ADU Construction Cost in Garden City
Understand the major budget considerations for ADU construction in Garden City, including site work, utilities, and finish level.
Quick answer
Most Garden City ADU construction projects cost $90,000 to $280,000, with a typical Garden City project landing near $155,000. Garden City ADU construction costs reflect the diversity of the housing stock and the variability of site conditions in this heterogeneous market.
Garden City, ID · ADU Construction
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Typical range in Garden City: $90,000 – $280,000
Most Garden City projects: $155,000
Garden City ADU construction costs reflect the diversity of the housing stock and the variability of site conditions in this heterogeneous market. Simple garage or accessory structure conversions run $90,000 to $140,000. New detached ADUs on residential lots run $130,000 to $200,000. Live-work conversion ADUs with non-standard substrates, non-standard utility configurations, and complex permitting run $150,000 to $280,000 depending on the original structure's condition and the finish specification. Garden City's location premium supports rental rates that justify construction costs at the upper end of the range — a $200,000 ADU investment is supported by higher achievable rental rates in Garden City than in similarly priced markets in outer Canyon County.
Permit costs and review times in Garden City
Permit fees and plan-review turnaround are set by Garden City, not by the contractor, and they differ across the Treasure Valley. They belong in your budget and your schedule from the start.
- How Garden City calculates the fee
- Valuation-based (ICC Building Valuation Data or actual project cost, whichever is greater). Example base tiers: $2,000–$25,000 = $150 + $17.08 per additional $1,000; $25,000–$100,000 = $542.84 + $12.32 per $1,000. Residential plan review is 50% of the permit fee for projects over $20,000 (or $155/hour under $20,000).
- Plan-review turnaround
- Building permits require 10–15 working days to review (commercial with structural review at least 21 days). Re-submittals restart the review clock.
Figures quoted from Garden City's published scheduleDevelopment Services fee schedule (Resolution 1239-26), Feb 2026
Idaho adopts building codes by statute, so the code editions are the same statewide — the 2018 IRC with Idaho amendments and the 2023 NEC. What changes between cities is the fee formula, the review queue, and which office holds the file.
The cost of adu construction in Garden City depends on the scope of work, materials selected, complexity of the layout, condition of existing systems, and the finish level you choose. Every project is different, but understanding the major cost drivers helps you plan a realistic budget and make informed decisions about where to invest and where to save. The ranges above reflect the full spectrum of projects we complete in Garden City — from straightforward updates to comprehensive renovations with premium materials and significant structural changes.
Actual project scenarios we complete in Garden City, with the typical investment and timeline for each:
Live-Work-Create District — Accessory Structure to ADU Conversion
$105,000–$165,0003–5 monthsGarden City's live-work properties often include workshop, storage, or carport structures that can be converted to legal ADUs with appropriate permits, insulation, HVAC, kitchen, bathroom, egress windows, and utility connections. These conversions leverage existing structure and foundation while transforming a utility space into a legal, habitable residential unit. The design context of the Live-Work-Create District allows more architectural individuality than suburban residential zoning — exposed concrete floors, sealed and polished, industrial-profile windows with minimal frames, utilitarian cabinetry, and spatial configurations that reflect the workshop origins of the space are entirely appropriate in a live-work conversion ADU in ways they would not be in Meridian or Nampa. These design approaches can be executed at moderate cost while producing a result that is authentically Garden City in character and that attracts exactly the tenant this district serves.
Garden City Core Bungalow — Backyard ADU
$120,000–$195,0004–5 monthsGarden City's original residential bungalows on larger lots in the city's historic core are prime candidates for backyard ADU addition — either through conversion of an existing accessory structure or new detached construction. These ADUs serve the creative community's demand for rental housing in Garden City's most walkable, character-rich neighborhoods, and they generate some of the strongest cap rates of any Treasure Valley ADU investment due to the location premium that Garden City commands. New construction backyard ADUs in the Garden City Core are typically designed to complement the bungalow's character — Craftsman-influenced detail, wood or fiber cement siding, a covered entry that creates a sense of arrival — while incorporating the contemporary interior finishes that quality tenants expect. The combination of character and quality is Garden City's ADU signature.
Greenbelt Corridor — Premium ADU for Quality Rental Income
$140,000–$220,0004–6 monthsGreenbelt Corridor properties in Garden City command the highest rental rates in the city because of their direct access to the Boise River Greenbelt, their contemporary architectural character, and their proximity to the employment and amenity concentration of downtown Boise. ADUs in this corridor are specified at a quality level that supports premium rental rates: quality cabinetry and countertops with stone or quartz surfaces, tile shower with frameless glass enclosure, premium SPC LVP flooring, and design details that reflect the architectural quality of the surrounding development. The Greenbelt Overlay may impose design review requirements for exterior modifications that affect the corridor's visual relationship to the river — Iron Crest reviews overlay applicability for every Greenbelt Corridor ADU project before design begins.
Garden City Multigenerational ADU — Creative Family Housing Solution
$135,000–$215,0004–6 monthsGarden City's creative professional families often have specific and non-standard housing arrangement goals for multigenerational living — a parent who is also an artist needing studio space alongside living accommodation, a family arrangement where proximity is valued but shared walls are not, or a housing solution for a family member who needs independent living but benefits from the practical support of being nearby. These ADU projects are the most individually designed in Iron Crest's Garden City portfolio, reflecting the specific needs and aesthetic sensibilities of Garden City's creative families. Accessible design features — zero-threshold shower, wider doorways, grab bar blocking, lever hardware — are included for multigenerational suites intended for aging parents, built in during construction at a fraction of the cost of retrofitting after completion.
These are the factors that have the biggest impact on your ADU builder budget in Garden City. Understanding each one helps you make better decisions during the planning phase.
ADU Type (Detached vs. Conversion)
high impactA detached new-construction ADU costs significantly more than a garage conversion because it requires a new foundation, full framing, roofing, and all-new utility connections. Garage conversions leverage the existing structure.
Size (Square Footage)
high impactADUs range from 300 sq ft studios to 1,000+ sq ft two-bedroom units. Larger units cost more but provide more rental income potential and livability.
Utility Connections
high impactConnecting water, sewer, electrical, and gas to the ADU site involves trenching, new service lines, and potentially utility upgrades. Distance from the main house to the ADU affects cost.
Kitchen and Bathroom Complexity
medium impactEvery ADU needs at least a bathroom and kitchen. The finish level — basic vs. mid-range vs. premium — significantly affects the mechanical and finish costs.
Site Conditions and Access
medium impactSloped lots, limited access for equipment, rocky soil, or mature trees in the building area can increase site preparation and foundation costs.
Permitting and Impact Fees
medium impactADU permit fees, impact fees, and utility connection fees vary by jurisdiction. Some Boise-area jurisdictions have reduced or waived impact fees for ADUs to encourage construction.
Materials are one of the most controllable parts of your budget. Here is how popular options compare for ADU builder in Garden City:
| Material | Price Range | Best For |
|---|---|---|
| Concrete Slab or Stem Wall Foundation | $8,000–$20,000 | Detached ADU new construction |
| Standard Wood Framing | $12–$22 per sq ft framed | All ADU types |
| Mini-Split HVAC System | $3,500–$7,000 installed | Detached ADUs and garage conversions |
| Compact Kitchen Package | $5,000–$15,000 complete | Studio and one-bedroom ADUs |
| Matching or Complementary Siding | $5–$15 per sq ft installed | Seamless property aesthetic |
Concrete Slab or Stem Wall Foundation
$8,000–$20,000
Standard Wood Framing
$12–$22 per sq ft framed
Mini-Split HVAC System
$3,500–$7,000 installed
Compact Kitchen Package
$5,000–$15,000 complete
Matching or Complementary Siding
$5–$15 per sq ft installedGarden City's unique character, Greenbelt access, and central location make it an increasingly desirable market. Property values have risen significantly, and well-renovated homes command strong prices. The community's eclectic character means creative, design-forward remodels are valued by buyers.
Labor costs in Ada County reflect the local construction market, trade availability, and seasonal demand. Spring and summer are the busiest seasons for remodeling in the Treasure Valley, which can affect scheduling and occasionally pricing. Planning your project during the fall or winter months may provide more scheduling flexibility.
The most reliable way to understand what your specific ADU builder will cost in Garden City is to schedule an in-home consultation. During this visit, we measure the space, discuss your goals and material preferences, evaluate existing conditions, and prepare a detailed scope and estimate based on your specific project.
What to have ready for your estimate consultation:
- ✓ A general idea of your budget range
- ✓ Examples of styles and finishes you like (photos, Pinterest boards, etc.)
- ✓ Any known issues with the current space (leaks, mold, outdated systems)
- ✓ A list of must-haves vs nice-to-haves for the finished project
- ✓ Your preferred timeline for starting and completing the work
Local factors — Garden City's housing stock and typical construction eras, the climate conditions that drive material and scheduling choices, and permitting through City of Garden City Building Department — are covered in full on our Garden City page for this service, alongside 4 common project types.
ADU Construction in Garden City: housing stock, climate & permits →How much does it cost to build an ADU in the Boise area?
A detached new-construction ADU typically costs $120,000-200,000+ in the Boise area, depending on size, finish level, and site conditions. A garage conversion is typically $80,000-150,000. Costs include design, engineering, permitting, construction, and utility connections.
How much rental income can an ADU generate in Boise?
A well-built one-bedroom ADU in the Boise area can generate $800-1,500+ per month in rental income, depending on location, size, finish level, and market conditions. This income can offset or exceed the monthly cost of financing the ADU construction.
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