ADU Cost Calculator
Calculate building costs for detached backyard homes, granny flats, attached suites, and garage ADU conversions. Estimate materials, trade labor rates, demolition fees, municipal permits, waste margins, and contingency reserves with regional state multipliers.
ADU Cost Calculator
Interactive cost model calculating project size, materials, labor, demolition, permits, waste margin, and contingency reserves.
Project Specifications
Estimated Project Budget
MID-RANGE SPECItemized Budget Allocation
Important Planning Notice: These figures are planning estimates for budgeting and preliminary feasibility. Actual project costs depend on specific municipal code requirements, substrate conditions, structural access, material selections, and formal contractor bidding.
Key Cost Drivers & Estimation Factors
Understanding where your project dollars go is essential for accurate bidding and budget control.
Utility Lateral Connections (The Hidden Cost)
Trenching 50–100 feet to connect sewer, water, and electrical to the main street or house costs $10,000–$25,000.
Municipal Permitting & Impact Fees
Depending on your municipality, city impact and school fees range from $2,500 to over $18,000 for detached ADUs.
Foundation & Site Topography
Sloped yards requiring retaining walls or engineered grade beams add $12,000–$30,000 in groundwork.
Separate Metering vs. Sub-metering
Installing a separate utility electric meter for tenant billing adds $3,500–$6,500 in utility company connection costs.
Itemized Scope & Quality Tier Comparison
Compare material grades, structural scopes, and labor costs across budget, mid-range, and luxury tiers.
| Scope Component | Budget / Economy | Mid-Range (Standard) | High-End / Custom | Trade Notes |
|---|---|---|---|---|
| Site Prep, Trenching & Foundation | $12,000–$20,000 | $25,000–$42,000 | $45,000–$75,000 | Slab-on-grade with underground plumbing runs |
| Framing, Windows, Roof & Siding | $22,000–$35,000 | $45,000–$75,000 | $80,000–$135,000 | Complete weather-tight structural building envelope |
| Plumbing, Electric (100A) & Mini-Split HVAC | $16,000–$25,000 | $30,000–$52,000 | $55,000–$85,000 | Sewer lateral, PEX water lines, heat pumps |
| Kitchenette & Full Bathroom Packages | $10,000–$18,000 | $22,000–$38,000 | $42,000–$70,000 | Cabinets, quartz tops, appliances, tile shower |
| Drywall, Interior Doors, Trim & Flooring | $9,000–$15,000 | $18,000–$32,000 | $34,000–$58,000 | Insulation R-21/R-38, paint, vinyl plank |
State-by-State Cost Adjustments
How regional contractor labor wages and local building material costs adjust typical pricing across key states.
| State | Cost Multiplier | Labor Rate Multiplier | Typical 650 sq ft Estimate | Index Variance |
|---|---|---|---|---|
| California | 1.25x | 1.30x | $231,563 | +25% above US avg |
| Texas | 0.92x | 0.90x | $170,430 | -8% below US avg |
| Florida | 0.96x | 0.94x | $177,840 | -4% below US avg |
| New York | 1.20x | 1.22x | $222,300 | +20% above US avg |
| Pennsylvania | 1.02x | 1.01x | $188,955 | +2% above US avg |
| Illinois | 1.06x | 1.08x | $196,365 | +6% above US avg |
| Ohio | 0.90x | 0.88x | $166,725 | -10% below US avg |
| Georgia | 0.93x | 0.91x | $172,283 | -7% below US avg |
| North Carolina | 0.91x | 0.89x | $168,578 | -9% below US avg |
| Michigan | 0.98x | 0.96x | $181,545 | -2% below US avg |
Pro Tips for Budgeting Your ADU Cost
Lock In Your Scope Before Demolition
Change orders during active construction cost 25% to 50% more than planning changes on paper. Finalize all plumbing fixtures, tile selections, and layout plans before swinging the first sledgehammer.
Confirm Municipal Permit Jurisdiction
Municipalities require permits for structural alterations, new electrical runs, plumbing relocations, and exterior envelope work. Unpermitted work can void homeowner's insurance claims and stall property resale.
Order Extra Material for Waste (10%)
Running out of material halts trade subcontractors. Dye lots on tile, batches of siding, and hardwood runs can differ slightly between production runs. Always order with waste included.
Preserve a 15% Liquid Contingency Reserve
Hidden surprises behind drywall or beneath subflooring are standard in remodeling. Maintaining contingency funds guarantees you complete your project without compromising on finish quality.
Frequently Asked Questions
How much does it cost to build an ADU from scratch?
Nationwide, a typical 600 sq ft detached ADU costs between $140,000 and $220,000 all-in (including site work, utility trenching, permits, and finishes). High-cost areas like California, Seattle, and New York often see $250,000 to $380,000+.
Can an ADU generate rental income?
Yes. ADUs frequently rent for $1,400 to $2,800+ per month depending on location, providing an attractive 8% to 14% capitalization rate that can cover mortgage payments or provide retirement income.