Serving the GTA — Hamilton to Bowmanville
Offices in Mississauga and Milton, crews across the west GTA. Pick your area for the local rules, or call 905-749-4608 — if you're in the GTA, we build there.
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Halton & Peel
Milton
Milton is HMH Construction's home town, and it is one of the more permissive places in Halton to add a unit. Since June 2024 a serviced lot with a detached, semi or townhouse can carry up to three additional units, and since April 2025 every one of them, new or existing, has to be registered with the Town for $340. Rural Milton plays by different rules.
Milton details →Campbellville
Campbellville is a Niagara Escarpment Plan village on private wells and septic, and Milton's rural zoning now decides second units lot by lot: one unit inside the house on Escarpment Rural Area land, none on Escarpment Natural or Protection land, and no detached units anywhere the hamlet sits inside the Plan Area. Outside the hamlet, the Niagara Escarpment Commission's permit comes before the Town's.
Campbellville details →Georgetown
Georgetown is the largest community in Halton Hills, and since December 2024 the Town's zoning has allowed two additional residential units on a fully serviced lot. The floor-area caps that apply elsewhere in the house do not apply to a unit that sits entirely in the basement: it can use the whole floor. Parking, the exit, registration and the Credit River are where the real work is.
Georgetown details →Acton
Since 2 January 2025, a serviced Acton house can carry up to two additional residential units, the same Halton Hills rule Georgetown gets. What is different here is the ground under it: a mill-town grid of lots generally built before 1975, Mature Neighbourhood zoning across much of it, and Black Creek flood mapping that Credit Valley Conservation is still redrawing.
Acton details →Mississauga
Mississauga's Zoning By-law, amended by By-law 0174-2023, lets a detached, semi-detached or townhouse lot carry two additional residential units, and Article 4.1.1.2 says no additional parking is required for either. Registration of a second unit is free, and the City refunds the building permit fee once the unit passes its inspections. Ceiling height in a 1950s bungalow and the creek behind the lot are the real constraints.
Mississauga details →Oakville
Oakville's Zoning By-law 2014-014 lets a detached, semi-detached or townhouse lot carry two additional residential units, one of them detached, with a single extra parking space per unit. What limits the addition, rather than the suite, is the -0 suffix zone across the older streets south of the QEW, four heritage conservation districts and the Conservation Halton line along every creek and the lakeshore.
Oakville details →Burlington
Burlington's Residential Zoning By-law 09-2026 came into force on 2 March 2026, and its Section 5.14 lets a serviced lot with a detached, semi-detached or townhouse carry up to three additional residential units, two of which can be detached in the backyard. The first unit needs no parking space. Conservation Halton's creek valleys and lakeshore, and the Niagara Escarpment north of Highway 407, decide what your particular lot can take.
Burlington details →Hamilton
Hamilton
Hamilton's Zoning By-law 05-200 lets a single detached house in the urban area hold up to four dwelling units: two additional units inside plus one detached unit in the yard, or a straight conversion to a fourplex. Which path you take decides who reviews the permit, how much parking you need and whether a rental licence applies. Here is how the pieces fit.
Hamilton details →Waterdown
Waterdown is a belt of 2000s subdivisions wrapped around an 1879 village, still zoned under the former Town of Flamborough by-law. That by-law is friendlier than most people expect: one unit inside the house, one detached unit in the yard, no extra parking if you keep what you have. What decides your project is the ground: Conservation Halton's regulated valley along Grindstone Creek, and the escarpment edge to the south.
Waterdown details →Flamborough
Ontario's as-of-right permission for three units on a lot only applies in settlement areas with full municipal water and sewer. Rural Flamborough, where lots run on private wells and septic, falls back on Hamilton's own zoning: one additional unit inside the house, and one detached unit where the lot is at least 1.5 hectares. Servicing decides the rest.
Flamborough details →Dundas
Dundas is the Valley Town at the foot of the escarpment, incorporated in 1847 and part of Hamilton since 2001. Since 13 May 2026 it has two heritage conservation districts, and in a district a new basement entrance is an exterior alteration that needs a heritage permit before the building permit can issue. Below the town, Spencer Creek's two-zone floodplain sets its own limits.
Dundas details →Ancaster
Ancaster sits on and below the Niagara Escarpment, on the edge of the Dundas Valley. Hamilton's zoning already lets a detached house carry two internal units and a detached unit, but any lot that touches a ravine, creek or steep slope is Hamilton Conservation Authority territory, and a change that adds a dwelling unit there is a major-development permit before the building permit.
Ancaster details →Wellington County
Rockwood
Rockwood is the one fully serviced urban centre in the Township of Guelph/Eramosa: Township water, and a Township sanitary system that pumps to Guelph for treatment. That is what makes a legal basement apartment feasible here, because the zoning by-law only allows an additional unit where servicing capacity exists. The Eramosa River, GRCA lines and older stone houses are the other half of the answer.
Rockwood details →Erin
Erin's Water Resource Recovery Facility entered commissioning in July 2026, but the Town says only new developments connect as the system is built; existing homes in Erin village and Hillsburgh wait on funding and a connection by-law still being written. Until then your house is on a private septic system, and Zoning By-law 07-67 makes proving that system can carry two units the first test of any additional residential unit.
Erin details →Puslinch
Puslinch is estate-lot country on private wells and septic, and that is the fact that decides a second unit here. The Township's zoning allows two additional residential units per lot, one inside the house and one detached, but only where individual on-site water and sewage services are approved with capacity for the extra unit. The septic assessment comes before the drawings.
Puslinch details →Toronto
Toronto
Toronto's Zoning By-law 569-2013 has allowed up to four dwelling units on RD, RS and RT lots city-wide since May 2023. By-law 654-2025 lifted that to six units in detached buildings across the Toronto and East York district and Ward 23, Scarborough North, while Etobicoke, North York and the rest of Scarborough stay at four. Garden suites, laneway suites, the fire-access path and the ravine map decide the rest.
Toronto details →Etobicoke
Princess-Rosethorn, Markland Wood, Eringate and the Richview streets went up as one planned run of bungalows and splits, on lots that are wide and deep by Toronto standards. South of the Queensway the problem flips to water: smaller lots, flatter ground, real flooding history.
Etobicoke details →North York
North York is the part of Toronto that did not get sixplexes. June 2025 skipped every ward up here, so the real ceiling is four units in the house plus a garden suite, and the postwar lots out here are deep enough to take one.
North York details →Scarborough
Scarborough's south end does part of the dig for you. On lots falling toward the Bluffs or Highland Creek, through Cliffcrest, Guildwood and West Hill, you can often walk out at grade instead of cutting a stairwell, and a walkout rents better every time.
Scarborough details →York Region
Vaughan
Vaughan licenses the contractor, not just the permit. Every renovator working here needs a City of Vaughan business licence, and the City tells homeowners to phone in and verify it before they sign anything. Ask every bidder for theirs.
Vaughan details →Richmond Hill
Which zoning by-law governs your Richmond Hill lot is an open question right now. Comprehensive By-law 93-25 got only partial approval from the Ontario Land Tribunal on July 2, 2026, appeals are still live, and some lots sit under both it and an older area by-law.
Richmond Hill details →Markham
Markham Fire has to register your house as a two-unit house before the suite is legal, and a clean building inspection does not get you there. We have seen well-built Markham basements worth nothing to an insurer because nobody closed that loop.
Markham details →Durham Region
Pickering
Pickering approves a second unit twice. First the building permit, then a separate mandatory registration under By-law 8040/23, which cannot close until Fire Services and Building Services have both inspected the finished suite.
Pickering details →Ajax
Ajax is one of the easier places in the GTA to add a unit right now, and most of what you'll read online about it is out of date. In March 2025 the Town rewrote its zoning through By-law 23-2025.
Ajax details →Whitby
Right now Whitby is paying homeowners to do the exact work we do best.
Whitby details →Oshawa
In Oshawa the thing that kills a second-unit deal is almost never the basement. It's the driveway.
Oshawa details →Bowmanville
Clarington decides your Bowmanville project with a colour-coded map before anything else does. Urban Bowmanville sits in the green zone and gets two additional units; the Greenbelt lands wrapping the town get one, and a floodplain lot gets none.
Bowmanville details →Also serving: — and everywhere in between (excluding Brampton).
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