ADU Construction Costs by State & City
Verified construction cost benchmarks, permit fee ranges, and rental ROI data across California, Texas, Florida, Washington, Oregon, Arizona, and Colorado. Use our interactive estimator to calculate your exact project budget.
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Avg Construction Cost
$250 – $350/sq ft
Permit Drawings Cost
$6,000 flat
Drawings Turnaround
10 Days business
Avg 1BR Monthly Rent
$1,200 – $2,100/mo
Interactive ADU Cost Estimator
Select your location, building type, size, and finish quality to generate a localized construction breakdown, permit fee estimate, and projected monthly rental income.
Estimated Investment
Estimated Construction Build Cost
$203,274
$338 / sq ft effective rate
ADU Costs & Rental Returns Across 7 Core States
Data compiled directly from city building departments, permit portal fee schedules, and regional rental market analysis in our compliance database.
| State | Tracked Cities | Avg Cost / Sq Ft | Permit Fee Range | Plan Check Time | Median 1BR Rent | Median 2BR Rent | Explore Cities |
|---|---|---|---|---|---|---|---|
| CA California | 185 cities | $338.79 / sq ft | $1,447 – $92,772 | 9 wks | $2,050.08/mo | $2,581.84/mo | California ADUs → |
| TX Texas | 115 cities | $254.67 / sq ft | $95 – $31,364 | 5.5 wks | $1,161.45/mo | $1,482.9/mo | Texas ADUs → |
| FL Florida | 106 cities | $261.71 / sq ft | $302 – $48,695 | 6.6 wks | $1,644.59/mo | $2,120.42/mo | Florida ADUs → |
| WA Washington | 65 cities | $325.41 / sq ft | $700 – $33,749 | 8.3 wks | $1,633.83/mo | $2,009.69/mo | Washington ADUs → |
| OR Oregon | 50 cities | $285.44 / sq ft | $101 – $65,050 | 7 wks | $1,375.4/mo | $1,581.1/mo | Oregon ADUs → |
| AZ Arizona | 48 cities | $264.22 / sq ft | $487 – $25,000 | 6.5 wks | $1,239.23/mo | $1,592.17/mo | Arizona ADUs → |
| CO Colorado | 48 cities | $297.5 / sq ft | $491 – $60,339 | 7.7 wks | $1,587.3/mo | $1,888.57/mo | Colorado ADUs → |
ADU Costs by Construction Method
Your choice of building type dictates 50%+ of your overall cost structure. Here is how the five primary ADU construction methods compare on cost, framing demands, and rental performance.
Detached ADU
$280–$450/sq ftStandalone building with 4 new exterior walls, dedicated foundation, and independent utility connections.
- ✓ Maximum tenant privacy & zero shared walls
- ✓ 10%–20% rental income premium
- • Requires side & rear setback clearance (4–8 ft)
Attached ADU
$220–$350/sq ftHome addition sharing at least one wall with the primary residence. Often steps off existing footings.
- ✓ Lower foundation & exterior envelope cost
- ✓ Shorter utility trenching runs
- • Requires 1-hour fire-rated separation wall
Garage Conversion
$120–$220/sq ftTransforms an existing detached or attached garage into a self-contained living space.
- ✓ Lowest cost per square foot
- ✓ Utilizes existing slab & framing shell
- • May require slab infill or roof insulation upgrade
Junior ADU (JADU)
$80–$150/sq ftConverted space (bedroom, attic, master suite) entirely within primary house footprint under 500 sq ft.
- ✓ Minimal structural framing required
- ✓ Requires efficiency kitchen & exterior entrance
- • May require owner-occupancy depending on state
2-Story / Above-Garage
$320–$500/sq ftSecond-story ADU constructed over a garage or as a two-level detached floor plan.
- ✓ Preserves yard space & ground lot area
- ✓ Premium views & privacy
- • Requires structural beam retrofits & stairwell
Backyard Wealth Package
Full architectural plan set (site plan, floor plans, elevations, sections, structural notes, Title 24/energy) ready for city submittal.
$6,000 flat
Guaranteed 10 business days turnaround
Popular City ADU Cost Pages
City-specific permit office requirements, local setback rules, and localized contractor cost averages:
Featured ADU Floor Plan Designs
Explore permit-ready layout options optimized for maximum living efficiency and rental appeal:
ADU Cost & Investment FAQs
How much does an ADU cost per square foot in 2026?
On average across our 7 target states, ADU construction costs range from $220 to $450 per square foot for new detached construction, $180 to $350 for attached additions, and $120 to $220 for garage conversions. California and Washington rank highest ($320–$350+/sq ft), while Texas and Florida average $250–$265/sq ft.
What is the cheapest type of ADU to build?
Garage conversions and Junior ADUs (JADUs) are the most cost-effective options, typically costing between $40,000 and $150,000 total. Because they utilize an existing concrete slab and building envelope, you eliminate 30–40% of standard framing and foundation costs.
How much do ADU building permits cost?
Building permit fees vary significantly by city and square footage. In smaller municipalities or for units under 750 sq ft (where impact fees are waived by law in states like California), permit fees range from $1,000 to $4,500. For larger standalone units in high-fee cities, total permit and impact fees can reach $15,000 to $50,000.
How much do architectural drawings and design cost for an ADU?
Traditional architects typically charge 8% to 15% of total construction cost — often $15,000 to $35,000 just to start design. Build With A Plan delivers full permit-ready architectural drawing sets for a flat $6,000 Backyard Wealth Package (or $997–$2,997 self-serve packages) in strictly 10 business days.
What hidden costs catch ADU builders off guard?
The top hidden ADU costs include: utility trenching (water/sewer lines run $50–$150/linear foot), main electrical panel upgrades (adding $2,500–$6,000), separate utility meters ($2,000–$8,000), Title 24 / energy compliance calculations ($500–$1,500), and site grading/soil drainage modifications.
Does an ADU increase property taxes and home equity?
Yes. An ADU triggers a blended property tax reassessment on the added square footage only — your primary home rate remains unchanged under state protections like Prop 13 in CA. In high-demand markets, a completed ADU typically increases total property appraisal by 100% to 150% of the construction cost.
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