Small-format new build on large post-war lots. ZOA25-000013 (2026) permits 2 ADUs per lot up to 900 sq ft. Idaho SB 1352 expands compact-lot density at 12 units per acre on 4+ acre tracts effective July 2026.
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ADU reforms effective February 2026 removed most of the friction that made Boise ADU projects uneconomic pre-2024. The city now allows up to two ADUs per lot, eliminated owner-occupancy requirements, and provides eight pre-approved plans that bypass design review. Builders who can execute on these plans at speed have a structural advantage.
Lot-split economics in Boise depend heavily on utility hookup costs and street frontage requirements. A minor land division that avoids full subdivision review can pencil at significantly lower density than a full plat, but only if the parent parcel already has adequate infrastructure capacity.
The Bench and SE Boise neighborhoods offer the cleanest infill execution path in Boise. Large R-1 lots, minimal historic overlay interference, and strong rental absorption for both ADUs and duplexes. Builders focused on speed and repeatability should prioritize these submarkets.
Idaho's SB 1354 and SB 1352 preempt local ADU restrictions statewide, but Boise's local code is already more permissive than the state floor. Builders operating in Boise should reference city code first; the state statutes matter more in restrictive jurisdictions like Eagle or Star.
Pre-approved ADU plans eliminate design review but do not eliminate the need for site-specific engineering. Utility capacity, setback compliance, and drainage still require professional review. Builders who treat pre-approved plans as plug-and-play without site diligence will encounter costly delays.
Relevant code
Code references active as of publication. Verify current standards at the official source before any development decision.
Idaho SB 1354 preempts local ADU restrictions statewide, establishing a state floor for ADU permissiveness.
Investor implication: State preemption matters more in restrictive jurisdictions; Boise's local code already exceeds state minimums.
Verify at Idaho Legislature SB 1354 →ZOA25-000013 ADU reforms allow up to two ADUs per lot, eliminate owner-occupancy requirements, and provide pre-approved plans.
Investor implication: Removes most regulatory friction that made ADU projects uneconomic pre-2024; builders can now execute at speed using pre-approved plans.
Verify at City of Boise ZOA25-000013 ADU Amendment →ADU reforms effective February 2026 allow up to two ADUs per lot, eliminate owner-occupancy requirements, and provide eight pre-approved plans that bypass design review.
Investor implication: Structural advantage for builders who can execute pre-approved plans at speed.
Verify at City of Boise ZOA25-000013 ADU Amendment →Idaho SB 1352 further clarifies statewide ADU preemption and prohibits local governments from imposing owner-occupancy requirements.
Investor implication: Reinforces state-level ADU permissiveness; Boise already compliant.
Verify at Idaho Legislature SB 1352 →Risks & constraints
Named risk patterns for this asset class. Underwrite against them.
North End and East End historic overlays impose design review requirements that can add 60–90 days to project timelines and require architectural modifications that increase construction costs. Pre-approved ADU plans do not bypass historic design review.
Utility hookup costs for ADUs vary widely depending on existing service capacity. A lot with adequate water/sewer capacity may incur $5K–$10K in hookup fees; a lot requiring main upsizing or new service laterals can exceed $30K. This cost is not discoverable until engineering review.
Lot-split and duplex projects often require assembling adjacent parcels to achieve economic density. Multi-owner assemblages introduce title risk, holdout risk, and extended acquisition timelines. Single-parcel infill projects are faster but may not support target returns at current land prices.
Idaho's statewide ADU preemption statutes (SB 1354 and SB 1352) took effect in 2024 but local jurisdictions are still updating their codes. Boise's code is already compliant, but builders operating across multiple Treasure Valley cities should verify local adoption status before relying on state preemption. Official sources: https://legislature.idaho.gov/sessioninfo/2024/legislation/S1354/ and https://legislature.idaho.gov/sessioninfo/2024/legislation/S1352/
Renew represents builders and developers across all Boise infill asset types. We source criteria-matched acquisitions and private-sale representations for lots, underwrite ADU and duplex projects with the same rigor we apply to our own capital, and provide representation through entitlement and construction. Direct builder-to-broker contact.
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