Storm Drain Installation

Storm drainage is the system of inlets, pipes, and outlets that moves surface water off your property and public rights‑of‑way to prevent flooding, erosion, and icing. In the GTA, these systems typically route runoff from paved areas, driveways, and landscaped grades into a storm sewer (also called a surface water drain) that is separate from the sanitary system. On private lots, this may include grated area drains, trench drains, or catch basins tied to a storm sewer connection or to an approved outlet.

Definition and Function

A storm drain is an inlet—usually with a grate—that collects rain and snowmelt from impervious surfaces and conveys it by gravity through underground piping to a storm sewer or approved outlet. Its primary function is to remove excess surface water quickly and safely so it does not pond against foundations, flood low spots, or sheet across walkways and drive lanes. In most systems, storm drainage is kept separate from sanitary sewage; stormwater often discharges directly to nearby watercourses or Lake Ontario, while sanitary flows go to a treatment plant. Never pour hazardous substances into storm drains, as this contaminates receiving waters.

Environmental and health considerations in the GTA:

• Water quality: Because storm sewers may discharge untreated runoff to creeks and the lake, pollutants such as oils, metals, and lawn chemicals washed from hard surfaces can enter the environment. Keep only clean rainwater in storm drains—no soaps, paints, or chemicals.
• Mosquito breeding: Catch basins can hold small amounts of stagnant water in their sumps during dry periods, creating potential mosquito habitat if not properly maintained.
• Flooding and backups: During intense storms, inlets and storm sewers can be overwhelmed, leading to street ponding and potential basement flooding. Winter snow and slush can also block grates, causing localized flooding when thaws or rain occur.

Municipal versus private responsibilities in Toronto:

• Public storm sewers and roadway drains are under municipal jurisdiction in the right‑of‑way.
• Private property owners are responsible for any storm drains and catch basins located on their lots. In Toronto, owners must keep private catch basins, storm drains, ditches, and swales free of defects and obstructions and ensure drainage does not adversely affect adjacent properties, in accordance with the Toronto Municipal Code.
• Many private storm drains on Toronto properties (notably in parts of North York and Scarborough) connect to the storm sewer that ultimately outlets to the lake, not to the sanitary system.

Important note

This brochure is informational and does not replace the requirements of the Toronto Municipal Code (e.g., Chapters 681 Sewers and 629 Property Standards), Ontario Building Code, or applicable Conservation Authority regulations. Always confirm current rules with the City of Toronto or your local municipality and consult qualified professionals before design or installation.

Storm drain systems in the GTA are built from a few core parts that move, pre‑treat, and safely discharge runoff, while meeting Canadian code slopes and local best practices for our clay soils and freeze–thaw seasons.

Key Components

• Storm sewer: The public storm network that private systems discharge to. Storm drains are distinct from sanitary sewers; keeping them separated protects treatment capacity and local waterways. Private catch basins and roof leaders that are intended for rain/snowmelt should tie to the storm sewer, not the sanitary line. [City of Toronto materials and many technical sources reinforce this separation.] [2][10]
• Catch basins and gully pots: Catch basins (with a sump below the outlet) are the first line of pretreatment, settling out grit and debris before flow enters the storm sewer. In the UK, “gully pots” are true trapped gullies designed to block sewer gases; here, most catch basins function primarily for sediment capture and do not necessarily provide gas trapping. Heavy-duty grates are used where vehicle traffic is expected. [2]
• Oil-grit separators (OGS): Specialized manhole-style chambers installed on private or commercial sites to settle sediments and separate oils before discharge to the storm sewer. They are often specified where parking lots or service areas generate oily runoff. [2]
• Roof drain: Collects water from flat or low-slope roofs and connects to the building storm system. On commercial and multi-residential roofs, the drain body is coordinated with the roofing scope; a plumbing contractor typically supplies/locates the drain and connects to storm piping per manufacturer instructions. [3]
• Sump receiver: A support component used with some roof drains to recess the drain body and provide a consistent bearing surface, improving drainage to the inlet and facilitating a proper connection to the storm piping below. [3]
• Channel and area drains: Linear channel drains for driveways/walkways and point drains for patios or low spots route surface water to the storm line or a catch basin. Residential-grade channel systems include interlocking plastic channels and grates designed for pedestrian and light-vehicle loads when set in concrete. [4][6]

Materials and Specifications

• Pipe and structures: Common materials include PVC/PE (including HDPE) for buried piping, and concrete or polymer/plastic for catch basins and channel drains. In traffic areas, frames and grates are typically cast iron or reinforced concrete to carry loads. Fibre-reinforced plastic pipes are also used in some systems. Select materials that tolerate freeze–thaw and high groundwater conditions common in parts of Toronto. [2][4][6]
• Bedding and soils: In clay-rich GTA soils, provide stable, well-compacted granular bedding and backfill around pipes and structures to maintain grade, protect joints, and limit settlement or heave. Use geotextile separators where needed to keep fines out of granulars and perforated drains. [2]
• Infiltration options: Where site plans allow on-lot infiltration (subject to TRCA/municipal approvals), infiltration trenches or soakaway pits must be matched to soil and groundwater. Typical guidance includes ensuring adequate percolation rates (e.g., >15 mm/h), maintaining setbacks from the water table/bedrock, using appropriate filter media and distribution piping, and providing pretreatment (e.g., via a catch basin or OGS). Winter operation and bypasses should be considered. [5]
• Grates and covers: Choose grates appropriate to use and safety—pedestrian-safe openings and vehicle-rated assemblies where needed. In traffic, long narrow slots parallel to vehicle or bicycle travel can be hazardous; use patterns that maintain hydraulic capacity without creating tire traps. [2]
• Minimum slopes (code-aligned): Install storm drainage piping with a minimum slope of 1:50 (2%). Where necessary, a building drain that is at least 100 mm (4 in.) in size may be reduced to 1:100 (1%) to match an existing municipal connection elevation, provided overall system performance is maintained. These slopes support self-cleansing velocities and reliable drainage. [3]
• Safety and PPE for installation: Storm drain work involves roof penetrations, excavations, and sometimes confined spaces. Follow site OHS requirements throughout installation, including:

- Pre-operational checks on tools/equipment; assess hazards and implement controls.

- Excavation safety (proper shoring/shielding, safe access/egress) and awareness of buried utilities; obtain locates before digging.

- Fall protection when working at heights; confined space procedures where applicable.

- Required PPE: hard hat, high-visibility apparel, safety boots, gloves, eye/ear protection, and respiratory protection when cutting or coring. Maintain PPE per manufacturer guidance. [3]

• Discharge and connections: Ensure downstream connection is to the storm sewer or an approved on-site facility (not the sanitary). Many sites include additional flow controls or on-site storage to reduce peak discharges to the public system, especially on larger properties. Coordinate outlet type and any pretreatment devices with the site plan. [2][10]

Practical GTA note: For clay backyards and high water tables found in parts of Etobicoke and Scarborough, prioritize durable materials, stable bedding, and accessible pretreatment (catch basin sumps/OGS) so maintenance crews can remove silt regularly and keep systems performing through spring thaws and summer downpours. [2]

For GTA installations, plan the work to suit local conditions (heavy clay soils, freeze–thaw, and municipal requirements). Keep stormwater connections separate from sanitary, and ensure runoff is directed so it does not adversely affect adjacent properties, consistent with Toronto Municipal Code expectations for stormwater-only connections and property standards.

Step-by-Step Workflow

1) Pre-job safety and tool checks

• Conduct pre-operational and safety checks on all tools, equipment, and machinery per manufacturer specs and site procedures. Identify OHS hazards, assess risks, and implement controls before starting work. Ensure suitable PPE is selected, used, and maintained throughout the job.

2) Layout and slope

• Set elevations and confirm fall. Install drainage piping with a minimum slope of 1:50. Where necessary to meet the invert of an existing municipal connection, a 100 mm (4 in.) building drain may be reduced to 1:100, if permitted by code. Verify clear discharge routing for stormwater-only flows under Toronto bylaws.

3) Roof drain assembly at the deck

• Place the roof drain body in the roof opening and secure it with the underdeck clamp. If specified, set the sump receiver flush with the supporting edges of the drain body. Install the waterproof membrane over the sump receiver and drain body per the roofing specification.
• Fit the clamping collar and bolt it through the drain body to clamp the roof membrane, creating a watertight seal. Install the dome into the clamping collar and twist-lock it into the retaining clips.

4) Piping connections

• Connect to the storm drainage piping sized and sloped per design. Maintain the minimum slopes above and support the pipework per the material manufacturer’s instructions. On commercial projects, the roofing contractor typically installs the roof drain; the plumbing contractor supplies and locates it—always follow the drain manufacturer’s installation manual to ensure weather-tightness at the penetration.

5) Cold-climate provisions (GTA freeze–thaw)

• Inlet/outlet details should remain functional under ice conditions. Where applicable, avoid submerged inlets, consider larger minimum pipe diameters for exterior conveyance, and ensure overflow provisions are in place to pass design flows during winter conditions.

6) Commissioning and basic checks

• Water-test the assembly. Confirm the clamping collar fully seals the waterproof membrane and that the dome is secured. Reconfirm slopes to outlet. Complete a final safety sweep: remove temporary shoring, tools, and debris; leave grates and inlets clear. At handover, remind the owner that private catch basins/drains must be kept free of defects and obstructions under Toronto’s property standards.

7) Self-Check and resources

• Complete Self-Test D-3.5: Installing Storm Drainage Systems. If using a printed copy, find the self-test and answer key at the end of the section; scan the QR code for the interactive Self-Test.

On-site Safety Checklist

• OHS compliance: Follow the Occupational Health and Safety Regulation at all phases. Address hazards related to working at heights (roof work), excavations, and confined spaces; implement appropriate controls before proceeding.
• Pre-operational checks: Inspect tools/equipment daily; verify guards, power cords, ladders, and access/egress are safe and serviceable.
• PPE: Select, use, and maintain suitable PPE for the task and environment. Replace damaged PPE immediately.
• Fall/excavation controls: Use fall protection when required; provide trench support/shoring and safe access when working in excavations.
• Confined space controls: If entry is unavoidable, follow a confined space procedure (hazard assessment, ventilation, monitoring, rescue plan) before entry.
• Slope and sealing verification: Confirm minimum pipe slopes (1:50; or 1:100 where permitted for 100 mm/4 in. building drains). Verify the roof drain’s clamping collar fully seals the waterproof membrane; ensure dome engagement is secure.
• Winter readiness: For exterior conveyance components, avoid submerged inlets, size outlets to function under ice, and verify overflow paths.
• Handover condition: Leave all drains and grates unobstructed. Remind owners that private stormwater features must be maintained free from defects and obstructions per Toronto property standards. For learning reinforcement, complete Self-Test D-3.5 and use the interactive resources provided in that module.