Buying a House with a Legal Basement Apartment (GTA 2027)

Published 2 November 2026 · By Jatin Dua, Broker of Record, RE/MAX Quantum Realty

What's Your Home Worth Right Now?

Get a free AI-powered price range for your property in under 90 seconds, based on recent GTA comparable sales. No name or address required.

Get My Free Estimate →

Brampton detached house with a separate side entrance to a basement unit (illustrative)

By Jatin Dua · Broker of Record, RE/MAX Quantum Realty · Updated 2 November 2026 · 9 min read — How to confirm a GTA basement apartment is legal, how much of its rent lenders count toward your mortgage, and what happens to the tenant.

Short answer

Before buying a GTA house with a basement apartment, confirm it has a building permit with final inspection and, in Brampton, Mississauga or Markham, that it is on the city’s registry. For an owner-occupied two-unit house with a CMHC-insured mortgage, CMHC allows up to 100% of the gross rent to be added to your income, which can cut the income you need by tens of thousands of dollars.

This guide is for buyers in Toronto and the GTA who want a house with a basement apartment, either to help carry the mortgage or to house family. You will learn how to prove the unit is legal before you firm up, how much of the rent a lender can count, and what happens to a tenant who is already living there.

What makes a basement apartment legal in Ontario?

A legal basement apartment is a self-contained unit, with its own kitchen, bathroom and sleeping area, that meets three sets of rules:

Zoning: the city must allow a second unit on that lot. Brampton’s zoning, for example, allows up to three units in total, including the main house. Toronto permits up to four units as of right across the city.
Building Code: the unit needs a building permit and inspections. Ontario’s guide for second units sets minimums such as a basement ceiling height of 1.95 m (6 feet 4¾ inches) over the required floor area, minimum room and window sizes, and a fire separation between the units.
Electrical and fire safety: the province says a second unit needs a separate electrical permit and an Electrical Safety Authority inspection, a 30-minute fire separation between the units (15 minutes if the whole house has interconnected smoke alarms), smoke alarms in each bedroom of the unit, and safe exits.

Some cities add a fourth step: registration. A finished basement with a kitchen is not the same as a legal unit. Without the permits and sign-offs, it is just a basement someone rents out.

How do you check if a basement apartment is legal before you buy?

Ask the seller for the building permit, the final inspection sign-off, the electrical certificate and, where the city requires it, proof of registration. Then check the city’s own records. Here is what four GTA cities say on their websites.

City	Registration rule	What you can check
Brampton	All additional residential units must be registered, including older ones once treated as legal non-conforming	Public lists of registered units and of active registration permits
Mississauga	All second units must be registered; no fee to register	Second Units Registry List, updated the second week of each month
Markham	All two-unit houses must be registered after a fire inspection	Ask the owner for the registration; fees are $260 for the first fire inspection and $246 to register
Toronto	The city’s secondary suites page refers owners to Toronto Building for permit and code rules	Building permit history and final inspections for the address

Source: City of Brampton, City of Mississauga, City of Markham and City of Toronto websites, checked November 2026. Other GTA cities have their own rules; ask the local building department.

Markham also notes that a second suite built before 1 July 1993 may be assessed under the Fire Code’s retrofit rules for two-unit houses instead of the current Building Code, if the owner can prove its age. If a listing calls a unit “legal” and the seller cannot show any of these documents, treat it as not legal until proven otherwise. My older post on buying a house with a basement apartment in Toronto covers the Toronto side in more detail.

How much rental income can count toward your mortgage?

More than most buyers expect, if the house is owner-occupied and the mortgage is CMHC-insured. CMHC’s published rental income rules say:

Owner-occupied, two units: up to 100% of the gross rent can be added to your income.
Owner-occupied, three or four units: either up to 50% of gross rent, or the net rent after operating costs.
Not owner-occupied (a rental property): 50% of gross rent or net rent for two to four units; a one-unit rental is not eligible for CMHC insurance at all.

Under CMHC’s gross rent approach, property tax and heat for the house may be left out of the debt ratios. Each lender and insurer applies its own policy, and uninsured lenders can be stricter, so ask your mortgage broker in writing how much of the rent they will use and what proof they need, such as the lease or an appraiser’s rent estimate.

Free tool — what can you actually afford?

How much can a basement apartment lower the income you need?

A lot. Here is a worked example using Brampton’s median detached price from January to October 2026, $950,000, a first-time buyer with the minimum 5% down, and a basement lease of $1,800 a month. That rent is an example only; published rent surveys rarely separate basement units, so use the real lease.

$950,000 house, $70,000 down	No rent counted	50% of rent counted	100% of rent counted
Mortgage including insurance premium	$916,960	$916,960	$916,960
Actual payment at 4.5%, 30 years	$4,623 a month	$4,623 a month	$4,623 a month
Rent added to your income	$0	$10,800 a year	$21,600 a year
Household income needed	about $201,000	about $166,000	about $155,000

Source: my calculations from CMHC’s rental income approaches, CMHC premium rates (4.20% for 95% loan-to-value with a 30-year amortization) and the 39% gross debt service limit at a 6.5% qualifying rate. Price from TRREB MLS data via REALM, January–October 2026. The “no rent” column includes property tax at 0.8% of price and $150 of heat; the rent columns leave them out, as CMHC’s gross rent approach allows.

In this example, counting the full rent cuts the income you need by about $46,000. That is often the difference between qualifying and not. It only works if the lender accepts the unit and the rent, which is why proof of legal status matters so much.

How much down payment do you need for a house with a basement apartment?

For an owner-occupied house with one or two units, the CMHC minimum is the same as for any home: 5% of the first $500,000 and 10% of the rest, on a price under $1.5 million. For three or four units, the minimum rises to 10%. At $1.5 million and above, insurance is not available and you need 20% down.

That $1.5 million line matters here, because CMHC’s 100% rent rule applies to insured mortgages. In 2026, the median detached house was $950,000 in Brampton, $1,225,000 in Mississauga and $1,420,000 in Markham, and the median semi was $790,000 in Brampton and $885,000 in Mississauga. Semis and detached houses in these price bands can still be bought with insured financing.

What happens to a basement tenant when you buy the house?

The tenancy continues. Under the Residential Tenancies Act, the lease runs with the property, so you become the tenant’s landlord on closing, on the same rent and terms. You also take over any last month’s rent deposit, and you owe the tenant yearly interest on it at the rent increase guideline rate.

You can only ask the seller to end the tenancy for you with an N12 notice if you, your spouse, a child or parent, or a caregiver will genuinely live in that unit, and the house has no more than three units. If you plan to live upstairs and keep renting the basement, an N12 is not available for that basement unit. The seller must give at least 60 days’ notice ending on the last day of a rental period or term, and must pay the tenant one month’s rent. See tenant rights when a rental unit is sold for the tenant’s side.

One useful detail on rent: units first occupied as a residence after 15 November 2018 are exempt from Ontario’s rent increase guideline, which is 2.1% for 2026 and 1.9% for 2027. Ask when the basement was first rented.

What if the basement apartment is not legal?

You can still buy the house, but price in the risks:

Financing: a lender may not count the rent at all, which can sink your approval.
Enforcement: Brampton warns that penalties for unregistered units and construction violations can be significant, with fines it lists as ranging from $25,000 to $1.5 million and daily penalties for continuing offences.
Cost to legalize: fire separation, a second exit, ceiling height and electrical work can be expensive, and some basements cannot meet the ceiling rule without lowering the floor.
Insurance: tell your insurer about the unit; an undisclosed rental can put a claim at risk.

For a second unit added to an existing house, Ontario’s guide says development charges are not collected, which helps if you plan to legalize it properly after you buy.

My take

I tell buyers to pay for the paperwork, not the kitchen. A basement with a permit, final inspection and registration is worth more to you, because a lender can count its rent and you can rent it with confidence. Make your offer conditional on seeing those documents and on your lender confirming in writing how much rent it will use.

Watch out

Do not rely on the word “legal” in a listing. Ask for the permit number and final inspection, check the city’s registry where one exists, and have your lawyer review it before the conditions expire. If the unit turns out to be unregistered after closing, the cost and the risk are yours.

What to do next

Ask your mortgage broker how much basement rent your lender will count and what proof it needs.
Request the building permit, final inspection, electrical certificate and any registration before you offer.
Check the city’s registry or permit records for the address yourself.
Get a copy of the current lease and confirm the rent, deposit and end date.
Make the offer conditional on financing, inspection and your lawyer’s review of the unit’s status.

If the unit would house family rather than a tenant, my guide to moving a parent in covers in-law suites and garden suites, and rental income tax and Form T776 explains how the rent is taxed.

Need help with this? Talk to me.

I’m Jatin Dua, Broker of Record at RE/MAX Quantum Realty, and I’m the best agent to do this kind of work for you in Toronto and across the GTA. Over $100 million in GTA sales and 100+ families helped sell. Feel free to contact me any time: call or text 833-330-1925 or email [email protected].

Book a free call Call 833-330-1925

Frequently asked questions

Can basement rental income be used to qualify for a mortgage in Ontario?

Yes. For an owner-occupied two-unit house with a CMHC-insured mortgage, CMHC allows up to 100% of the gross rent to be added to your income. For three or four units it allows up to 50% of gross rent or the net rent. Lenders apply their own policies, so confirm the amount in writing before you firm up in 2027.

How do I know if a basement apartment is legal in Brampton?

Check the City of Brampton’s public list of registered additional residential units. Brampton requires every additional unit to be registered, including older units once treated as legal non-conforming. Also ask the seller for the building permit and final inspection. If the address is not on the list, treat the basement as not legal until the seller proves otherwise.

Do second units have to be registered in Mississauga?

Yes. The City of Mississauga says all second units must meet the Building Code, Fire Code and zoning rules and must be registered under its Second Units Registration By-law. There is no fee to register. The city publishes a Second Units Registry List, updated the second week of every month, so a buyer can check an address.

How much does it cost to register a basement apartment in Markham?

Registering a two-unit house in Markham costs $246, plus $260 for the first fire inspection, according to the City of Markham’s website in November 2026. Both units are inspected for building and fire safety. Markham says all two-unit houses must be registered, and occupying one without registering can lead to court action and fines.

What is the minimum ceiling height for a basement apartment in Ontario?

A basement second unit in an existing house can have a ceiling height of 1.95 metres, or 6 feet 4¾ inches, over the required floor area and along the route to the exit, according to Ontario’s guide to adding a second unit. Houses less than five years old must meet new-construction rules instead, so check with the local building department.

Can I evict the basement tenant after I buy the house?

Only in limited cases. In Ontario, the seller can serve an N12 on your behalf if you or a close family member will genuinely live in that unit and the house has three or fewer units. If you will live upstairs and keep renting the basement, an N12 does not apply. The seller must pay the tenant one month’s rent.

Is a house with a legal basement apartment worth more in the GTA?

Often it is worth more to buyers who need the rent to qualify, because a lender can count legal rental income. No public GTA data separates sale prices for houses with legal basement units, so compare recent sales of similar homes on the same street. A basement without permits can carry legalization costs that offset any premium.

How much down payment do I need for a house with a basement apartment?

For an owner-occupied house with one or two units priced under $1.5 million, the CMHC minimum down payment is 5% of the first $500,000 and 10% of the rest, the same as any home. For three or four units it is 10%. At $1.5 million or more, insurance is not available and you need 20%.

Do I pay development charges to legalize a basement apartment in Ontario?

No. Ontario’s guide to adding a second unit says development charges are not collected for building a second unit in an existing house. You still pay for the building permit, any fire inspection, an electrical permit, design work and construction, and you must meet local zoning rules such as parking and entrances.

Buying a Home with a Legal Basement Apartment in the GTA (2027)