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Nampa, ID Accessory Structures: ADU Rules (2026)

Some Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Nampa, ID, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Max size: 500 square feet of livable space
Bedroom limit: One bedroom only
Lot requirement: Same lot as single-family home
Utilities/address: No separate utilities or address
Zoning status: Permitted by right in most residential zones

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Idaho under recent ADU streamlining laws. The Nampa, ID rules below cover local size, height, and setback requirements.

Summary

Nampa allows one detached accessory dwelling per single-family lot, capped at 500 square feet with only one bedroom, no separate address, and no separate utility connections.

A detached accessory residential dwelling unit as a separate structure, is only allowed on the same lot/parcel as a single-family detached dwelling, provided they contain only one bedroom, no separate address, no separate utilities for their use. They may be combined with or be part of another detached structure such as a detached garage. The square footage of the accessory residential use within the detached structure, may not exceed 500 square feet of livable space.

View official code

Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 16 Update 1).

Full Breakdown

Nampa treats a detached accessory dwelling as a limited land-use category, not a general housekeeping structure: it must sit on the same lot as an existing single-family detached home, contain no more than one bedroom, carry no separate street address, and connect to no separate utility meters. The zoning ordinance caps the livable accessory space at 500 square feet and allows it to be built into or combined with another detached structure like a garage. The use is listed as permitted-by-right on residential lots under the citywide zoning use table, so no conditional use permit is required if the standards are met.

Violations & Fines

Building an ADU over 500 square feet, adding a second bedroom, or placing one on a lot without a single-family home is a zoning violation, punishable as a misdemeanor with each day a separate offense under city code.

Frequently Asked Questions

Can I build a detached ADU on any lot in Nampa?

No. Nampa's zoning code allows a detached accessory dwelling only on a lot that already has a single-family detached home, never on a lot with multiple dwelling units.

How big can a Nampa accessory dwelling be?

Up to 500 square feet of livable space with a single bedroom; it can stand alone or be combined with another accessory structure like a detached garage.

Does a Nampa ADU need its own utility hookup?

No: the code bars a separate address and separate utility connections for a detached accessory dwelling; it must share the primary home's service.

Sources & Official References

Other rules in Nampa

Shed & Carport RulesSome Restrictions Fence Regulations: Fence Permit RequirementsSome Restrictions Public Conduct: Skateboarding RulesSignificant Restrictions Public Conduct: Public UrinationSome Restrictions Public Conduct: Loitering RulesSome Restrictions Public Conduct: Aggressive PanhandlingSignificant Restrictions Business Licensing & Operations: Tattoo & Body ModificationSome Restrictions

All Nampa rules

How Nampa compares: Easiest Cities to Build an ADU·Compare Nampa to another location·View the Idaho accessory structures overview

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