Boise, ID Building Setbacks & Zoning: Lot Coverage Limits (2026)
Key Facts
- Max floor area
- 70% of effective lot area
- Applies to
- lots under 3,500 sf (R-2/R-3)
- Also applies to
- substandard original lots of record
- Excluded
- below-grade floor area
- Min open space
- 200 sf/unit, 25% permeable
Summary
On Residential Small Lots under 3,500 square feet and on substandard lots of record citywide, Boise limits residential floor area to 70 percent of the effective lot area, with below-grade space excluded from the count.
Building Size: Residential floor area shall not exceed 70 percent of the effective lot area. Below grade floor area is not included.
(4) Open Space: Each unit shall have a minimum of 200 square feet of open space. This open space shall be usable and shall not include driveways or parking areas. A minimum of 25 percent of the required open space shall consist of permeable ground surface with landscaping.
(5) Public Right-Of-Way Improvement:
(a) Development on Residential Small Lots that include construction of a new dwelling unit (excluding ADUs) shall provide curb, gutter, and detached sidewalk a minimum of five feet in width that is separated by a landscape planter that is a minimum of eight feet in width. Waivers or variations to this requirement may be granted by the Planning Director based upon exceptional circumstances.
(b) Where driveways access a public street, a paved driveway apron that extends to the edge of street pavement of the roadway or alley shall be provided unless a waiver or variation on some or all of this requirement is granted by the Planning Director based upon site-specific conditions such as documented drainage problems that might result from the improvement of the roadway.
(c) Dirt or gravel strips in the front yard or undeveloped public street right-of-way shall not be permitted. Irrigated landscaping shall be provided in these areas through license agreements with ACHD. Bonding for
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: 2026 S-31: Code current through: Ord. 20-26, passed 6-9-2026).
Full Breakdown
The cap applies to new dwellings and additions on lots smaller than 3,500 square feet platted in the R-2 or R-3 zoning districts after the Development Code's effective date, and to any Substandard Original Lot of Record in the R-1A, R-1B, R-1C, R-2, or R-3 districts. Effective lot area means gross lot area minus any portion tied up by a recorded driveway or road easement. Each unit must also carry at least 200 square feet of usable open space, a quarter of it permeable ground surface, on top of the floor-area limit. Planning and Development Services checks compliance at building permit review; the standard does not apply to lots inside an approved Planned Unit Development.
Violations & Fines
Building permit applications that exceed the 70 percent floor-area limit are rejected by Planning and Development Services; building without a compliant permit can trigger a stop-work order and forced modification.
Frequently Asked Questions
What counts as "effective lot area" in Boise?
Does the 70% cap apply to every Boise house lot?
Sources & Official References
Other rules in Boise
Compare Boise to another location·View the Idaho building setbacks & zoning overview
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