Detached ADU in Markham - Design, Permits, Construction

Unionville and Markham Village sit inside designated heritage conservation districts, so a rear-yard garden suite there needs Heritage Permit approval on top of the building permit - cladding, roof pitch and window proportion all get reviewed. Cornell and Wismer lots two concessions away have no such requirement. Markham permits additional dwelling units city-wide, but heritage designations in Unionville and Markham Village add a Heritage Section 42 review to rear-yard construction.

Mixed - heritage-district lots with strict design review, alongside large 1990s subdivision lots in Cathedraltown and Wismer with ample rear yards. Markham sees 137 cm of snow and -4.5°C winter averages. Ontario's 1.2 m frost-depth requirement governs every footing we pour for detached adu, and the April-November season sets the excavation window.

A detached unit stands clear of the main house, so it carries its own foundation, its own service laterals and its own exit - the three cost centres that separate it from an interior conversion on the same Markham lot. We trench services across the yard and pour to 1.2 m before the ground closes; framing, envelope and interior finishing then run through the cold months without holding up occupancy. Detached is the highest per-square-foot form of the four, and also the only one that leaves the existing house untouched - no shared walls, no disruption to the occupants during construction.