What Virginia ADUs actually cost.
Written to be useful before you talk to any builder. We'll be honest even when it costs us the project.
Written by Dan Caporale, Principal, Hearthstone Design Build
Interior ADU conversions in Virginia typically run $60,000–$150,000. New detached backyard cottages typically run $180,000–$400,000+, or about $180–$400+ per finished square foot depending on site conditions, utility runs, finish level, and county.
Virginia ADU cost key facts
- Interior conversion
- $60,000 – $150,000
- New detached cottage
- $180,000 – $400,000+
- Per square foot
- $250 – $400 finished
- Design, engineering & permits
- 8 – 12% of project cost
- Typical NoVA rent
- $1,500 – $2,500+ per month
- SB 531 permit-fee cap
- $500, effective July 1, 2027
What drives the range
- • Utility runs — water, sewer, gas and electric distance from the main house.
- • Sewer vs septic — septic capacity can require an entire drainfield upgrade.
- • Site conditions — slope, drainage, trees, rock, access for equipment.
- • Foundation type — slab vs crawlspace vs full basement.
- • Envelope — cladding, roof, windows.
- • Finish level — cabinets, flooring, appliance package, tile selections.
Rough cost split, new detached ADU
Rent side of the equation
Northern Virginia rents for a well-designed detached ADU typically land $1,500–$2,500+/month. That doesn't include short-term-rental premiums where allowed. Even at conservative long-term rent, a $250k build in a strong rental submarket often reaches meaningful cash-on-cash returns once stabilized. Weighing this against expanding the main house? Read ADU vs. home addition. Working with an existing garage instead? See garage conversion ADUs in Virginia, or compare it head-to-head with a new cottage in garage conversion vs. new detached ADU. Weighing a factory-built unit against building on site? Read prefab vs. site-built ADUs.
Frequently asked
How much does a Virginia ADU cost in 2026–2027?+
Interior ADU conversions in Virginia typically run $60,000–$150,000. New detached backyard cottages typically run $180,000–$400,000+, or roughly $180–$400+ per finished square foot.
What drives ADU cost the most?+
Utility distance from the main house, sewer vs septic capacity, site conditions (slope, trees, access), foundation type, envelope choices, and interior finish level are the biggest drivers.
How much rent can a Virginia ADU earn?+
A well-designed detached ADU in Northern Virginia typically rents for $1,500–$2,500+ per month long-term. Short-term rental premiums apply where locally allowed.