How much does it cost to build an ADU in Virginia?

There is no single Virginia price. The Virginia Housing Commission, in its introductory brief on ADUs, says the cost depends on factors like square footage and whether an ADU is attached or detached.^[1] Your real number comes from itemized written quotes after a builder has seen your lot and your house.

What moves the price

Attached or detached. The brief says constructing an attached ADU, like converting a garage, typically costs less than a detached ADU.^[1] A garage or basement already has a floor, walls and a roof. A backyard cottage needs a foundation, a full structure and a roof of its own.

Size and finish. A studio is cheaper than a two-bedroom, and a full kitchen and bath cost far more per square foot than bedrooms do. Quality of finishes moves the total as much as the footprint.

Utilities. A separate unit needs water, drain, electric and heating and cooling. Running lines to a detached building across the yard can mean trenching, a new electrical subpanel and a larger water service. If the house is on a well or septic system, additional documentation may be required by the Health Department to accommodate any additional bedrooms,^[3] and a septic upgrade can be a big separate line item.

Site work. Slope, drainage, trees, access for equipment and soil all affect foundation and grading costs. Ask the contractor what is assumed.

Local requirements. Localities may also require replacement of the main house's required parking and dedicated parking for the ADU.^[2] They may require compliance with water, sewer, septic, emergency access, flood zone and stormwater requirements.^[2] Each can add paving, drainage or engineering to the bill.

Fees to budget separately

Under the state ADU law, effective July 1, 2027, a locality may charge a fee of no more than $500 for the ADU permit, in addition to any inspection, site or building permit fees.^[2] Building permit fees are set by each locality, so ask yours for its schedule.

As of October 2026, Fairfax County, which has its own accessory living unit rules, lists its accessory living unit application fee at $285 and a renewal at $75.^[3]

Design and engineering drawings, surveys, utility connection charges and the cost of financing are usually outside a contractor's construction price, so ask what is left out.

Costs after it is built

Insurance deserves a call before you commit. The commission's brief says those renting out a detached unit to a non-family member may be required to purchase landlord insurance, which can add to the budget.^[1] Property taxes, utilities and the zoning rules on renting also affect what the unit really costs you; see whether ADUs are allowed in Virginia.

Getting quotes you can compare

Ask each builder to price the same scope in writing, showing:

• design and drawings, and who handles permits
• foundation, framing, roof, windows and exterior finish
• plumbing, electrical and heating and cooling, with separate lines for any new service or subpanel
• kitchen and bath allowances, with the brand and grade assumed
• site work, utility trenching, septic or sewer work and landscaping repair
• the payment schedule, schedule and warranty

Compare the scope, not just the total. The cheapest quote is often the one that leaves out utilities or site work. Read what building an in-law suite involves so you know what a complete quote covers.

When to call a licensed pro

For the whole job. Virginia's contractor licence classes turn on contract value: Class C for a single contract over $1,000 but less than $30,000, Class B for $30,000 or more but less than $150,000, and Class A for $150,000 or more.^[4] A whole ADU will usually land in Class B or Class A. Check the licence on DPOR's lookup before you pay a deposit.

Browse remodeling services or read more remodeling answers. To get prices for your own lot, describe the job once and licensed local remodelers quote it.