If you are pricing a basement apartment in Mississauga, you have probably filed the approvals under cost and the renovation under real spend. It runs closer to the other way around. The City refunds the building permit fee once an additional residential unit is built and inspected, its own incentives table shows second and third units exempt from city, regional and GO Transit development charges, and putting the finished unit on the City’s registry costs nothing.
What you are paying for is everything the unit has to be before any of that applies.
What the City has to be satisfied of before it registers your unit
Mississauga’s Second Units Registration By-law 0114-2016 is short and worth reading once in full. It says every person who establishes, operates or permits the occupancy of a second unit shall register it. That is not an offer.
Before the Registrar registers anything, section 13 requires satisfaction on the Ontario Building Code, the Ontario Fire Code, the Ontario Electrical Safety Code as required by the Fire Code, the City’s zoning by-law, and the registration by-law itself, plus any other applicable law. Section 14 puts the weight where it changes your budget: the owner bears the onus of proving the unit meets those requirements to the Registrar’s satisfaction. Submitting the application consents to an inspection. If the requirements have not been met eighteen months after the Registrar receives your application, it can be deemed abandoned. Where the Registrar refuses or revokes, the by-law says that decision is final.
The by-law names Zoning By-law 225-2007, and Mississauga consolidated most of its low-rise residential zones in 2025, so confirm the zoning actually in force at your address rather than the number printed in a 2016 document. ADU regulations in Mississauga sets out how those layers sit together.
The part people underestimate is the penalty. Contravening the by-law, including an order made under it, is an offence, and a person found guilty under Part III of the Provincial Offences Act is liable to a fine of not more than $25,000, or $50,000 for a corporation. That is the number sitting behind an unregistered unit somebody is living in.
The measurement that decides whether this is a renovation or an excavation
Go downstairs with a tape before you go anywhere else.
Ontario’s guide to adding a second unit to your house addresses a detached, semi-detached or rowhouse more than five years old, and for that house it says a basement second unit is permitted a ceiling height of 1.95 m (6 feet 4¾ inches) over the entire required floor area, including the route inside the unit leading to the exit. Both halves of that sentence do work: the whole required area, and the path out of it. The guide also notes that if your house is less than five years old, different Building Code rules apply and directs you to your local building department, so a newer Mississauga build does not get to use the figure at all.
Work from the underside of the joists downward: a finished ceiling, and any ducting or plumbing routed beneath them, come off the number before you compare it to 1.95 m. Fall short anywhere in the required area, or along the route out of it, and the project changes category. Underpinning or lowering the floor brings in excavation, engineering and a longer schedule, and moves the job from one that fits inside a normal renovation budget to one that does not. Which ADU type suits your property runs the same measurement as a shortlisting tool if the basement is not yet settled.
What each of the other requirements does to the budget
None of these are optional, and none are expensive in isolation. They get expensive in the wrong order, after the drywall is up.
- Egress. Where the exit from one unit leads through the other, a second means of escape has to be provided by a window. For a basement the guide specifies a minimum unobstructed opening of not less than 0.38 sq m (4.1 sq ft), an openable portion of 460 mm (18 inches) or more, and a maximum of 900 mm above the floor or steps. In an existing foundation that means cutting the wall, building a window well outside it, and finding somewhere for it to drain.
- Fire separation. The Code requires a 30-minute fire separation between units and between units and common areas, and the guide says it can be reduced to 15 minutes if the entire house has interconnected smoke alarms. Ordinary materials and ordinary labour while the ceiling is open, which is why it belongs in the first version of the drawings rather than the second.
- Heating. One furnace and a shared duct system is allowed, but it has to carry a duct-type smoke detector meeting the UL 268A standard that shuts off fuel and power to the furnace when it trips. The guide separately suggests a second furnace if you would rather not share odours, noise and one thermostat between two households, a comfort decision with a real price attached.
- Plumbing. Each unit needs its own water shut-off valves, and a backwater valve may be required where the area is subject to flooding or sewer backup. Mississauga’s fee schedule prices the residential backwater valve permit item at $50.00, which tells you the permit is trivial and the trenching is not.
- Electrical. A separate electrical permit is required and the Electrical Safety Authority inspects the work, on its own timeline alongside the building permit rather than inside it.
- Room sizes. The Code sets minimum floor areas, including 13.5 sq m (145 sq ft) for combined sleeping, living and dining areas and kitchen space in a bachelor unit. This is where a small basement quietly stops being a two-bedroom.
Construction cost itself is driven by which of these your basement fails, not by the square footage. What an ADU costs in Ontario carries the sourced ranges and what moves them.
What a basement apartment permit costs in Mississauga, and how much comes back
This part is knowable in advance, because Mississauga publishes it all.
The Building Division fee schedule, effective February 1, 2026 to January 31, 2027 under Building By-law 0236-2024, calculates a permit fee as a service index multiplied by the floor area in square metres. The index for an additional residential unit within an existing building is $11.33 per square metre, with the minimum residential fee applied on top per the schedule, and residential work within Part 9 of the Building Code is never charged less than $244. On a 65 sq m unit, about 700 sq ft, the index alone lands near $740. There is also a $50 electronic pre-screening fee the schedule describes as non-refundable. The City calculates the real total once it pre-screens your request.
Then it gives the permit fee back. The City’s additional residential units page says the building permit fee is automatically refunded once the unit is constructed and all building inspections are complete, by cheque in the mail.
Registration is free. The City’s registering a second unit page says so directly, and in the same breath names what is not: a building permit, fire inspection fees, and any professional design work and renovation the unit needs. The fire inspection has a published number. Under Schedule H of the Fire and Emergency Services fees, effective January 1, 2026, a paid residential Group C inspection of a single family residence of one to two floors is $184.53 per inspection plus 13 percent HST, and a repeat follow-up inspection on a violation is $96.21. These schedules are re-set annually, so confirm the current figures before budgeting on them.
The one charge that can still be payable
Mississauga’s own pages describe development charges two different ways. The additional residential units page says they will also apply for additions and garden suites; the pre-approved garden suite plans page says some development charges will also apply. Neither sentence is about a unit built inside the existing house, which is neither an addition nor a garden suite.
The itemised version is the City’s Gentle Density Incentives Table, published in April 2026, which runs the charges line by line for basement units, garden suites and triplexes as second and third units. It shows the building permit fee refunded, parkland cash-in-lieu exempt under the Planning Act, and the city, regional and GO Transit development charges all exempt under the Development Charges Act. One row reads differently: the school board development charge, listed as may be payable.
That wording is precise rather than vague. Education development charges are levied by school boards under the Education Act, not the Development Charges Act, so the exemption clearing the other rows does not reach them, and Peel’s boards do levy them. The current combined residential rate is $5,676 per dwelling unit from July 1, 2026 to June 30, 2027, rising each year under the boards’ 2024 by-law.
The reason most basement apartments still do not pay it is that the boards’ own by-law carries residential exemptions. The by-law text the Peel District School Board published with its 2024 report does not impose the charge on the creation of one or two additional dwelling units in an existing single detached dwelling, or one additional unit in an existing semi-detached, row or other residential building. Two conditions sit under it. The exemption falls away if the additional unit’s gross floor area exceeds that of the existing single detached dwelling, or, in a semi-detached, row or other residential building, the existing unit or the smallest unit already in it. The second is a definition: an additional dwelling unit is one whose building permit application comes no sooner than twelve months after the existing dwelling was occupied. Gross floor area is counted on floors above the average level of finished ground, so ask the City how it counts a basement. That second one is what makes a very new house a different conversation. The City works out what is actually payable when it pre-screens the application, so take the number from them rather than from any page, this one included.
If the unit is already down there and nobody ever pulled a permit
This is the most common version of the question in Mississauga, and the order of operations decides how it goes.
The permit comes first. The City’s registration page is explicit that if a permit was not obtained you apply for one, and the registry sits downstream of that rather than substituting for it. So the sequence runs: a permit application for work that already exists, drawings that reflect what is actually there, whatever remediation the review turns up, inspections, the fire inspection, then registration. The registry list is public and the City updates it in the second week of every month, so a unit’s status is not a private matter.
Budget for the discovery, not the drawings. A unit built without a permit was built without a fire separation anyone checked, without an inspected escape window, and often without an ESA-inspected panel. Those are the same requirements as a new build, reached by opening finished work instead of working in an open ceiling, which is why legalizing usually costs more per square foot than doing it once. The fee side is identical: the City’s ARU page says permit fees are refunded when you are building or legalizing an ARU.
A registered unit can be tenanted. What it rents for is set by the local market, and how that income is taxed is a question for your accountant.
Where the calendar turns into money
Mississauga publishes its own timelines on the building permit cost and time frames page. Pre-screening takes about 7 to 10 business days, the first review of a complete second unit application may take 15 business days, and the City’s stated average for actually obtaining a second unit permit is 10 weeks. Each resubmission cycle could add two or more weeks with no guaranteed review time, because resubmissions are not subject to the legislated windows.
That is where the weeks go, and it is the argument for a qualified designer. A resubmission cycle costs more in carrying time than better drawings ever would.
What to do this week
Two things, both free.
Measure the height to the underside of the joists in every part of the basement the unit would occupy, including the route to the exit, and write the numbers down. That tells you whether you are looking at a renovation or an excavation, and nothing you decide afterwards is worth much until you know.
Then find out what the City already has on file for your address. Mississauga lets you search building permit history by address, and the second units registry list is public. Whether a previous owner pulled a permit for finished basement space is the first thing any designer working on an additional unit will ask for, and the thing most likely to change what the project turns out to be. Start there, not with drawings.
