Boise Infill Development Guide

Cities with populations over 10,000 must allow residential development at a minimum density of 12 units per acre on tracts of 4 acres or larger. Lots may be as small as 1,400 square feet. Setback and lot-width requirements do not apply to qualifying starter-home subdivisions.

Investor implication: Enables high-density small-lot subdivisions on larger parcels, unlocking land value through unit count rather than lot size. Operators can pursue 12+ units/acre without traditional setback constraints on qualifying tracts.

Cities over 10,000 population must allow at least one accessory dwelling unit per lot. No owner-occupancy requirements. No blanket square-footage bans. HOAs cannot add new ADU restrictions without written consent of all members (existing bans remain enforceable).

Investor implication: Guarantees ADU-by-right on every residential lot statewide, removing local discretion to block ADUs. Infill builders can plan for ADU income or resale premium without zoning risk.

Boise allows up to 2 ADUs per lot. Maximum size: 900 sq ft or 70% of primary dwelling floor area, whichever is less. Junior ADUs up to 500 sq ft permitted. Alley-facing ADUs may use 3-foot rear setback. No parking required within ½ mile of frequent transit.

Investor implication: Two-ADU allowance doubles rental income potential on infill lots. Alley setback relief and transit parking exemption reduce site constraints, making narrow or transit-adjacent lots viable for ADU builds.