Boise · Treasure Valley · Backyard Homes
Standalone backyard homes built on their own footprint — top rental income, real privacy for both households, and the strongest resale value of any ADU configuration. Pre-approved plans available.
A detached ADU is a fully separate, permitted dwelling built on the same lot as your main house — its own walls, roof, entrance, kitchen, and bathroom. Sometimes called a backyard home, granny flat, or casita. In Boise it's the most common ADU configuration because it delivers the most privacy, the highest rent, and the strongest resale lift. Unlike an attached ADU or garage conversion, a detached ADU is built ground-up as a standalone building, with a fresh foundation and fresh utility runs. In Boise's R-1A and R-1B zones, detached ADUs are allowed by right up to 900 square feet of conditioned living area, with 5-foot side and 10-foot rear setbacks on lots of at least 5,000 square feet. Most Boise lots qualify without a variance — and with a pre-approved plan, permits issue in 3–5 weeks instead of 10–12.
Both configurations are legal in Boise. Both can be permitted under the same code path. The choice usually comes down to privacy, rent ceiling, and how much the asset reads as a standalone home at appraisal.
A detached ADU sits on its own footprint with its own walls, its own entrance, and its own outdoor area. Tenants don't share a wall with you, and you don't hear them. The number-one reason Boise homeowners pick detached over attached.
Detached units rent for more than attached suites of the same size in Boise — often $200-400 more per month. Renters pay a privacy premium, and detached units appeal to long-term tenants who want a stand-alone home rather than a basement apartment.
Appraisers in Ada County treat permitted detached dwellings as a separate, full-utility structure. That typically lifts your appraisal more than a converted basement or attached suite of the same square footage. The asset reads as a second home, not a remodel.
Because the new building isn't tied to the existing home's roofline, walls, or utilities, you have far more layout flexibility. Different roof pitch, different siding, different orientation — whatever works best for the lot, the sun, and the privacy you want.
City of Boise's pre-approved set includes four standalone detached options (Goldfinch, Waxwing, Kingfisher, Kestrel) plus two studio-plus-garage combo plans (Sandpiper, Osprey) that are detached from the main house. All six skip 4-8 weeks of design review.
Type A · 280 sqft · Studio
The smallest pre-approved Boise ADU plan — a 280 sq ft studio that fits the tightest lots and the cleanest budgets.
From $115k →
Type B · 396 sqft · Studio
A 396 sq ft studio with more breathing room — full living, kitchen, and bath in a thoughtfully laid-out single space.
From $135k →
Type C · 491 sqft · 1BR
Boise's pre-approved 491 sq ft one-bedroom — separate bedroom, full kitchen, full living room, ready to permit.
From $170k →
Type D · 695 sqft · 2BR
The largest pre-approved Boise plan — a 695 sq ft two-bedroom that lives like a small house.
From $245k →
Fixed-price, turnkey numbers. Includes site work, foundation, framing, MEP rough-in, insulation, drywall, finishes, and paint. Excludes furniture, premium appliance upgrades, and landscaping.
| Plan | Size | Starting Price | Notes |
|---|---|---|---|
| Goldfinch (Type A) | 280 sqft | From $115k | Smallest pre-approved detached studio. Tightest budget, fastest build. |
| Kingfisher (Type C) | 491 sqft | From $170k | Most popular detached 1BR for long-term rental in Boise. |
| Kestrel (Type D) | 695 sqft | From $245k | Largest pre-approved detached plan — true 2BR with full living space. |
| Custom detached | ~600 sqft | $200k-$300k | Fully custom layout when the pre-approved set doesn't fit your lot or use case. |
Want a real number for your address? Try the cost calculator or get a free 24-hour estimate.
These are the four rules that come up on almost every Boise detached ADU project. Lot-specific overlays can change them — we verify your zoning during the free estimate before any drawings start.
In most Boise R-1 zones a detached ADU needs 5 feet from side property lines and 10 feet from the rear alley or property line. Lot-specific overlays can change this — we verify your address before we draw.
City of Boise caps detached ADUs at 900 square feet of finished living area under the 2023 Modern Zoning Code — raised from 700 sq ft. The largest pre-approved plan (Kestrel at 695 sqft) is well under the cap. Garage square footage on a Sandpiper or Osprey plan does not count toward this cap.
Boise zoning requires the parent lot to be at least 5,000 square feet to add a detached ADU. Smaller infill lots may still qualify under specific overlays — we can pull your zoning before you commit.
Boise typically requires one additional off-street parking space for a detached ADU on top of the parking already required for the main house. Driveway, pad, or carport — it doesn't have to be a garage.
Boise's residential code caps detached ADUs at 900 square feet of conditioned living space under the 2023 Modern Zoning Code — raised from 700 sq ft. The Kestrel pre-approved plan at 695 sqft sits well under the cap. Custom designs up to 900 sq ft are possible — we verify the maximum during the free estimate.
Yes. Boise removed the owner-occupancy requirement in 2023, so you can rent both the main house and the detached ADU as long-term rentals. Short-term rental rules vary by neighborhood and overlay — verify with the City of Boise short-term rental program before you commit to STR-only economics.
Pre-approved detached plans run from $115k turnkey for the 280 sqft Goldfinch up to $245k for the 695 sqft Kestrel. Custom detached ADUs typically run $200k-$345k depending on size, finish level, and lot conditions. Site work, permits, foundation, framing, MEP, and finishes are all included in the fixed price.
Boise allows shared utility services with the main house in most cases — the ADU runs off your existing water, sewer, and electric with sub-metering or a single bill. If you want truly independent metering for a rental, separate services are an option but add $5k-$15k in trenching and connection fees. Most landlords skip it.
Mature trees affect siting more than anything else on a Boise lot. Boise has tree preservation requirements in some zones, and root zones complicate foundation placement. We walk the lot during the free estimate, identify which trees stay, which need an arborist sign-off, and which truly limit where the ADU can sit.
Free Lot Check · 24-Hour Response
Start with a free lot check covering plan fit, setbacks, utilities, and a recommended next step. Or call (208) 297-2036 to talk it through.
