Stormwater in Divided Co-ownership: Quebec Municipal Duties

Heavy rainfall events are becoming more frequent. For a divided co-ownership, properly evacuating stormwater is an operational and financial concern. Several municipal requirements apply, including permitted connections, roof drain maintenance and retention requirements. The board of directors must ensure that the building complies with local by-laws while protecting the common portions and controlling common expenses. This article provides an overview (updated as of 2026-07-24) and proposes a practical action plan for your syndicate.

In short, the syndicate has a legal duty to maintain the building and comply with municipal by-laws. Many cities prohibit directing gutters or sump pumps into the sanitary sewer. They require a connection to the storm sewer, or infiltration/retention on the property. We explain these requirements and how to comply with them without budget surprises.

1) The legal framework: the syndicate’s duties and municipal powers

• Code civil du Québec (C.c.Q.). The syndicate’s mandate is to ensure the preservation, maintenance and administration of the common portions (see section 1039 C.c.Q.). Co-owners must contribute to the common expenses related to these obligations (see section 1064 C.c.Q.). These principles cover, among other things, the building’s drainage systems, roofs and sewer networks.
• Municipal by-laws. Municipalities in Quebec may prohibit connecting stormwater to the sanitary sewer, require backwater prevention devices, require source control (retention/detention), or regulate runoff at the front of a property. Your obligations vary by city (Montreal, Longueuil, Laval, etc.), but the objective remains to reduce overflows and backups.
• Technical codes (plumbing and construction). Technical requirements govern gutter outlets, roof drains, backwater valves and connections to public networks. Work must be performed by qualified contractors and comply with the standards in force.

Useful references:
– LégisQuébec – Code civil du Québec, section 1039: preservation of the building (see https://www.legisquebec.gouv.qc.ca/fr/document/lc/CCQ-1991#art_1039)
– LégisQuébec – Code civil du Québec, section 1064: contribution to common expenses (see https://www.legisquebec.gouv.qc.ca/fr/document/lc/CCQ-1991#art_1064)
– RBQ – Backwater prevention devices: best practices (see https://www.rbq.gouv.qc.ca/domaines-dintervention/plomberie/antirefoulement.html)

2) Storm sewer vs. sanitary sewer: permitted connections (and prohibited ones)

The main rule: rainwater must not be sent to the sanitary sewer. The sanitary sewer is intended for wastewater, not water from roofs, balconies or yards. Here are the key points commonly found in municipal by-laws in Quebec:

• Gutters and downspouts. Ideally, they should discharge to the storm sewer, an infiltration well, a drainage trench or a vegetated surface, depending on the property’s capacity. Discharge to the sanitary sewer is generally prohibited.
• Sump pumps. They are used to evacuate clear water (groundwater, infiltration) and must not discharge into the sanitary sewer. Discharge should be directed outdoors, to a storm drain or to a compliant infiltration system.
• Flat roof drains. They must be connected to the storm sewer with flow-control devices, or directed to an on-site retention solution (green roof, retention basin) where required.
• Backwater and anti-backup valves. A backwater valve on exposed connections helps prevent sewer backups during storms. It must be inspected and maintained periodically.

For existing buildings, it may be necessary to disconnect non-compliant connections. Some municipalities require a certificate or conduct targeted inspections after backup events.

Resources:
– RBQ – Backwater prevention and sewer backups: prevention and maintenance: https://www.rbq.gouv.qc.ca/domaines-dintervention/plomberie/antirefoulement.html
– RBQ – Plumbing: roof drainage and technical requirements: https://www.rbq.gouv.qc.ca/domaines-dintervention/plomberie.html

3) Source control: roofs, parking areas and landscaping

Cities favour “source control” to reduce runoff. In a divided co-ownership, this involves:

• Roofs and terraces. Possible installation of roof drains with flow control, green roofs or membranes providing temporary retention where technically feasible. Drain grates must remain clear.
• Parking areas and garage ramps. Sumps with baskets, catch basins and separators (where there is a risk of hydrocarbons). Discharge goes to the storm sewer, never the sanitary sewer. In indoor garages, check for the devices required by local regulations.
• Ground-level landscaping. Infiltration solutions include vegetated swales, permeable pavers, drainage trenches and retention basins. These features require professional design when they affect flow rates.
• Common portions vs. private portions. Roofs, gutter outlets and underground networks are generally common portions. Balconies, private terraces or air conditioner outlets can affect water flow; their control falls under the by-laws of the immovable (slopes, diverters, retention containers). Make sure the declaration of co-ownership and the by-laws clearly set out permitted uses.

All of this must be incorporated into the maintenance logbook/EUC, with realistic cleaning and inspection schedules.

Practical reference:
– RGCQ – Best practices for co-ownership maintenance and maintenance logbooks: https://rgcq.org/

4) Maintenance and inspections: structuring the maintenance logbook / EUC

Regular maintenance limits backups, erosion and foundation damage. The board of directors must plan, arrange and document the work (minutes, work orders, photos). Here is a framework of typical tasks to include in the maintenance logbook/EUC:

Keep the reports in the co-ownership file and record maintenance decisions in the board of directors’ minutes or the annual general meeting minutes, as applicable. In the event of a claim, this documentation facilitates indemnification and demonstrates your diligence.

5) Budget, common expenses and work planning

The adjustments required by municipal by-laws (disconnecting gutters, adding backwater valves, installing infiltration features) cost money. To avoid unpleasant surprises:

• Assess the risks and compliance. Have an engineer or specialized contractor perform a stormwater assessment. Request prioritized recommendations.
• Plan the financing. Include recurring work in the operating budget (common expenses) and major replacements/additions in the contingency fund, where appropriate. Co-owners’ contributions are based on the relative value of their fractions (see section 1064 C.c.Q.).
• Sequence the work. Group roofing, masonry and drainage work to take advantage of economies of scale and limit the need for multiple scaffold setups.
• Communicate early. Present the compliance status, options and financial impacts to the board of directors and then to the annual general meeting to obtain the necessary authorizations.

Need help budgeting and phasing your work? See our management and operations services: operations management services and financial management.

6) Road map for your board of directors: from audit to compliance

• Map the drainage routes. Where do the roofs, balconies, driveways and pumps drain? Identify discharge points and connections to the building.
• Check local prohibitions. Without citing every by-law, assume that the sanitary sewer is off-limits for clear water. Confirm the retention/detention and backwater prevention requirements.
• Order a technical inspection. A licensed plumber and/or engineer will assess the plumbing, backwater valves, sumps and storm sewer capacity.
• Prioritize corrections. Start with safety and compliance (disconnections, backwater valves), then optimization (infiltration, permeable pavers), followed by aesthetics.
• Update the maintenance logbook/EUC. Define schedules and responsible parties. Add technical data sheets and warranties to the file.
• Plan the call for tenders. Use clear specifications, a licensed contractor and a schedule that falls before the rainy seasons.
• Monitor and document. Keep quotes, photos and warranties. Record decisions in the board of directors’ and annual general meeting minutes and communicate them to co-owners.

To structure this process, also see our “Who We Are” page and our “Condominium Management in Montreal” approach: learn more. You can also browse the multiRent blog for related guides.

Frequently asked questions (FAQ)

• Can gutters be connected to the sanitary sewer? No, this is generally prohibited. Downspouts must discharge to the storm sewer, an infiltration system or a compliant retention solution. Check your city’s requirements.
• Who pays for compliance work? Corrections involving common portions are financed by co-owners through common expenses; major additions may come from the contingency fund. Private portions must comply with the by-laws of the immovable if their installations affect water flow.
• Is a municipal permit required to disconnect or add a backwater valve? Often, yes. Several municipalities require a permit or a work declaration, particularly when connections are modified. Check before starting work.

Additional resources:
– LégisQuébec – Code civil du Québec, section 1039 (preservation): https://www.legisquebec.gouv.qc.ca/fr/document/lc/CCQ-1991#art_1039
– LégisQuébec – Code civil du Québec, section 1064 (common expenses): https://www.legisquebec.gouv.qc.ca/fr/document/lc/CCQ-1991#art_1064
– RBQ – Plumbing (general) and requirements: https://www.rbq.gouv.qc.ca/domaines-dintervention/plomberie.html
– RGCQ – Advice on managing and maintaining co-ownership buildings: https://rgcq.org/

This article provides general information and does not constitute legal advice. Consult a lawyer or notary regarding your situation.

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