Quick Answer: Calgary flat roofing covers low-slope roof systems used on modern homes, garages, additions, dormers, and most commercial buildings. Common materials include SBS modified bitumen, TPO, EPDM, and built-up systems, each priced from $8 to $20 per square foot installed. Drainage, snow load capacity, and Chinook freeze-thaw resistance matter more than aesthetics. Properly installed flat roofs last 20 to 30 years in Calgary's climate with documented annual maintenance