Lewisville, TX Accessory Structures: ADU Rules (2026)

Lewisville permits accessory dwelling units in residential zoning districts subject to the Unified Development Code requirements. ADUs may be attached to or detached from the primary dwelling but must remain subordinate in size, typically limited to no more than 800 square feet or a percentage of the primary dwelling's floor area, whichever is less. The ADU must comply with all applicable building codes including the International Residential Code as adopted by the city. Detached ADUs must meet the same setback requirements as other accessory structures, typically 5 feet from side and rear property lines. Only one ADU is permitted per lot. The property must maintain required parking for both the primary dwelling and the ADU. ADUs cannot be subdivided or sold separately from the primary residence. A building permit is required and site plan review may be needed depending on the zoning district. The ADU must connect to city water and sewer services. Septic systems are not permitted for ADUs within city limits. Construction must meet current energy code requirements. Contact Lewisville Planning at (972) 219-3600 for zoning verification and the Inspections Division at (972) 219-3480 for permits.