be designed by an engineer or architect licensed in Idaho.
Can I use a stock house plan on an Ashton lot?
You can start from one, but expect it to be re-engineered rather than adopted. The county needs a stamped set with engineering calculations and truss designs, so a catalogue plan becomes the starting point for an engineer's work. Budget the engineering as a line item rather than as a surprise.
What is an allowance in a building contract?
A placeholder sum for something you have not selected yet — flooring, cabinets, appliances, fixtures. The final bill moves to whatever you actually choose. Allowances are normal, but a low allowance makes a bid look competitive at no cost to the builder, which is why they are worth reading closely.
Which allowances move the most on a build?
Cabinets, flooring, appliances and plumbing fixtures carry most of the movement on most jobs, with lighting and trim close behind because they attract less scrutiny. Ask what each allowance buys in product terms at the supplier the builder actually uses, not just what the number is.
What is an exclusions list?
The list of things a bid does not include, which therefore become your cost later. On corridor acreage it commonly covers well and septic, the power run to the building, driveway and access, rock in the excavation, permit fees, and landscaping or final grade.
Why is one Ashton bid so much higher than another?
Often because it is more honest about the site. Where the well depth, the power distance and the ground conditions are genuinely unknown, a builder who prices them realistically loses a naive comparison to one who excludes them. Compare the exclusions lists before comparing the totals.
What should I ask a builder for before comparing quotes?
Three documents from each: the plan set being priced, the allowance schedule, and the exclusions list. Read the allowance schedule and exclusions list first. A builder who will not put those in writing has effectively answered a different question than the one you asked.
What does the county charge and how long does it take?
The site plan review is $50.00 and a deposit is due at submittal. The county asks applicants to allow approximately four to six weeks to review and approve plans, and warns that an incomplete application will not be accepted or processed at all.
Does "custom" mean the same thing to every corridor builder?
No, and that is the practical problem. It can mean your selections on the builder's own plan, an existing plan re-engineered for your lot, or a design drawn from scratch. All three are legitimate; comparing a bid for one against a bid for another is not a comparison.