Basement Apartments and Secondary Suites in Oakville, Burlington, Mississauga and Milton: What’s Allowed

Few home projects have changed as much in recent years as the basement apartment. It used to be a grey area. Today, Ontario allows one on most residential lots. Homeowners in Oakville, Burlington, Mississauga and Milton now add suites to help with the mortgage. Others want space for aging parents or adult children. Some simply want to add long-term value to their home. Buyers have noticed too, and many now search for homes with a legal suite or room to add one. Here is a plain-language guide to what’s allowed and whether a suite makes sense for you.

What Counts as a Secondary Suite?

A secondary suite is a self-contained home on the same property as the main house. Most city rules now call it an additional residential unit, or ARU. Oakville uses the term additional dwelling unit. Whatever the name, the unit has its own kitchen, bathroom and sleeping area.

In our area, the most common type is the basement apartment. You can also create an in-law suite on another floor or convert a garage. A third option is a detached backyard unit, such as a coach house or garden suite.

The key word is self-contained. A finished basement with a bedroom and a bathroom is not a legal suite. To qualify, the unit must meet local zoning rules, the Ontario Building Code and the Ontario Fire Code. In practice, that usually means:

• Proper fire separation between units
• Safe exits and windows of the right size
• Working smoke and carbon monoxide alarms
• Enough ceiling height
• Electrical and plumbing work that an inspector has approved

What Ontario Now Allows

In 2022, the province updated the Planning Act through the More Homes Built Faster Act. The change allows up to three homes on most urban lots with city water and sewer. That usually means the main house plus two more units. Both can sit inside the house, or one can go in a separate building on the lot. The rule covers detached homes, semi-detached homes and townhouses.

Each city still sets its own details, such as size limits, setbacks and parking. Several West GTA cities also go further than the provincial minimum.

The Rules in Oakville, Burlington, Mississauga and Milton

Oakville

Oakville updated its zoning in 2024. The town now permits up to four units on a detached lot. You could have the main home plus three units inside. Or you could have two units inside and one in an accessory building. Adding up to two units is generally exempt from development charges. Heritage homes may need a heritage permit before the building permit, which matters in Old Oakville. The Town of Oakville’s residential renovation page lists the permit steps.

Burlington

Burlington allows up to three ARUs on top of the main home on urban lots. Only one of those can go in an accessory building. The city actively supports ARUs as part of its housing plan. It has also waived fees on eligible new ARU permits through the end of 2026. Thinking about a suite in Burlington? Check the City of Burlington’s ARU page soon to see if the waiver still applies.

Mississauga

Mississauga allows the main home plus up to two ARUs, or a fourplex on the lot. The city says homeowners can build a detached ARU on more than 130,000 lots. Its Building More Units page explains your options, the permit process and typical wait times.

Milton

Milton allows up to three ARUs, for four homes in total on most urban lots. That covers detached, semi-detached, semi-link and townhouse properties. Milton also asks owners to register every ARU, new or existing. The town inspects the unit and charges a one-time fee of $340 per unit. Owners then renew each year. The Town of Milton’s ARU page has the details.

These rules keep changing. Before you start a design, confirm the current requirements with your city’s building department.

Why “Legal” Matters

Skipping permits can feel tempting, especially if your basement is already partly finished. But an unpermitted suite puts you at risk, both now and when you sell.

Your home insurance may not cover an illegal unit if something goes wrong. The unit can also put the people living in it in danger. And when you sell, buyers and their lenders will ask about permits and final inspections.

A legal suite can be a real selling feature. An unpermitted one often hands the buyer a reason to negotiate your price down. Some lenders also won’t let buyers count rental income from a suite that isn’t legal.

Financing a Secondary Suite

A suite is a big project, but you now have more ways to pay for it. Since January 2025, a federal insured refinance option has helped homeowners fund new suites. You can borrow up to 90 per cent of your home’s value, including the value the suite adds. The property value limit is $2 million, and you can spread payments over up to 30 years.

There are a few conditions. You can’t use the new unit as a short-term rental. Not every lender offers the program either, so talk to a mortgage professional early.

A new unit can also raise your home’s assessed value and your property taxes. Rental income affects your taxes as well. A quick chat with your accountant before you build can help you plan.

How a Suite Affects Your Home’s Value

A well-built legal suite can widen your pool of buyers when you sell. Multigenerational families want one. So do buyers who need help with mortgage payments, and small investors. Rental demand tends to run highest near transit, colleges and job hubs. Think of homes near Sheridan College in Oakville or close to a GO station. Our guide to living near the GO train in Oakville, Burlington, Mississauga and Milton shows which neighbourhoods have the best transit access.

Still, a suite doesn’t suit every home. Ceiling height, a separate entrance, parking and lot size all affect what’s practical. In some of our premium neighbourhoods, buyers may value a family basement as much as a rental unit.

Thinking About Buying a Home With a Suite?

Shopping for a home with a basement apartment? Start by asking the seller for permit and inspection records. Next, confirm the unit is registered if your city requires it. Your home inspector should also look closely at fire separations, exits and the electrical panel.

If a tenant lives in the unit, read the lease before you firm up your offer. Make sure you understand your duties as a landlord under Ontario’s tenancy rules. Our guide to finding the right West GTA neighbourhood for your life stage can also help you decide if a home with a suite fits your plans.

Let’s Talk About Your Property’s Potential

Maybe you want a basement apartment to help with the mortgage. Maybe you need space for family, or you’re shopping for a home that already has a legal suite. Either way, the David Bradica Team can explain what it means for value and resale in your neighbourhood. We work with homeowners across Oakville, Burlington, Mississauga and Milton every day. Reach out to our team anytime for a no-pressure conversation.