ADU Construction in Garden City, ID
From detached guest houses to garage conversions — we handle zoning research, design, permitting, and full construction of accessory dwelling units.
Build an ADU that adds usable space, flexibility, and long-term property value.
Licensed general contractor with ADU-specific experience in IdahoIn-depth knowledge of local ADU zoning rules across Boise-area jurisdictionsFull architectural design and engineering includedComplete permitting management from application through certificate of occupancy
An ADU (Accessory Dwelling Unit) is a self-contained living space on the same lot as an existing home. ADUs have become increasingly popular in the Boise area as housing demand has grown, zoning rules have evolved, and homeowners have recognized the financial and lifestyle benefits of adding a separate living unit to their property. ADU types include detached new construction (a standalone building on the lot), garage conversions (converting an existing garage into living space), attached additions (building a unit that shares a wall with the main home), and basement conversions (converting a finished or unfinished basement into a separate unit with its own entrance). Every ADU project requires careful navigation of local zoning rules, setback requirements, utility connections, parking requirements, and building code compliance. The design must balance livability, code compliance, construction cost, and long-term value. A well-built ADU adds $100,000+ in property value while generating $800-1,500+ per month in rental income in the Boise market.
Garden City homeowners pursue adu construction for a variety of reasons. Here are the most common situations we see:
- ✓Homeowners who want rental income from a detached or attached unit on their property
- ✓Families who need a guest house, in-law suite, or multigenerational living space
- ✓Remote workers or creatives who want a separate studio, office, or workshop space
- ✓Property investors who want to increase property value and utility with an ADU
- ✓Homeowners who want housing flexibility — rent now, use for family later, or vice versa
Not every adu builder project is the same. Here are the most common project types we complete in Garden City:
Detached ADU (New Construction)
A standalone structure built on your property — typically 400-1,000 square feet with a bedroom, bathroom, kitchen, and living area. This is the most popular ADU type and offers the most design flexibility.
Garage Conversion ADU
Convert an existing attached or detached garage into a living space. Includes insulation, drywall, flooring, plumbing, electrical, HVAC, kitchen, and bathroom installation within the existing structure.
Attached ADU Addition
Build an ADU that shares one or more walls with the main home but has its own entrance, kitchen, bathroom, and living space. Similar to a home addition but designed as an independent unit.
Basement ADU Conversion
Convert an existing basement into a separate dwelling unit with its own entrance, kitchen, bathroom, and living area. Requires egress windows, fire separation, and independent utility metering in most jurisdictions.
Garden City has a diverse and eclectic housing stock — from 1950s river cottages to modern townhomes. Properties tend to be smaller than other Treasure Valley cities, making space-efficient design a priority.
1950s–1970s (cottages, older homes)
Small homes and cottages near the river. These often need comprehensive updates — plumbing, electrical, insulation, and finishes — but offer character and location value.
1990s–2010s
A mix of standard residential construction and townhome development.
2010s–present
Modern townhomes, infill development, and adaptive-reuse properties. These tend to have modern systems with design-focused upgrade opportunities.
Common issues in Garden City homes
- •Compact floor plans requiring space-efficient design solutions
- •Older plumbing and electrical in 1950s-1970s homes
- •Smaller lots with limited expansion potential
- •Mixed-use zoning that affects project planning
- •River proximity moisture considerations for some properties
Material selection affects the look, durability, and cost of your adu builder. Here are the most popular options we install in Garden City:
Concrete Slab or Stem Wall Foundation
$8,000–$20,000Most detached ADUs in Idaho use a concrete slab-on-grade or stem wall foundation depending on lot conditions, frost depth, and plumbing requirements. Garage conversions may use the existing slab with modifications.
Best for: Detached ADU new construction
Standard Wood Framing
$12–$22 per sq ft framed2x4 or 2x6 wood framing for walls, with trusses for the roof. ADU framing follows the same building codes as primary residences, including insulation requirements, fire separation, and structural standards.
Best for: All ADU types
Mini-Split HVAC System
$3,500–$7,000 installedThe most common heating and cooling solution for ADUs. A ductless mini-split provides efficient heating and cooling with a small exterior compressor and one or two interior wall units. No ductwork required.
Best for: Detached ADUs and garage conversions
Compact Kitchen Package
$5,000–$15,000 completeADU kitchens need to be efficient. A compact kitchen typically includes a 24-inch range, apartment-size refrigerator, single-bowl sink, and upper and lower cabinets — all designed to maximize function in a smaller footprint.
Best for: Studio and one-bedroom ADUs
Matching or Complementary Siding
$5–$15 per sq ft installedThe ADU exterior should complement the main home. Options include matching the existing siding exactly, using a contrasting but compatible material, or using a modern material like board-and-batten or metal panel for a contemporary look.
Best for: Seamless property aesthetic
Here is how a typical adu builder project works from first contact to final walkthrough:
1
Zoning and Feasibility Research
We research your property's zoning designation, lot size, setback requirements, maximum ADU size allowed, parking requirements, and any HOA restrictions. Not every lot qualifies for an ADU, so this step is critical before investing in design.
2
Concept Design and Budget Planning
Based on feasibility findings, we develop a concept design including floor plan, placement on the lot, utility connection points, and exterior style. You receive a preliminary budget range to confirm the project is viable.
3
Architectural Plans and Engineering
Detailed architectural plans are prepared including floor plans, elevations, structural engineering, mechanical systems, and site plan. These plans must meet local building codes and will be submitted for permit review.
4
Permitting and Utility Coordination
We submit plans for permit review, coordinate utility connections (water, sewer, electrical, gas), and manage any required inspections or reviews. ADU permitting can take 4-8 weeks depending on the jurisdiction.
5
Site Preparation and Foundation
Excavation, grading, utility trenching, and foundation work. For detached ADUs, this typically means a new concrete foundation. Garage conversions may require foundation modifications.
6
Construction (Framing through Finish)
Complete construction including framing, roofing, siding, windows, insulation, drywall, flooring, kitchen, bathroom, HVAC, electrical, plumbing, and all finish work. The ADU is built to the same code standards as a primary residence.
7
Final Inspection and Certificate of Occupancy
All required inspections are passed, the certificate of occupancy is issued, and the ADU is ready for use. We provide a complete walkthrough and all warranty documentation.
Here is what to expect for project duration when planning a adu builder in Garden City:
| Phase | Duration | Details |
|---|---|---|
| Zoning Research and Feasibility | 1–2 weeks | Confirm the property qualifies for an ADU under current zoning, identify setback and size constraints, and determine utility connection feasibility. |
| Design and Engineering | 4–8 weeks | Architectural plans, structural engineering, site plan, and mechanical design. ADU designs must meet full building code requirements. |
| Permitting | 4–8 weeks | Plan review, permit issuance, and any required revisions. ADU permitting timelines vary by jurisdiction in the Treasure Valley. |
| Site Work and Foundation | 2–4 weeks | Excavation, utility trenching, foundation pour, and curing. Weather-dependent in Idaho, especially during winter months. |
| Framing, Roofing, and Mechanical | 4–8 weeks | Framing, roof installation, windows, exterior sheathing, electrical, plumbing, HVAC, and insulation. All rough-in inspections are completed. |
| Interior Finish and Final Inspection | 4–6 weeks | Drywall, paint, flooring, kitchen, bathroom, fixtures, and all finish details. Final inspections and certificate of occupancy. |
Typical range: $80,000 – $300,000+
Most projects: $120,000–$200,000
The final cost of your adu builder in Garden City depends on several factors. Here are the biggest cost drivers:
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.
Problem: Need rental income but do not want to move
Solution: A detached ADU on your property generates $800-1,500+ monthly rental income while you continue living in your primary home.
Problem: Aging parents need close but independent living space
Solution: An ADU with a separate entrance provides privacy and independence while keeping family close. Accessibility features can be built in from the start.
Problem: Existing garage is unused and taking up valuable space
Solution: A garage conversion ADU transforms underutilized space into a functional living unit at a lower cost than new construction.
Problem: Need a dedicated workspace separate from the main home
Solution: A detached ADU configured as a studio or office provides the separation remote workers need, with the commute of a backyard walk.
Problem: Want to maximize property value and investment potential
Solution: A well-built ADU adds $100,000+ to property value and generates ongoing rental income — one of the highest-ROI improvements a homeowner can make.
Garden City shares Boise's climate. River-adjacent properties may have slightly higher humidity near the waterway.
River Proximity
Properties near the Boise River may have higher moisture levels affecting foundations and exterior materials.
Urban Heat
Being surrounded by Boise means slightly warmer summer temperatures in developed areas.
Live-Work-Create District / River Area
An eclectic area near the Boise River with a mix of residential, commercial, and mixed-use properties. Renovations here often have a creative, adaptive-reuse quality.
Common projects in Live-Work-Create District / River Area:
- •Creative kitchen remodels in compact spaces
- •Bathroom remodels maximizing small footprints
- •ADU and cottage construction on smaller lots
- •Live-work space conversions and renovations
Permit authority: City of Garden City Building Department
- ✓Permits required for plumbing, electrical, and structural work
- ✓Flexible zoning may allow more creative project types
- ✓ADU regulations support the city's compact development character
- ✓Smaller building department — personal service but may have slightly longer processing
- ●Lot placement — ADU location affects privacy, natural light, utility run distances, and neighbor sight lines
- ●Ceiling height — code minimums apply, but taller ceilings (9 ft) make a small ADU feel significantly larger
- ●Storage planning — ADUs need creative storage: wall-mounted shelving, loft storage, and built-in solutions
- ●Outdoor space — a small patio, porch, or deck at the ADU entrance adds livability and curb appeal
- ●Parking — most jurisdictions require at least one off-street parking space for an ADU
- ●Rental readiness — if the ADU may be rented, plan for durable finishes, separate utility metering, and tenant-friendly design
Here are the design trends we see most often in Garden City adu builder projects:
- →Space-efficient design maximizing compact floor plans
- →Modern and contemporary aesthetics
- →Creative material choices reflecting Garden City's eclectic character
- →Multi-function rooms and flexible spaces
- →Indoor-outdoor living connections near the Greenbelt
Garden 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.
✓Licensed general contractor with ADU-specific experience in Idaho
✓In-depth knowledge of local ADU zoning rules across Boise-area jurisdictions
✓Full architectural design and engineering included
✓Complete permitting management from application through certificate of occupancy
✓All trades licensed and insured — foundation, framing, electrical, plumbing, HVAC
✓Post-construction warranty on workmanship and installation
Do ADUs require permits and planning approval?
Yes. ADU projects require building permits, plan review, and multiple inspections. In most Boise-area jurisdictions, ADUs also require zoning compliance review to confirm lot size, setbacks, and parking requirements are met. We handle the entire permitting process.
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 long does it take to build an ADU?
From start of design to move-in, a typical ADU project takes 6 to 12 months. This includes design (4-8 weeks), permitting (4-8 weeks), and construction (3-5 months). Garage conversions are faster; detached new construction takes longer.
Can I rent out my ADU?
In most Boise-area jurisdictions, yes. ADUs can be rented as long-term rentals. Short-term rental rules (Airbnb, VRBO) vary by city and may have additional restrictions. Check local regulations before planning a short-term rental strategy.
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.
What is the maximum size for an ADU?
Maximum ADU size varies by jurisdiction. In Boise, detached ADUs can be up to 1,000 square feet or 10% of the lot area, whichever is less. Other cities in the Treasure Valley have different size limits. We confirm the specific rules for your property during the feasibility phase.
Do I need to live on the property to have an ADU?
Owner-occupancy requirements vary by jurisdiction. Some cities require the property owner to live in either the primary home or the ADU. Others have relaxed or eliminated owner-occupancy requirements. We confirm the rules for your specific location.
Will an ADU increase my property value?
Yes. A permitted, well-constructed ADU typically adds $100,000-200,000+ to property value in the Boise area — often more than the construction cost. ADUs also make a property more attractive to buyers who value rental income potential or multigenerational living flexibility.
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