Can you add a basement apartment in Sherbrooke?

The rules, in short

• An integrated additional dwelling unit is allowed in a detached single-family house inside the urban perimeter, within the house or an extension; one of the units must be the principal residence of the owner or an occupant. (art. 5.3.12, 1) to 3))
• It may occupy every level, basement included, up to 35% of the total floor area (basement included, garage excluded). (art. 5.3.12, 8))
• Only one door on the main façade; the additional unit's door goes on the sides or at the rear (side balcony of 5 m² max.); a separate civic number; a single water and sewer connection. (art. 5.3.12, 4) to 7))
• Complementary (intergenerational) unit: detached single-family house, at most 2 bedrooms and 35% of the floor area, an inside connection that must not be lockable, a single door on the façade, not entirely in the basement unless one side or the rear is fully above grade. (art. 5.3.10)
• Detached additional unit (in a separate building): possible with a detached single-family or two-family house, on a serviced lot of at least 450 m², at most 70 m² of floor area, after council approval (conditional use). (art. 5.3.13)

Summary by Radar Foncier, in our own words: the official French text of the by-law, linked above, prevails.

Applying in Sherbrooke

• Processing time: Permit issued in 30 minutes at an in-person appointment if the documents are complete (pool, accessory building); no processing time published for other methods
• Cost: Accessory building (residential): $76.25 for $0 to $5,000 of work, plus $2.50 per additional $1,000; other permits and certificates under By-law 1202
• Urban planning department: Borough inspectors' offices (e.g. Des Nations borough, 731 Galt Street West, suite 200: 819 821-5905)
• Permits on the municipality's website