Boise ADU · Plain-English Answers
Boise ADU frequently asked questions
Costs, permits, the 6 pre-approved plans, build timelines, rental rules, and the rest — answered short and direct.
Cost & financing
How much does a Boise ADU cost in 2026?
Pre-approved Boise ADUs run $115k-$345k turnkey at Essential finish, depending on plan size. Smallest is the Goldfinch (280 sqft studio, from $115k); largest is the Kestrel (695 sqft 2-bed, from $245k). Final price varies by finish level (Essential / Standard / Premium) and lot conditions. Use our cost calculator for a per-plan range.
What's the cheapest pre-approved ADU plan in Boise?
The Goldfinch — 280 sqft Type A studio, from $115k turnkey. It's the smallest of Boise's six pre-approved plans and the cheapest path to a permitted ADU.
What's the most expensive pre-approved plan?
The Kestrel — 695 sqft Type D 2-bedroom, from $245k turnkey at Essential finish. It's the largest of the six and the only pre-approved 2-bedroom.
How do most Boise homeowners pay for an ADU?
Three main paths: HELOC against existing home equity, cash-out refinance, or a construction loan that converts to a permanent mortgage. See our financing guide for the full comparison.
Will an ADU pay for itself?
On a long-term rental, usually within 8-12 years on a $115k-$245k pre-approved plan in Boise. Typical 1-bed rents of $1,500-$1,800/mo on a Kingfisher (491 sqft) on a $170k Essential build = roughly 9-11% gross yield. After taxes and reserves, expect 6-8% net cash-on-cash.
Permits & zoning
Where can I build an ADU in Boise?
Most Boise residential zones (R-1A, R-1B, R-1C, and several others) allow ADUs subject to lot size minimums (typically 5,000 sqft+), setbacks (typically 5' side / 10' rear), and a 900 sqft cap on accessory dwelling size (raised from 700 under the 2023 Modern Zoning Code). Verify your specific zoning at city.boise.gov/permits before designing.
Do I have to live on the property to build an ADU?
Boise's owner-occupancy requirement was relaxed in 2023 for most ADU types — you no longer need to live on-site to rent the ADU long-term. Short-term rental (Airbnb) still requires a separate STR permit. Confirm current rules with City of Boise before relying on this.
How long does Boise ADU permitting take?
For a pre-approved plan: 3-5 weeks. For a custom plan: 7-12 weeks (extra time is design review). Pre-approved status skips the design-review step entirely, which is typically the longest portion of the timeline.
What's a 'pre-approved' ADU plan?
City of Boise pre-approved plans are designs that have already passed the city's review for code compliance, design standards, and structural soundness. There are six: Goldfinch, Waxwing, Kingfisher, Kestrel, Sandpiper, Osprey. Using one cuts permitting time by 4-8 weeks and saves $8-15k in design fees.
What are the six pre-approved ADU plans in Boise?
Goldfinch (280 sqft studio, Type A), Waxwing (396 sqft studio, Type B), Kingfisher (491 sqft 1-bed, Type C), Kestrel (695 sqft 2-bed, Type D), Sandpiper (396 sqft + garage, Type G-1), Osprey (376 sqft + garage, Type G-2). All approved by the City of Boise in 2026.
Are setbacks the same in every Boise-metro city?
No. Boise typically requires 5' side / 10' rear. Eagle requires 10' side / 15' rear. Garden City uses 5' typical setbacks but has its own development code. Each city is different — see our service-area pages for the city-by-city breakdown.
Plans & design
What's the difference between attached and detached ADUs?
Attached ADUs share a wall with the main house — typically a converted basement, addition, or upper-floor unit. Detached ADUs are stand-alone backyard buildings. Detached generally has higher rental ceiling and more privacy; attached is cheaper to build because it shares utilities and existing structure.
What's a garage conversion?
Converting an existing detached garage into a permitted ADU. Cheaper than building from scratch ($60-120k typical) because the foundation and shell exist, but limited by the original structure's dimensions and condition. Boise treats garage conversions under the same ADU rules as new construction.
Can I customize a pre-approved plan?
Finish-level customization (Essential / Standard / Premium) is straightforward and stays inside the pre-approved track. Structural changes (window placement, room layout, footprint) push the project back into custom permitting and add 4-8 weeks of design review.
What if none of the six plans fit my lot?
We also build fully custom ADUs. Custom adds 6-10 weeks to the timeline and a design fee, but lets us tailor a plan to unusual lots, specific use cases, or design preferences the pre-approved plans don't cover.
Process & timeline
How long does it take to build a Boise ADU?
Typical contract-to-keys timeline is 5-7 months: 3-5 weeks of permitting (faster for pre-approved), then 4-5 months of construction. Smaller plans don't always build faster — site work, foundation, and inspections drive most of the schedule.
Do I need an architect?
Not for a pre-approved plan — the architecture is already done. For a fully custom design, yes; we work with Boise architects routinely and can include design-build pricing in a single contract.
Who pulls the permit?
We pull the permit in your name (the homeowner's). You're the property owner of record; we're the contractor of record. Permit inspections are scheduled and managed by us throughout construction.
What happens if there's a change order?
Major scope changes (different finishes, additional rooms, structural changes) get priced as written change orders before work proceeds. Minor field adjustments inside the agreed scope don't add cost. Our fixed-price contracts are designed to minimize change orders by getting the scope right up front.
When do I pay for an ADU build?
Typical payment schedule: deposit at contract signing, then progress payments at permitting, foundation, framing/dry-in, and substantial completion. Final 10% holds until your certificate of occupancy and punch-list completion.
Living in & renting an ADU
Can I rent the ADU on Airbnb?
Boise allows short-term rental of an ADU subject to a separate STR (short-term rental) permit. The 2023 owner-occupancy change relaxed long-term rental rules; short-term still has additional requirements. Confirm current STR rules with City of Boise before counting on Airbnb income.
What rent can I get for a Boise ADU?
Long-term rents in Boise (2026): studios $1,400-$1,700/mo; 1-bedrooms $1,500-$1,800/mo; 2-bedrooms $1,900-$2,400/mo. Treasure Valley suburbs (Meridian, Eagle) trend $100-$200 higher; Caldwell and Kuna trend $100-$200 lower. Source: Apartment List + Zillow ZHVI Treasure Valley comps, 2026.
Can my parent live in the ADU?
Yes — a multigenerational ADU is one of the most common Boise use cases. The Kingfisher (1BR) and Kestrel (2BR) are the most common picks for aging parents. Plan for grab-bar blocking, zero-threshold showers, lever hardware, and 36-inch doors at build time; retrofitting is more expensive.
Can I work from the ADU?
Yes — Boise zoning allows home occupations in an ADU subject to typical home-business rules (no walk-in clientele in residential zones, etc.). The Goldfinch (280 sqft studio) is the cheapest detached home office; the Waxwing or Kingfisher are roomier for full-time work.
Still have questions?
We answer every email within one business day. Or call (208) 297-2036.