ADU rules in Delaware
Representative cities: Wilmington, Dover.
ADU permit rule
Permit requiredCase by casecounty authority
Fee basis
Valuation-based; set by the county (unincorporated) or city.
Typical timeline
Varies
Setback
—
Area threshold
Not size-exempt
Exempt if
None — an ADU always requires a building permit where local zoning allows it.
Go / no-go
case-by-case
Delaware has no statewide building/residential code — codes are adopted at the county and municipal level. ADUs are allowed only where the local zoning ordinance permits them (Wilmington and the counties vary). When permitted by zoning, a full building permit is required.
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Frequently asked questions
Do I need a permit to build an ADU in Delaware?
Per Delaware rules, an ADU is "yes" for a permit and the authority is "county". Delaware has no statewide building/residential code — codes are adopted at the county and municipal level. ADUs are allowed only where the local zoning ordinance permits them (Wilmington and the counties vary). When permitted by zoning, a full building permit is required. Always confirm with the issuing building department.
How big can an ADU be in Delaware?
Size limits for an ADU in Delaware are set by local zoning — verify with your city building department.
What are the ADU setbacks in Delaware?
Setback rules vary by city in Delaware; confirm with the local planning or building department.
How much does an ADU permit cost in Delaware?
Fee basis: Valuation-based; set by the county (unincorporated) or city.