Gutters in Montreal | Bylaw 20-030 Compliant
Montreal is an island, and the City says so itself: a highly urbanized territory with extensive impervious surfaces, where rainwater has little opportunity to infiltrate the ground. Water falling on a roof therefore has virtually nowhere to go except the street and the sewer system. The City monitors water levels in the St. Lawrence River and Rivière des Prairies, and has identified areas such as Ahuntsic-Cartierville, L’Île-Bizard–Sainte-Geneviève, Lachine, Montréal-Nord, Pierrefonds-Roxboro and Rivière-des-Prairies–Pointe-aux-Trembles as vulnerable to flooding. In August 2024, the remnants of Hurricane Debby brought record rainfall, widespread basement flooding and sewer backups: the costliest weather event in Quebec’s history. Here, a gutter does not decorate a façade: it determines where roof water ends up.
The Core Issue: Article 120 of Bylaw 20-030
Montreal enforces Bylaw 20-030, Article 120 of which directly affects gutters. It applies to buildings where stormwater is drained using exterior gutters and downspouts. For any building where the permeable area exceeds 20% of the building roof area, roof stormwater must be directed toward the property’s permeable surfaces.
In practical terms: roof water is supposed to end up where it can be absorbed—on a lawn, planting bed or permeable ground—not disappear into an underground pipe. Water that does not infiltrate the property enters the system, at the same time as water from the entire surrounding area.
Three clarifications. First, the article includes an application condition based on the proportion of permeable surface relative to the roof: not every Montreal property is in the same situation, and any statement claiming “in Montreal, every gutter must…” would be inaccurate. Second, we do not reproduce the full text of the article or the requirements it details here: for the scope of application at your address, those requirements and any authorization that may be needed, the City directs residents to their borough—it is there that you must confirm the requirements before work begins, and that response is authoritative. Finally, this is a City of Montreal bylaw: the island’s related cities have their own.
A City of Plexes: What That Means for Your Roof
Montreal is a city of plexes and low-rise apartments, not bungalows. Statistics Canada’s 2021 Census is clear: the housing stock is dominated by duplexes and buildings with fewer than five storeys, while detached single-family homes are a minority. It is also an older housing stock: two thirds of dwellings date from before 1981, and more than one third from 1960 or earlier. This has four implications for gutter selection.
Flat Roofs, Few Outlets
Montreal plexes commonly have flat roofs. Where exterior gutters are present, each one receives runoff from a large share of the roof area. This is the typical situation in which a five-inch channel with a single outlet reaches its limit: 6-inch gutters and an additional downspout increase flow capacity.
Row Housing, No Side Margins
You cannot install a downspout just anywhere: on attached homes, discharge points are limited—front façade, laneway or backyard. The location is determined on the building, by considering what is on the ground below.
Two to Four Storeys, Not Single-Level
Downspouts are long, fasteners are under greater strain, and access affects installation as much as future maintenance.
A Housing Stock Mostly Built Before 1981
On these buildings, downspouts have historically been connected to the internal drainage system. What is found once the area is opened up does not always match what is visible from the street: we verify before providing a quote.
Our Services in Montreal
Installation and Replacement
Installation of seamless aluminum gutters, gutter installation and 6-inch sizing when roof flow requires it.
Downspouts and Protection
Gutter downspouts, leaf guard installation and gutter protection against ice dams.
Maintenance and Repair
Gutter cleaning, repair and inspection before concluding that everything needs to be replaced.
Around the Roofline
Soffits and fascias, aluminum capping and caulking.
Exterior Siding
Exterior siding and exterior insulation, when the walls are opened at the same time.
What We Check On Site
| Point Checked | What We Look At |
|---|---|
| Fascia | A gutter is only as secure as the board to which it is attached. In an older building, this is often the real issue: waterlogged wood behind capping, screws that no longer hold. |
| Channel slope | The channel must drain toward its outlet. Standing water deposits sediment, freezes in winter and adds weight to the line. Slope is checked with an instrument, not by eye. |
| Outlets | We assess how much roof area drains into each downspout and where it can actually run given the attached construction. This calculation determines whether an additional outlet or a wider channel is needed. |
| Ground clearance | Where the water reaches the ground and where it goes next: the slope of the ground against the wall, the type of surface it is directed toward, and what lies beneath the discharge point. A staircase or sidewalk soaked in the afternoon becomes a sheet of ice in the evening. |
Contact Us
Gouttières et Revêtements Synergy is based at 580 Chem. de Lavaltrie, local 103, Lavaltrie QC J5T 0H1. We hold RBQ licence 5723-4940-01, are Alu-Rex ÉLITE Installer, CAA-Québec Recommended and APCHQ Certified.