Accessory Dwelling Unit (ADU) Construction Cost
ADUs (granny flats, in-law suites) are one of the highest ROI investments due to rental income potential. Many cities have streamlined ADU permitting to address housing shortages.
Low Estimate
$60,000
Mid-Range
$150,000
High End
$350,000
Avg ROI
80%
Interactive Cost Estimator
Mid-grade materials, good quality fixtures, standard options.
Estimated Total Cost
$150,000
Based on 200 sq ft at mid quality. Actual costs vary by location and contractor.
Accessory Dwelling Unit (ADU) Construction Quote Sanity Check
Use this range before signing a contractor proposal. A normal written bid for accessory dwelling unit (adu) construction should explain labor, materials, permits, cleanup, timeline, exclusions, and change-order pricing.
Question a low bid
Below $54,000
Ask what is excluded, whether materials are allowances, and whether permits, disposal, and finish work are included.
Expected planning range
$60,000 - $350,000
The midpoint is $150,000, before optional upgrades and unexpected conditions.
Require line-item detail
Above $385,000
Premium bids can be valid, but they should name brands, quantities, warranty length, project management, and finish level.
Labor budget
$75,000
50% of midpoint
Materials budget
$75,000
50% of midpoint
Contingency
$15,000 - $30,000
10-20% buffer
Decision rule
3 comparable bids
Same scope, same finish level
Cost Breakdown
Approx. $75,000 at mid-range pricing
Approx. $75,000 at mid-range pricing
Labor-heavy projects (with high labor costs) benefit most from getting multiple contractor bids. You can save on materials-heavy projects by sourcing materials yourself at contractor pricing.
Contractor Quote Worksheet for Accessory Dwelling Unit (ADU) Construction
Use this checklist when comparing bids. The cheapest quote is not always the lowest final cost; the bid that defines scope, allowances, permits, cleanup, and change-order rules usually gives the cleaner budget.
| Bid line | What to ask | Why it matters |
|---|---|---|
| Scope definition | Confirm what is included in the accessory dwelling unit (adu) construction base bid and what is priced as an allowance or option. | Vague scope turns into change orders after demolition or material selection. |
| Labor assumptions | Labor is about 50% of the mid-range budget. Ask whether demo, prep, cleanup, disposal, and final punch-list time are included. | A low bid may exclude prep work, disposal, or return trips. |
| Material allowances | Materials are about 50% of the budget. Get brand, grade, finish, and quantity assumptions in writing. | Allowance bids look cheap until fixtures, finishes, or delivery fees are upgraded. |
| Permit and inspection plan | Confirm who pulls permits, who pays fees, and when inspections happen. | Permit gaps can delay final payment, insurance claims, or home resale. |
| Timeline and disruption | The normal timeline is 6-18 months. Ask what happens if materials arrive late or hidden conditions are discovered. | A fast verbal timeline without milestones is hard to enforce. |
Normal range
$60,000 - $350,000
Contingency
$15,000 - $30,000
Quote target
3 bids minimum
ADU Zoning, Utility, and Independent-Living Audit
ADU construction is a small home build, not a bedroom addition. A credible bid should separate zoning feasibility, independent kitchen and bath scope, utility tie-ins, fire separation, privacy, parking, and the inspection sequence before pricing finishes.
Scope checks
- 1Confirm whether the unit is detached, attached, garage conversion, basement, or internal space, and verify setbacks, size limits, owner-occupancy rules, parking rules, rental license rules, and local design standards.
- 2Ask how the price handles separate sleeping area, full bath, kitchen, water heater, HVAC, electrical panel capacity, sewer or septic capacity, utility metering, fire separation, egress, and sound control.
- 3Define the permit path, survey or site plan, foundation or slab scope, trenching, drainage, accessibility goals, privacy screening, address assignment, and final certificate of occupancy before selecting finishes.
Quote traps
- A detached ADU price that excludes utility trenching, sewer capacity, electrical service upgrades, drainage, driveway or walkway work, or impact fees.
- A garage or basement conversion quote that ignores legal ceiling height, emergency escape openings, fire separation, moisture, ventilation, or rental licensing.
- Assuming local ADU rules are automatic; many cities still require plan review, inspections, design standards, or separate occupancy paperwork.
Proof to collect
- ✓Zoning confirmation, permit plan, site plan, and inspection schedule before deposit.
- ✓Utility load notes, panel capacity, sewer or septic confirmation, HVAC sizing, and water-heater approach in writing.
- ✓Rough-in photos before closure for framing, fire separation, insulation, air sealing, plumbing, electrical, and mechanical systems.
Reference sources
What Affects the Price
- 1Attached vs detached
- 2Size and bedroom count
- 3Kitchen and bath quality
- 4Local ADU regulations
- 5Utility connections
Popular Upgrades
- Full kitchen
- Separate entrance
- Solar panels for energy independence
Discuss upgrades with your contractor before finalizing the quote. Some upgrades are cheaper to include during initial construction than to add later.
DIY vs. Hire a Pro
Professional installation strongly recommended.
DIY Advantages
- • Save 50% on labor costs ($75,000 at mid-range)
- • Control over timeline and material selection
- • Satisfaction of completing the project yourself
- • Flexibility to work in phases
Pro Advantages
- • Guaranteed workmanship and professional finish
- • Proper permits and code compliance
- • Access to trade pricing on materials
- • Required for safety and code compliance
Local Accessory Dwelling Unit (ADU) Construction Cost Examples
Related Additions & Structures Projects
Explore All 120 Project Cost Guides
Compare costs across every major home improvement category — kitchens, baths, roofing, flooring, HVAC, additions, and landscaping.
View All Project Costs