Boise ZOA25-000013 ADU Ordinance Amendment Walkthrough

Scope & Disclaimer

This brief summarizes changes enacted by City of Boise Zoning Ordinance Amendment ZOA25-000013, effective February 15, 2026. It is NOT legal advice. Zoning regulations are subject to change, and individual parcels may carry additional restrictions (historic overlays, HOA covenants, utility constraints). Verify current standards at the City of Boise Zoning Code before any development decision. For comprehensive ADU regulations, see the Boise ADU Guide.

What Changed

On February 15, 2026, the City of Boise enacted ZOA25-000013, amending Boise Code §11-02-01 to expand accessory dwelling unit (ADU) development rights across all residential zoning districts. Two changes drive the amendment's impact:

1. Owner-occupancy requirement eliminated. Prior to February 2026, at least one unit on the lot (primary dwelling or ADU) had to be owner-occupied. Under the new ordinance, neither unit requires owner occupancy. Investment buyers can now acquire a property, build an ADU, and rent both units without living on-site.

2. Per-lot ADU cap increased from one to two. Lots meeting minimum size and setback requirements can now support up to two detached ADUs in addition to the primary dwelling, for a maximum of three dwelling units per lot in most residential zones.

The amendment applies citywide to all residential zoning districts (R-1A, R-1B, R-1C, R-2, R-3, R-4, R-OD). Lot size minimums, setback requirements, and design standards remain unchanged from the prior ordinance. The City continues to offer eight pre-approved ADU plan sets at no cost to streamline permitting.

Verify current standards at the City of Boise Zoning Code before any development decision.

Why It Matters for Investors

Renew take: The elimination of the owner-occupancy requirement transforms ADU economics from a homeowner amenity play into a pure rental-income strategy. Prior to February 2026, only owner-occupants could legally build and rent an ADU. Investment buyers had to either live on-site or forgo the ADU income stream. That constraint is gone. A buyer can now acquire a single-family lot, add one or two ADUs, and operate all units as rentals without ever occupying the property.

The two-ADU cap amplifies the impact. On a standard 6,000-square-foot R-1C lot, an investor can now deliver three rental units: the primary dwelling plus two detached ADUs. Assuming conservative rents of $2,200/month for the primary and $1,400/month per ADU, gross annual rental income reaches $61,200 on a single lot. [DATA AGE: 10 months old — verify current Q1 2026 rental rates] Compare that to the $26,400 annual income from the same lot with only the primary dwelling rented. The ADU amendment effectively triples the income potential of infill land.

Impact by Asset Class

Land

The amendment increases the residual land value for infill lots in neighborhoods where ADU construction is feasible. Buyers underwriting land acquisitions can now model two additional income streams per lot, raising the maximum supportable land price. Expect upward pressure on lot pricing in The Bench, SE Boise, and West Boise, where lot sizes commonly exceed the 5,000-square-foot minimum and zoning permits detached ADUs.

Renew take: Land sellers who haven't updated their pricing assumptions since February 2026 are leaving money on the table. A 6,000-square-foot R-1C lot that penciled at $120,000 under the one-ADU rule now supports a $180,000–$200,000 acquisition price when underwritten with two ADUs. Buyers with updated models will outbid legacy comps.

SFH Rentals

Existing single-family rental portfolios gain immediate value-add potential. An investor holding a rental property on a conforming lot can now add one or two ADUs without selling the property or moving in. The amendment converts static rental assets into development opportunities. Expect increased acquisition activity from operators targeting older SFH rentals on oversized lots across Boise residential zones.

Infill Development

Infill builders and small-scale developers gain a new product type. A builder acquiring a teardown lot can now deliver a new primary dwelling plus two ADUs as a turnkey rental package or sell the improved property to an investor at a higher exit multiple. The three-unit configuration offers an alternative to small multifamily projects with different construction cost and regulatory profiles.

Constraints and Risks

• Lot size minimums. Most residential zones require a minimum 5,000-square-foot lot to support even one detached ADU. Smaller lots remain ineligible.
• Setback and height limits. ADUs must meet the same setback and height standards as accessory structures in the underlying zone. Tight lots may lack the buildable area for two ADUs even if the lot size qualifies.
• Historic overlays. Properties within the North End Historic District or other designated overlays face additional design review and may be prohibited from adding ADUs. Verify overlay status before acquisition.
• HOA restrictions. Private covenants may prohibit ADUs regardless of zoning. Title review is non-negotiable.
• Utility capacity. Older neighborhoods may lack the sewer, water, or electrical capacity to support three units per lot. Confirm utility availability with the City before closing.

Renew take: The two-ADU cap is a ceiling, not a guarantee. Most Boise lots will support zero or one ADU due to size, setback, or overlay constraints. Buyers must underwrite each parcel individually. Do not assume every residential lot qualifies for the maximum configuration.

Adoption Timeline

The City of Boise began drafting the ADU amendment in mid-2025 in response to state-level housing legislation (Idaho SB 1352 and SB 1354) that required municipalities to permit ADUs in all residential zones. The City Council approved ZOA25-000013 on February 1, 2026, with an effective date of February 15, 2026. The ordinance is now in force citywide.

As of March 2026, the City reports 1,962 ADU units approved since the original ADU ordinance took effect in 2024. The February 2026 amendment is expected to accelerate ADU permitting activity, though the City has not yet published post-amendment approval data.

Next Steps for Operators

1. Audit existing portfolio. Identify rental properties on lots exceeding 5,000 square feet in non-overlay zones. Model the economics of adding one or two ADUs to each property.
2. Update land underwriting models. Revise residual land value calculations to reflect two-ADU income potential. Adjust acquisition pricing accordingly.
3. Verify lot eligibility. Before closing on any infill land, confirm lot size, zoning district, overlay status, setback compliance, and utility capacity with the City of Boise Planning & Development Services.
4. Review pre-approved plans. The City's eight pre-approved ADU plan sets eliminate custom design costs and streamline permitting. Evaluate whether a pre-approved plan fits your lot configuration before engaging an architect.

For full ADU regulations, construction standards, and permitting procedures, see the Boise ADU Guide.

Verify current standards at the City of Boise Zoning Code before any development decision.

Sources

• City of Boise ZOA25-000013 ADU Amendment · https://www.cityofboise.org/news/planning-and-development-services/2026/march/city-provides-free-adu-plans-to-help-increase-housing-options · Accessed 2026-04-22
• City of Boise Zoning Code · https://codelibrary.amlegal.com/codes/boise_id/latest/boise/0-0-0-65305 · Accessed 2026-04-22
• City of Boise Pre-Approved ADU Plans · https://www.cityofboise.org/departments/planning-and-development-services/planning/boise-zoning-code/pre-approved-adu-plans/ · Accessed 2026-04-22
• Zillow Boise Home Values · https://www.zillow.com/boise-id/home-values/ · Accessed 2025-06-30
• Idaho Legislature SB 1352 · https://legislature.idaho.gov/sessioninfo/2024/legislation/S1352/ · Accessed 2026-04-22
• Idaho Legislature SB 1354 · https://legislature.idaho.gov/sessioninfo/2024/legislation/S1354/ · Accessed 2026-04-22

For source hierarchy and confidence-level definitions, see the Boise Research Methodology.

Navigation

• Back to Boise Research Library
• Boise Land Asset Hub
• Boise ADU Guide
• Boise Infill Development Asset Hub