Bill Analyses and Ratings
Bill Information: S1353E1 – Idaho Twin Home & Duplex Zoning Mandate
Bill Summary
Senate Bill 1353 prohibits Idaho cities with populations over 10,000 from banning twin homes or duplexes in any residential zoning district where single-family homes are permitted. Cities must amend their comprehensive plans and land use regulations by February 1, 2027, to explicitly allow duplex and twin home development on any lot where a detached single-family dwelling is permitted. The bill defines a ‘twin home’ as a two-unit residential building with a shared wall where each unit is independently owned in fee simple.
The bill caps parking requirements at one off-street space per unit in qualifying locations, prohibits minimum lot size rules that would effectively exclude duplexes, and bars cities from charging higher per-unit impact fees or utility connection fees for duplexes than for single-family homes. Projects that meet established land use requirements must receive administrative approval as a matter of right — no discretionary review, no planning commission hearings — mirroring the approval process for single-family homes.
Historic districts and properties designated under Idaho Code sections 67-4607 and 67-4614 are exempt from these requirements. The bill preserves existing building codes, fire safety standards, floodplain regulations, environmental protections, and infrastructure capacity constraints. Cities retain authority to impose objective standards such as impervious coverage ratios, stormwater retention requirements, and minimum lot frontage of 25–30 feet for utility spacing.
Overall Assessment
This bill directly expands what property owners in Idaho cities can build on their land by stripping local governments of the authority to zone out duplexes and twin homes from single-family neighborhoods. Developers and property owners gain a streamlined, administrative approval path for duplex projects, eliminating the cost and uncertainty of discretionary review. Cities with populations over 10,000 face a hard deadline of February 1, 2027, to rewrite their zoning codes and comprehensive plans — an unfunded state mandate with no accompanying appropriation.
This is the engrossed version of S1353.
Rating Breakdown
ARTICLE I. Responsibility in Government (0)
The bill imposes a direct mandate on cities with populations over 10,000 to amend their comprehensive plans and land use regulations by February 1, 2027, but provides no state funding to cover the administrative, legal, and planning costs of doing so. This creates an unfunded mandate, which conflicts with the principle that the government entity mandating a program should fund its implementation. However, the bill also reduces regulatory burden by requiring administrative rather than discretionary approval, partially offsetting the fiscal concern.
ARTICLE II. Citizen Involvement in Government (0)
The bill requires cities to follow the public notice and hearing procedures of section 67-6509 when amending their comprehensive plans and zoning ordinances, preserving the existing public participation process for those amendments. However, once zoning is updated, individual duplex and twin home projects receive administrative approval as a matter of right, removing the public hearing process from project-level decisions. These two effects balance each other at the policy level.
ARTICLE III. Education (0)
This bill regulates residential zoning for twin homes and duplexes and contains no provisions related to schools, curricula, school funding, or educational policy of any kind.
ARTICLE IV. Agriculture (0)
The bill applies exclusively to residential zoning within cities with populations over 10,000 and contains no provisions affecting agricultural land, farming operations, water law, or agricultural markets.
ARTICLE V. Water (0)
While the bill preserves local authority over water and sewer infrastructure capacity constraints under Section 7(b) and allows cities to impose on-site stormwater retention standards under Section 3, it does not alter water rights, appropriation law, or water management policy.
ARTICLE VI. Natural Resources and Environment (0)
Section 7(c) explicitly preserves existing laws regarding environmental hazards, aquifer recharge zones, steep slopes, and critical habitat protections, ensuring those safeguards remain in force. The bill's subject matter is urban residential zoning, not natural resource management or environmental regulation.
ARTICLE VII. Energy (0)
The bill addresses residential zoning classifications and approval processes and contains no provisions related to energy production, energy independence, utility regulation, or energy resource development.
ARTICLE VIII. Idaho National Laboratories (0)
This bill concerns city-level residential zoning and has no connection to the Idaho National Laboratory, nuclear energy research, or technology transfer programs.
ARTICLE IX. Private Property Rights (1)
The bill directly expands what property owners can build on their land by prohibiting cities from using zoning ordinances to ban duplexes or twin homes on lots where single-family homes are allowed. Section 3 further strengthens this by guaranteeing administrative, matter-of-right approval for compliant projects, eliminating the discretionary review processes that can be used to block or delay development. Section 2(b) additionally bars minimum lot size rules designed to effectively exclude these housing types, closing a common regulatory workaround.
ARTICLE X. State and Federal Lands (0)
The bill regulates private residential development within city limits and contains no provisions addressing state land management, federal land ownership, or the transfer of public lands.
ARTICLE XI. Wildlife Management (0)
This bill addresses urban residential zoning and contains no provisions related to fish and game management, hunting, fishing, or predator control.
ARTICLE XII. Economy (1)
By requiring administrative, matter-of-right approval for duplex and twin home projects, the bill reduces the time and cost burden on small residential builders and developers who currently face discretionary review processes. Section 2(d) directly lowers the cost of building duplexes by prohibiting per-unit impact fees and utility connection fees that exceed those charged for single-family homes. Together, these provisions reduce regulatory barriers that have constrained housing supply and construction activity in Idaho's growing cities.
ARTICLE XIII. Health and Welfare (0)
The bill addresses residential zoning classifications and approval procedures. It contains no provisions related to healthcare delivery, health insurance, public health programs, or welfare services.
ARTICLE XIV. American Family (0)
The bill regulates the types of housing that can be built in residential zones and does not address marriage, parental rights, child welfare, right to life, or other family policy matters covered under this metric.
ARTICLE XV. Older Americans (0)
The bill creates zoning requirements for twin homes and duplexes in cities and contains no provisions specifically addressing the needs, services, or economic circumstances of older Idahoans.
ARTICLE XVI. Law and Order with Justice (0)
This bill concerns residential land use regulation and contains no provisions related to criminal justice, law enforcement, firearms rights, sentencing, or judicial procedures.
ARTICLE XVII. National Defense - Securing the Border (0)
The bill addresses city-level residential zoning and contains no provisions related to national defense, military affairs, veterans, or border security.
ARTICLE XVIII. Election of Judges and Idaho Supreme Court Justices (0)
This bill concerns housing zoning policy and contains no provisions related to judicial elections, court structure, or constitutional interpretation.
ARTICLE XIX. Religious Liberty (0)
The bill regulates residential land use in Idaho cities and contains no provisions that affect the free exercise of religion or religious institutions.