Cost to Build a Basement Apartment in Ontario (2026)

Building a basement apartment in Ontario is a significant investment that can yield excellent returns. The cost to build a basement apartment in Ontario varies depending on the current state of your basement, required permits, and chosen finishes. Typically, homeowners can expect to spend between $60,000 and $100,000 for a fully legal, code-compliant secondary suite. Factors such as underpinning, egress window installation, and separate HVAC systems play a major role in the final price. Contact Ground Level Construction for an accurate quote tailored to your property, or explore our basement apartment construction in Cornwall services to learn more.