Aging parents
Privacy + proximity. A backyard cottage lets parents stay independent — own kitchen, own bath, own front door — while you're still steps away. Long-term, it costs far less than five years of assisted living.
Boise · Treasure Valley · Backyard Cottages
Backyard cottage builder in Boise
Permitted, code-compliant backyard cottages — guest houses, in-law cottages, casitas, and small detached homes — built on the same lot as your main house. From $115k turnkey on Boise's pre-approved plans.
Backyard cottages, guest houses, and ADUs — explained
A backyard cottage is a small, permitted, fully-functional secondary dwelling on the same lot as your main house. Zoning calls them ADUs — accessory dwelling units. Homeowners call them backyard cottages, guest houses, in-law cottages, casitas, or granny flats. Same thing. In Boise, they're allowed in most residential zones up to 900 sq ft of finished living area (raised from 700 in 2023), with 5-foot side and 10-foot rear setbacks on lots of at least 5,000 sq ft.
The City of Boise published six pre-approved cottage plans in 2026 — four standalone detached ( Goldfinch, Waxwing, Kingfisher, Kestrel ) plus two studio + garage combos. Building one of these skips 4–8 weeks of design review at the city and saves $8–15k in architecture fees.
Who backyard cottages are good for
Six common use cases. Most projects we build mix two or three — "for my mother now, rental income later" is one of the most common briefs we hear.
Adult children
Adult kids back from college, in graduate programs, or saving for a down payment. A cottage gives them a real address and you a backstop. Converts to rental cleanly later.
Rental income
Boise long-term rents on a 491 sq ft 1-bedroom run $1,500-$1,800/mo in 2026. A pre-approved cottage at $170-200k turnkey delivers roughly a 9-11% gross yield.
Guest space
Family visits, friends staying for a wedding, holiday traffic — a guest cottage is the comfortable solution that doesn't take over your main house for a week at a time.
Home office
A real, code-compliant office 30 feet from the back door — separate utilities, separate climate, full bathroom for long workdays. Permits as a residential ADU, doesn't require commercial review.
Property value
Permitted detached cottages appraise as separate dwelling units in Boise. Adding one typically lifts property value by more than the construction cost, especially in established neighborhoods.
Detached cottage options we build
Four pre-approved detached plans plus full custom. Each plan has a different sweet spot — pick by use case first, lot fit second, finish budget third.
280 sq ft · Studio
The Goldfinch
The smallest pre-approved Boise ADU plan — a 280 sq ft studio that fits the tightest lots and the cleanest budgets.
From $115k →
396 sq ft · Studio
The Waxwing
A 396 sq ft studio with more breathing room — full living, kitchen, and bath in a thoughtfully laid-out single space.
From $135k →
491 sq ft · 1BR
The Kingfisher
Boise's pre-approved 491 sq ft one-bedroom — separate bedroom, full kitchen, full living room, ready to permit.
From $170k →
695 sq ft · 2BR
The Kestrel
The largest pre-approved Boise plan — a 695 sq ft two-bedroom that lives like a small house.
From $245k →
Backyard cottage cost ranges (2026)
Turnkey, fixed-price ranges from Essential finish. Includes site work, foundation, framing, MEP, insulation, drywall, finishes, standard appliances, and permits. Excludes furniture, premium appliance upgrades, and landscaping beyond rough grade.
| Cottage type | Plan | Starting price | Notes |
|---|---|---|---|
| Studio cottage (280 sq ft) | Goldfinch (Type A) | From $115k | Smallest pre-approved Boise cottage. Single occupant, fits tight lots. |
| Studio cottage (396 sq ft) | Waxwing (Type B) | From $135k | More breathing room, defined sleeping zone, real kitchen. |
| 1-bedroom cottage (491 sq ft) | Kingfisher (Type C) | From $170k | Most popular cottage — walled bedroom, separate living, full kitchen. |
| 2-bedroom cottage (695 sq ft) | Kestrel (Type D) | From $245k | Largest pre-approved cottage and the only 2-bedroom option. |
| Custom backyard cottage | Custom design | $200k-$350k | When pre-approved plans don't fit lot, slope, view, or HOA requirements. |
Lot fit and access considerations
Four factors decide whether a cottage fits your specific lot and what it'll cost to build. The lot check verifies each one against your parcel.
Buildable envelope
After 5-foot side and 10-foot rear setbacks, your buildable area determines which cottage footprints fit. A 25x25 ft envelope holds a Goldfinch easily; a Kestrel needs more.
Access for construction
Crane access through narrow side yards adds cost. Alley-loaded lots are the easiest. Front-only lots with mature trees require careful crane routing or hand-framing.
Existing trees
Boise has tree-preservation rules in some zones. Mature trees affect siting more than any other natural feature — root zones complicate foundations, drip lines affect roofing setbacks.
Slope and drainage
Flat suburban lots are the cheapest. Sloped lots may need retaining or stepped foundations. Foothills lots trigger hillside review and add 4-8 weeks at the city.
For the full feasibility framework, see our ADU feasibility guide or the ADUs for aging parents article.
Backyard cottage FAQs
What's the difference between a backyard cottage and an ADU?
Functionally, none. A backyard cottage is the homeowner-friendly term for a detached ADU — a small, permitted, secondary dwelling on the same lot as the main house. The city calls them ADUs (accessory dwelling units) in its zoning code, but homeowners often search for them as backyard cottages, guest houses, casitas, in-law cottages, or granny flats. They're the same thing.
How big can a backyard cottage be in Boise?
Boise's residential code caps any accessory dwelling at 900 sq ft of finished living area under the 2023 Modern Zoning Code — raised from 700 sq ft. The largest pre-approved plan — the Kestrel — is 695 sq ft, well under the cap. Custom plans up to the 900 sq ft cap are possible but skip the pre-approved fast track.
Do I need to live on the property to build a backyard cottage?
Not anymore. Boise removed the owner-occupancy requirement in 2023, so you can build a backyard cottage on a property you own and rent both the main house and the cottage. Some surrounding cities (Eagle, certain Meridian zones) still expect owner-occupancy — we verify for your specific address before contract.
How much does a backyard cottage cost to build in Boise?
Pre-approved cottages run $115k turnkey (Goldfinch, 280 sq ft, Essential finish) up to $345k (Kestrel, 695 sq ft, Premium finish). Most homeowners land in the $170-245k range with the Kingfisher or Kestrel at Standard finish. Custom backyard cottages typically run $200-350k depending on size, finish, and lot conditions.
What's the rental yield on a Boise backyard cottage?
Roughly 9-11% gross on a Standard-finish Kingfisher (491 sq ft 1-bedroom) at $170k turnkey and $1,500-$1,800/mo rent. Net yield is typically 1.5-3 percentage points lower after tax, insurance, vacancy, and maintenance. Long-term rentals deliver more stable income; short-term (STR) rentals require an additional Boise permit and operational overhead.
Can a backyard cottage work for aging parents?
Yes — it's one of the most common reasons Boise homeowners build. The Kingfisher (491 sq ft, 1 BR) and Kestrel (695 sq ft, 2 BR) are the most popular plans for this use case. Add grab-bar blocking in the framing, a zero-threshold curbless shower, lever hardware on doors, and 36-inch interior doors at build time — all four together add about $4-7k and make the unit accessibility-ready for life.
Can I customize a backyard cottage to match my main house?
Finish-level customization (cabinets, counters, flooring, paint, fixtures) is fully open on pre-approved plans. Exterior elevations are locked. If your goal is exact architectural matching to the main house, that usually means custom design — adds $8-15k in architecture fees and 6-10 weeks of permitting.
What's the first step?
The free lot check. Submit your address and what you're hoping to build (or 'not sure' is fine). We check zoning, lot size, setbacks, easements, and pre-approved plan fit, then come back with a written summary and recommended next steps. No commitment, no fee, no follow-up sales pressure if it's not the right fit.
Free Lot Check · 24-Hour Response
Ready to plan your backyard cottage?
Two-minute lot check. We come back with the cottage plans that actually fit your lot, cost ranges, and recommended next steps.