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ADUs · Eagle, Idaho

ADUs in Eagle, built as real homes.

An ADU in Eagle starts with the lot. Lot size decides whether an ADU is allowed and how large it can be, and many Eagle neighborhoods add HOA and design review on top of city rules. Fortis is a Boise builder and developer working throughout the Treasure Valley. We sort out what your property allows before anyone pays for design.

Have a property in mind?

Call (208) 631-6067fortisbuildingco@gmail.com
Walnut cabinetry and a green glazed tile backsplash in the renovated 25th Street Residence kitchen in Boise, with the island and stainless hood to the right.
25th Street ResidenceRenovated home, kitchen · Photograph

What Eagle’s code allows today

Under Eagle’s zoning code (8-3-5, Accessory Dwelling Units):

  • A zoning permit is required before a building permit.
  • One ADU is allowed per parcel.
  • The minimum lot size for an ADU is 17,000 sq ft, unless approved through a development agreement or PUD.
  • Maximum ADU size depends on lot size:
    • 5,000 to 7,499 sq ft lot: 500 sq ft
    • 7,500 to 16,999 sq ft lot: 640 sq ft
    • 17,000 to 39,999 sq ft lot: 800 sq ft
    • 40,000 sq ft or larger: 1,200 sq ft
  • The ADU must meet the city’s off-street parking requirements.
  • The ADU can’t be sold separately from the main house, and the main house must exist or be built at the same time.

Avimor has its own development code, and ADUs there also need Avimor Design Review Committee approval.

The rules are changing

Idaho passed a new ADU law that took effect July 1, 2026. It limits how larger cities can restrict ADUs, including size caps, parking requirements, and owner-occupancy requirements, and gives cities until February 1, 2027 to update their codes. Eagle’s rules may change as a result. We confirm the current rules for your specific lot before design starts.

HOAs and design review

Many Eagle subdivisions have CC&Rs and architectural review. The new state law also changes what HOAs can do about ADUs, but how it applies depends on your covenants and when they were recorded. We review them early so there are no surprises after drawings are done.

How we work

  1. 01Understand the property: lot size, zoning, HOA, utilities, access.
  2. 02Define the ADU: what it’s for, where it sits, what it needs to cost.
  3. 03Design and budget together, so what’s drawn can be built.
  4. 04Build deliberately, with clear scopes and active project management.
Counter-height view across the renovated 25th Street Residence kitchen in Boise: the white quartz island with four black stools, walnut lower cabinets, and white oak flooring.
25th Street ResidenceRenovated home, kitchen · Photograph
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Common questions

Can I build an ADU on my Eagle lot?
It depends mainly on lot size and any development agreement, PUD, or HOA rules. Under current city code, lots under 17,000 sq ft generally need a development agreement or PUD approval. Send us your address and we’ll check.
How big can it be?
Under current code, 500 to 1,200 sq ft depending on lot size. That may change as Eagle updates its code under the new state law.
Can I rent it out?
The Eagle ADU section doesn’t address owner occupancy, and the new state law bars larger cities from requiring it. Confirm with us for your lot.
Can I sell the ADU separately?
No. It stays with the main house.