Most Waterdown Lots Can Carry a Second Unit. Grindstone Creek and the Escarpment Decide the Rest.

Which by-law governs a Waterdown lot, and what it allows

Waterdown was part of the Town of Flamborough until the 2001 amalgamation, and that still matters. The City of Hamilton Act carried the former municipalities' zoning by-laws forward until Council amends or repeals them, so Flamborough Zoning By-law 90-145-Z, enacted in November 1990, is the by-law most Waterdown houses sit under. When Hamilton rewrote its second-unit rules on 8 June 2022 it passed a matching amendment for each former municipality: By-law 22-135 for Flamborough, and By-law 22-132 for the city-wide By-law 05-200, which also renamed the units "additional dwelling units". The Flamborough text still says "secondary dwelling unit"; the substance is the same.

In the R1, R4, R5, R6 and UC zones, a single detached, semi-detached, link or street townhouse may contain one secondary dwelling unit, and the same lot may also carry one secondary dwelling unit – detached. Parking is the part people get wrong: no additional parking space is required for either unit, provided the spaces that existed for the house on 12 May 2021 are kept, and up to two spaces for the unit may sit in the required front yard. The limits that shape a basement suite are about the façade — a maximum of one entrance on the front of the house, and no outside stairway above the first floor other than a required exit — which is why the new door normally goes on the side or the rear.

Zoning by-laws get amended, and the current city-wide detail lives on our Hamilton page. Confirm your lot's zone with the City before you draw anything.

Grindstone Creek: what Conservation Halton regulates

Grindstone Creek runs through Waterdown and over the escarpment at Great Falls, and Conservation Halton is the authority on it. Under Ontario Regulation 41/24 the authority regulates all watercourses, valleylands, wetlands and hazardous lands, plus the lands adjacent to them, and a permit is required before any development inside that regulated area. Its policy document, last amended 21 June 2024, classes the Grindstone valley as a "major valley system" and prohibits development within 15 metres of the stable top of bank, within 15 metres of the flood plain or meander belt where no valley is apparent, and within 30 metres of a wetland, unless a specific policy allows it. It also runs a One Zone Concept: the whole flood plain is floodway.

Two definitions matter. "Development" includes any change to a building that increases the number of dwelling units, so a basement apartment on a regulated lot needs Conservation Halton's permission even when nothing changes outside. It also includes site grading and placing or removing material, which is what a walkout excavation is. Many Waterdown lots are well clear of the creek; the ones that back onto its valley, or onto the tributaries and wetlands that feed it, should be checked on the authority's online mapping before anyone pays for drawings.

Getting a Conservation Halton permit on a Waterdown lot

Where a house already stands within 15 metres of a flooding or erosion hazard, an alteration or addition may be permitted only if it does not alter the use or potential use of the building. Work that adds a unit does alter it, so that work is assessed as a new building, which must sit at least 6 metres from all hazards and be graded so it creates no new hazard for the neighbours. Decks, sheds and other non-habitable structures have a policy of their own.

The mapping shows approximate areas, so pre-consult. The authority confirms whether an application is complete within 21 days, aims to finish its review within four weeks once it is, and works to a legislated 90 days. Its permission does not replace the City's permits, and permits are issued to the current landowner and cannot be transferred on a sale, which matters if you are renovating to sell.

One local detail shows how closely this creek is watched: upstream at Millgrove, the Grindstone Creek culvert under Highway 6 cannot pass the Regional Storm, so it backs water onto land that would otherwise stay dry, and Conservation Halton carries a site-specific flood fringe policy for that settlement. Expect the same rigour on the Waterdown reach.

The escarpment edge and the Niagara Escarpment Commission

South of the village, Grindstone Creek falls over the Escarpment in a series of waterfalls into a deeply incised valley; Smokey Hollow, the old mill site on the creek, is listed in the Niagara Escarpment Plan as an escarpment access. Development inside the Commission's Area of Development Control may require a Niagara Escarpment Development Permit, judged on landscape and natural environment. The Commission's interactive map shows whether a property is in the Plan Area or the Area of Development Control; check the brow lots along Waterdown's south edge.

Inside Development Control, exemptions decide the job. Interior work is exempt only where it does not change the use of the building, and adding a secondary dwelling unit is named as a change of use, so a basement suite needs a Development Permit. An accessory structure is exempt up to the lesser of 5 per cent of the lot or 72 square metres and 4.5 metres high, but creating a dwelling unit or any habitable space in one is not. Additions are exempt where all additions together stay at or under 93 square metres, no taller than the original house, and at least 4.5 metres from the side lot line, 7.5 metres from the rear and 15 metres from the front.

The Plan, consolidated 11 March 2026, allows one secondary dwelling unit on an existing lot of record only inside the house or an addition, never in a detached accessory building, and subordinate in size. On an escarpment lot a garden suite is off the table; a basement suite is an application.

Two Waterdowns: the 1879 village and the subdivision belt

Waterdown was severed from East Flamborough and incorporated as a village in 1879, then absorbed into Flamborough in 1974 and Hamilton in 2001. It held about a third of Flamborough's 37,796 people at the 2001 census; by 2021 it was roughly 24,400, after 28.9 per cent growth between 1996 and 2001. Most of that housing arrived as planned subdivisions: the Urban Hamilton Official Plan carries four Waterdown secondary plans — West Waterdown, Waterdown North, Waterdown South and the Waterdown Community Node — and Waterdown South's includes a Natural Heritage System and Natural Hazard Features map.

The core is different. Waterdown has 121 heritage-designated properties, most in the Mill Street Heritage Conservation District. Designation does not stop change, but the City manages physical changes through the Heritage Permit process, and 13 more non-designated properties in the village study area sit on the Municipal Heritage Register, which requires 60 days' demolition notice. The Community Node Secondary Plan, adopted 13 April 2022 as Official Plan Amendment 165, aims to protect the heritage characteristics of the historical downtown; the heritage study area runs roughly from Mountain Brow Road to Parkside Drive and from Hamilton Street to First Street.

Below grade they differ. In our experience a poured foundation from the 2000s onward usually clears the Building Code's 1.95-metre basement ceiling with room to spare, and lots that fall toward the creek often have the grade for a walkout. Stone and rubble foundations in the village rarely give that height without underpinning, and any exterior change on a designated house is a heritage conversation first.

Permits, the Building Code and how HMH sequences the work

Ontario requires a building permit to add a second unit, and the Building Code sets the floor: a 30-minute fire separation between units and between units and common areas; a basement ceiling of at least 1.95 metres over the whole required floor area, including the route to the exit; safe exits, with escape windows large enough for a person to get through and openable without tools; smoke alarms; carbon monoxide alarms where the house has a furnace burning natural gas, propane or a similar fuel; and an Electrical Safety Authority inspection of the new electrical work.

Order matters. Where a lot is regulated by Conservation Halton or sits in the Commission's Area of Development Control, those permissions come first: the authority's permission does not replace the City's permits, and an NEC exemption does not relieve you of the Building Code or the conservation authority. The City then checks the drawings against the Flamborough by-law's second-unit rules before issuing the permit.

HMH Construction is a licensed, WSIB-covered residential general contractor with offices in Milton, northeast of Waterdown, and Mississauga. Separate basement entrances and walkouts are our specialty: we handle the engineering, permit drawings, excavation, waterproofing and inspections, and the entrance itself is built in three days. Behind the door we design and permit legal basement apartments, garden suites, garage conversions and multi-unit conversions, and we build kitchens, bathrooms, finished basements, whole-home renovations, home additions and second-storey additions, and commercial fit-outs. On a Waterdown call we start with the map — zone, creek, escarpment, heritage — and tell you what your lot will carry.