Finish Your Basement or Build a Legal Secondary Suite in Ottawa?

The short answer

A finished basement adds living space for your household: a family room, office or guest bedroom. A legal secondary suite is a separate home inside your home with its own entrance, kitchen and bathroom, and it must meet more rules. The suite costs much more and takes more approvals, but it can earn rental income.

Published costs for Ottawa

These figures come from HomeStars’ 2026 Ottawa basement renovation guide, updated in August 2026. They are published ranges for context and are not Aelia quotes. We checked them in October 2026.

• Whole basement renovation: about $35,000 to $95,000
• Most 700 to 900 square foot basements land between $50,000 and $75,000 for a mid-range finish
• Basement bathroom addition: about $15,000 to $30,000
• Legal secondary suite, mid-range one-bedroom: about $80,000 to $120,000 all-in
• Waterproofing and insulation upgrades: about $5,000 to $15,000 on either project

What a legal suite requires

HomeStars lists these requirements for an Ottawa secondary suite. Treat them as a starting point, because rules change, and confirm the current requirements with the City of Ottawa.

• A zoning that allows a second unit on the property
• Minimum unit sizes: HomeStars cites 28 square metres for a bachelor and 37 for a one-bedroom
• Fire separation between the units, which HomeStars cites as 45 minutes
• A separate entrance
• A full kitchen and at least one bathroom
• Code-compliant egress windows in all bedrooms
• An independent heating source
• Electrical panel upgrades and a separate circuit

Permits and drawings

The City of Ottawa requires a building permit to finish a basement. A secondary suite involves more review than a basement for your own use, and professional drawings are part of the cost. See our guide on whether you need a permit to finish a basement.

Return on investment

HomeStars estimates Ottawa homeowners recover about 60 to 75% of basement renovation costs at resale, with a finished basement adding roughly 15 to 25% to a home’s market value. It says a legal suite tends to exceed that return where rental demand is strong. These are general estimates, not guarantees.

How to decide

• Choose a finished basement if you want more space for your family and a smaller budget.
• Consider a legal suite if you want rental income or a separate space for a relative, and you can fund the higher cost and the approvals.
• Whichever you choose, fix moisture and foundation problems first.
• Ask the City whether your property qualifies before you spend on drawings.

Plan your basement

Aelia Construction and Design offers free estimates for basement finishing across Ottawa, Kanata, Barrhaven, Nepean and Orleans. We can explain what each option would involve for your home.