ADUs · Boise, Idaho
Boise ADUs, designed and built as real homes.
Boise is one of the easiest places in Idaho to add an ADU, but every lot is different. Alleys, shared driveways, existing garages, and older homes all change what fits and what it costs. Fortis is based in Boise and builds here, on the lots and streets we know.
Have a property in mind?
What Boise’s code allows today
Under Boise’s zoning code (Accessory Dwelling Unit standards):
- Up to 900 sq ft, or the total floor area of the main house, whichever is smaller.
- Up to two bedrooms.
- One ADU per lot, unless the lot qualifies for more under the city’s incentive rules.
- It can be a new detached unit, an addition, a basement or attic conversion, or a converted garage or accessory building.
- It must meet the zone’s height and setback rules and match the main home’s materials, colors, and style.
- Only one entrance can face the front of the property, unless more already exist.
- Converting a garage can’t drop the lot below its required parking.
Idaho’s new ADU law, effective July 1, 2026, may lead Boise to update some of these limits by February 1, 2027. We confirm the current rules for your lot before design.
Here in Boise
At the 25th Street Residence, an established North End property, Fortis gut renovated the existing home and designed a detached ADU, reached by a shared driveway, that is now permit-ready.
Check your property first
Parcept, Fortis’s ADU property-feasibility tool, reviews zoning, lot conditions, existing structures, and access for Boise properties and returns a free preliminary report.
Common questions
- Do I need to live on the property?
- Boise’s ADU standards don’t require it, and the new state law bars larger cities from requiring owner occupancy.
- Do I need extra parking?
- Boise’s ADU standards don’t set a separate parking requirement, but a garage conversion can’t reduce required parking.
- Can I convert my garage?
- Yes, if the lot still meets its parking minimum and the conversion meets building code.