ADU rules in McKinney

Detached ADUs (the UDC also calls them backyard cottages) are allowed by right as an accessory use in all seven single-family districts (R43, R12, R8, R6, R5, R3, TR1.8) plus AG, shown as 'A' in Table 2-26 with no Specific Use Permit. Only one ADU is allowed per conforming lot, and it must sit behind the front face of the house with the same setbacks and height limit as the main dwelling. Small-lot single-family lots are excluded, and multifamily, commercial, and industrial districts do not allow ADUs at all.

McKinney's UDC defines an accessory dwelling unit as detached from the primary dwelling; there is no attached-ADU pathway. Anything attached to the house is treated as an extension of the primary building, and a second full dwelling unit under the same roof would be a duplex, a separate use not allowed in single-family districts. An attached in-law suite can exist only as ordinary interior space of the home, not as a separately regulated dwelling unit. The Regional Employment Center appendix separately allows rear-yard garage apartments in that special district.

The cap scales with the house: a 1,600 sq ft home allows an ADU up to 800 sq ft, while an 1,100 sq ft home allows up to 825 sq ft under the 75 percent small-home allowance. There is no separate fixed square-footage ceiling in the ordinance. The city guidebook notes a one-story home means a one-story ADU.

Nothing in the ADU standards requires the owner to live in either unit; a full-text search of the UDC found an owner-occupancy requirement only for bed and breakfasts. What the code does require is unified ownership: the ADU must stay under the same ownership as the primary dwelling, cannot be sold off separately, and cannot have its own electric meter. Both units can therefore be rented while the owner lives elsewhere.

Because a standard McKinney single-family home must already provide 4 spaces (2 in a garage), most lots will not owe any additional space for the ADU; 1 space is added only if the lot is below the threshold. The city's ADU guidebook restates this as: 4 or more existing spaces means no extra spot, fewer than 4 means add 1.

ADUs are marked 'A' (accessory use) in Table 2-26 for the eligible districts, not 'S' (Specific Use Permit), so no discretionary zoning approval is needed; the owner applies for a standard building permit through the Citizen Self-Service portal and must meet the §205G.2.b standards. In the H Historic Overlay a Certificate of Appropriateness must be approved before any permit for a new ADU. Planned Development districts follow their own ordinances and may not allow ADUs.

The UDC places no restriction on renting an ADU long term. For short-term rental, McKinney now requires each dwelling unit to be registered annually (no fee) with a designated 24-hour responsible person; operating an unregistered STR is an offense. The registration program does not cap STRs or impose owner occupancy, but HOA covenants and deed restrictions still apply and the city program expressly does not supersede them.