The honest range for 2026
In Bonneville County — Idaho Falls, Ammon, Iona, Ucon — a real custom home build runs $160 to $200 per finished square foot, with most projects landing around $175. That’s all-in: structural shell, mechanicals, interior selections at mid-to-high tier, soft costs, builder fee. It is not a lot, not a basement finish, and not finish upgrades above the mid tier.
[PLACEHOLDER — Curtis to confirm the 2026 range with current job actuals.]
What’s actually inside that per-square-foot number
The per-square-foot framing is the wrong way to think about a real budget. Here’s the breakdown from a typical 4,800 sq ft Guardian custom in Ammon:
| Phase | Share of total | Notes |
|---|---|---|
| Site work + foundation | 9–13% | Wildly variable based on lot. Soils report determines the spread. |
| Framing + sheathing | 14–17% | Truss design, snow load, height matter more than square footage. |
| Mechanicals (electrical, plumbing, HVAC) | 13–16% | Whole-home automation pushes the upper end. |
| Insulation, drywall, roofing | 9–12% | |
| Cabinetry + countertops | 8–11% | Largest variance from selections. |
| Flooring | 5–7% | |
| Trim, doors, windows | 7–9% | Window package alone can move 3% of total budget. |
| Finishes (paint, fixtures, hardware) | 5–7% | |
| Permits + soft costs | 2–4% | County-specific. |
| Builder fee + overhead | 8–12% | Cost-plus builds vs. fixed-price will look different here. |
[PLACEHOLDER — Curtis to validate percentages with a current job.]
The line items that surprise people
- Site work. A flat infill lot might run $25k. A view lot in the foothills with a soft-soil report and a deep utility run can hit $90k+ before a foundation is poured.
- Permits. Bonneville County permit + impact fees on a 4,500 sq ft home in 2026 run roughly $X,XXX. [PLACEHOLDER number — confirm with current permit invoice.]
- Windows. A modest window package across a 5,000 sq ft home: $25–40k. A real architectural window package (oversized glass, multi-slide, premium frames): $80–120k.
- HVAC sizing. Eastern Idaho needs real cooling now, not just heat. Heat pump systems that handle both have moved the HVAC line item up 15–20% in the last three years.
Where Bonneville County differs from Madison or Bingham
- Permit timelines tend to be faster in Bonneville than Madison. Plan-review queues in Rexburg can push you out 6–8 weeks at the wrong time of year.
- Sub availability is best in Bonneville — most of the trade base is centered around Idaho Falls.
- Lot costs in Ammon and Iona have leveled out; lot costs in north Idaho Falls and east-of-the-river views are still climbing.
[PLACEHOLDER — Curtis to add 2-3 sentences of current Bonneville-vs-Madison color.]
What the per-square-foot number doesn’t include
- The lot
- Site retaining walls or hardscape
- Pool, hot tub, outdoor kitchen
- Landscape and irrigation past basic final-grade
- Detached garage or shop
- Furniture, window coverings, AV beyond basic wiring
If you’re trying to model a real budget, model these separately and add them on top — they’re the items that quietly turn a “$1.1M build” into a $1.35M out-the-door number.
How to get a real number — not a guess
The per-square-foot approach is useful for ballparking, but it can be 20% wrong in either direction on a specific plan and lot. The right answer is to put the actual plan and lot in front of a builder and let them run real numbers.
We’re building a tool that does exactly that — point it at your plan and your lot, and it returns a real Eastern Idaho cost number using live sub and supplier pricing. It launches later this year. The first batch gets early access.