Comparison · Permitted vs Unpermitted
A backyard cottage ADU is a permanent, permitted, financeable dwelling Boise will let you rent. A tiny house on wheels is not. Here's the legal divide, the cost math, and when a tiny house actually makes sense.
A backyard cottage ADU is a permanent, code-compliant dwelling that Boise will permit, finance, insure, and let you rent. A tiny house on wheels (THOW) is not legal as a primary or accessory dwelling on a Boise residential lot — it's classified as a recreational vehicle. A tiny house on a permanent foundation can be permitted IF it meets full International Residential Code (IRC), but most stock tiny-house designs don't. For roughly 90% of Boise homeowners, the backyard cottage ADU is the correct path.
Construction by Iron Crest Remodel — Idaho contractor license RCE-6681702.
The legal divide
"Tiny house" is a marketing term, not a legal one. Boise's permit system reads structures three ways, and the difference between them is the difference between a financeable rental and an RV you can't legally live in.
A permanent-foundation accessory dwelling unit built to the International Residential Code (IRC) and Boise's Modern Zoning Code. Boise will permit, inspect, and issue a certificate of occupancy. Eligible for the city's pre-approved plan program (up to 900 sq ft).
Can be permitted only if the design meets full IRC residential standards — minimum ceiling height (7 ft in habitable rooms), legal egress windows, fixed stairs to lofts, smoke + CO alarms, energy code. Most stock tiny-house designs don't qualify out of the box. A custom-built, IRC-compliant tiny house is effectively a small ADU.
Classified as a recreational vehicle under Idaho Code Title 49 (motor vehicles) and ANSI A119.5. Cannot be your primary or accessory dwelling on a Boise residential lot. Some districts permit parking; none permit occupancy as a permanent residence. Boise treats a THOW the same as an RV or travel trailer.
Code references: Boise Modern Zoning Code §11-06 (ADU standards, 900 sq ft cap effective Dec 1, 2023), 2018 International Residential Code (habitable-room standards), Idaho Code Title 49 (motor vehicles and RV classification), and ANSI A119.5 (park model RV / THOW construction standard).
Thirteen factors most shoppers weigh, with honest numbers for each. Cottage column reflects Boise's pre-approved plan pricing (Iron Crest's published pricing grid). Tiny-house ranges from industry sources including tinyhomebuilders.com, Cavco park models, and Tumbleweed Tiny House Company's published price lists.
| Factor | Backyard cottage ADU | Tiny house (THOW or stock) |
|---|---|---|
| Legal status as dwelling | Permitted accessory dwelling unit (ADU) | THOW classified as RV; not a legal dwelling on a residential lot |
| Permit path | Boise building permit + ADU review (3-5 weeks on pre-approved plans) | THOW: no dwelling permit available. Permanent-foundation tiny house: same path as ADU if IRC-compliant |
| Code compliance | Full IRC + 2018 IECC + Boise residential amendments | THOW built to ANSI A119.5 (RV standard), not residential code |
| Foundation | Engineered permanent concrete foundation required | THOW on wheels with hitch; permanent-foundation version requires engineered foundation |
| Minimum size | No code minimum; pre-approved plans start at 280 sq ft (Goldfinch) | Typically 100-400 sq ft by industry convention |
| Maximum size | 900 sq ft or 50% of primary dwelling living area, whichever is less | <400 sq ft by industry definition (tinyhomebuilders.com); >400 sq ft is just a small house |
| Cost range (turnkey) | $115k-$345k (Boise pre-approved plans, Essential to Premium finish) | $30k-$120k for the unit; site work, hookups, foundation extra if applicable |
| Financing eligibility | HELOC, construction loan, cash-out refi, renovation loan — all available | RV loan (8-12% APR, 10-15 year term) for THOW; chattel loan for unaffixed units |
| Insurance | Homeowners + dwelling policy | RV / personal-property policy for THOW; homeowners only if affixed to permitted foundation |
| Rental potential | Legal long-term rental (no owner-occupancy required after 2023) | THOW occupancy not permitted in Boise residential zones |
| Resale impact | Appraises as a separate dwelling unit; typically adds value > construction cost | THOW depreciates as a vehicle; not counted in real estate appraisal |
| Build time | 5-7 months on pre-approved plans, 7-9 months custom | 8-16 weeks factory-built; 6-12 months DIY custom |
| Utility hookups | Permanent permitted water, sewer, and electrical connections | RV pedestal at best in residential zones; no permanent sewer/water tie-in for a THOW |
Tiny houses aren't a fraud — they're a real product with real use cases. Two situations where a THOW is the right tool. Note: neither of these is a substitute for an ADU on a Boise residential lot.
Idaho County and Boise County rural parcels (outside Boise city limits) have different rules. A THOW or small cabin can work as a recreational use on land that's zoned for it — not as a primary dwelling on a Boise residential lot.
Private campgrounds and licensed RV parks in the Treasure Valley accept THOWs the same way they accept travel trailers. Short stays, hookups by the night or month, no residential occupancy claim.
If your goal is income, equity, or housing a family member on your Boise property, a THOW won't deliver any of those legally. That's not the tiny-house industry's fault — it's a category mismatch.
Honest economic logic, not a sales argument. Most homeowners who shop tiny houses first move to an ADU once they price out the real costs of legal occupancy, financing, and resale.
An ADU shows up on title, in the appraisal, and on tax records as a real dwelling. A THOW sits in the same legal lane as a parked travel trailer — owners get cited, displaced, or quietly pushed out when neighbors complain.
HELOC and renovation loans on an ADU run 7-9% APR over 20-30 years. RV financing on a THOW runs 8-12% over 10-15 years. The monthly carry difference compounds fast on the same dollar amount.
Standard homeowners policies cover a permitted ADU as part of the dwelling. THOWs require specialty RV policies, and most carriers won't write a policy for a THOW used as a primary residence on a residential lot.
A permitted detached ADU typically appraises at or above construction cost in Boise's current market. A THOW is a depreciating asset — counted as personal property at sale, not real property.
On day one, a tiny house looks cheaper. A factory-built THOW from a recognized brand runs $30,000-$80,000; custom builds reach $80,000-$120,000+ (tinyhomebuilders.com, Tumbleweed, Cavco park-model price lists, 2024-2026). A pre-approved Boise backyard cottage runs $115,000 (Goldfinch, 280 sq ft, Essential finish) up to $345,000 (Kestrel, 695 sq ft, Premium) turnkey at Iron Crest pricing.
Over 10 years, the math flips. A 491 sq ft Kingfisher at $170k turnkey rents for $1,500-$1,800/mo in 2026 Boise — call it $1,650 average. That's $19,800/year gross, or roughly $198,000 over 10 years before appreciation, minus operating costs. Appraisers credit the ADU at sale; HELOC and refi financing options price like real estate, not like an RV loan.
A THOW generates no legal rental income on a Boise residential lot, doesn't lift the property's appraisal, and depreciates the same way a travel trailer depreciates. The "cheaper" option in year one is usually the more expensive option in year ten.
Not as a dwelling. A tiny house on wheels (THOW) is classified as a recreational vehicle under Idaho Code Title 49 and the ANSI A119.5 standard. Boise residential zones permit ADU dwellings on permanent foundations — they don't permit RVs to be lived in as a primary or accessory residence. You may be able to park a THOW on the lot under RV-storage rules, but occupancy isn't allowed. The legal alternative is a backyard cottage ADU, which Boise raised to a 900 sq ft maximum in the 2023 Modern Zoning Code update.
Boise's Modern Zoning Code doesn't set a hard minimum square footage for an ADU. The smallest pre-approved plan is the Goldfinch (Type A) at 280 sq ft — a full studio with kitchen, bathroom, and a single open living space. That's also the cheapest legal, permitted, code-compliant ADU in Boise, starting around $115k turnkey at Essential finish.
Only if it's on a permanent foundation and titled as real property with the land — which means it has to meet IRC residential code, in which case it's an ADU, not a tiny house in the traditional sense. THOWs are financed through RV loans (typically 8-12% APR, 10-15 year terms) or chattel/personal-property loans, never a standard mortgage. By contrast, a permitted ADU is financeable through HELOC, cash-out refinance, construction loan, or renovation loan at standard mortgage rates.
Functionally yes, if it meets the same code. Boise will permit a tiny house on a permanent foundation as long as the structure satisfies the full IRC: minimum 7-foot ceiling in habitable rooms, legal egress windows in any sleeping room, fixed stairs (not a ladder) to any loft used as a bedroom, smoke and CO detection, and current energy code. Most stock tiny-house designs from off-the-shelf manufacturers don't meet all of these without modification. A custom build to IRC effectively is a small ADU — at which point you may as well use one of Boise's six pre-approved plans for the 3-5 week permit fast track.
A permitted ADU on a permanent foundation adds appraised value — typically at or above construction cost for the Treasure Valley market in 2026, per local builder data. A tiny house on wheels does not. THOWs are personal property, not real property, and don't transfer with the land at sale. Appraisers won't credit a THOW in the home's value the way they credit a permitted detached cottage.
Yes — the Goldfinch is a 280 sq ft pre-approved Boise ADU plan that delivers the tiny-house feel (single open living space, efficient kitchen, full bath) with full legal status, permanent foundation, real financing, and a standard homeowners insurance policy. See the Goldfinch plan page for layout and pricing.
Backyard cottages in Boise
The commercial cottage builder page — six pre-approved plans, fixed pricing.
The Goldfinch (280 sq ft)
The smallest legal pre-approved ADU in Boise — the closest cottage to a tiny-house footprint.
All 6 pre-approved plans
Goldfinch, Waxwing, Kingfisher, Kestrel, Sandpiper, Osprey — full plan catalog.
Boise ADU laws in 2026
Zoning, setbacks, owner-occupancy, and the rules that shape what you can build.
The Boise ADU pillar guide
Start-to-finish reference for homeowners considering an ADU.
Boise ADU cost in 2026
Plan-by-plan pricing, finish tiers, and what actually drives the range.
Detached ADU vs garage conversion
Sibling comparison — when each path wins, with full feature matrix and cost deep dive.
Pre-approved vs custom ADU plans
Six city plans vs bespoke design — timeline, cost, lot flexibility, and what you can change.
Free Lot Check · 24-Hour Response
A 280 sq ft Goldfinch ADU is the closest legal cottage to a tiny-house footprint — and it permits, finances, insures, and appraises like a real dwelling. Start with the free lot check. Or call (208) 297-2036.
