Why does my renovated bathroom have a sewer gas smell when it rains in Vancouver?

Sewer gas smells in renovated bathrooms during Vancouver's rainy season typically indicate a problem with your plumbing vents or trap seals, often caused by improper installation during the renovation or blockages that developed afterward.

The most common culprit is a blocked or improperly installed plumbing vent. During your bathroom renovation, if the vent stack wasn't properly reconnected or if debris got into the system, it can't equalize pressure in your drain lines. When Vancouver's heavy rains hit (we get over 1200mm annually), water rushing through the municipal storm system creates pressure changes that can suck water out of your P-traps — those curved sections under sinks, tubs, and showers that normally hold water to block sewer gases. Without that water seal, gases flow directly into your bathroom.

Dry P-traps are another frequent issue, especially in guest bathrooms or secondary fixtures that weren't used during or immediately after renovation. If a fixture sits unused for weeks, the water in the trap evaporates, eliminating the gas barrier. Vancouver's wet climate can actually accelerate this through humidity changes and pressure fluctuations during storm systems.

Poor workmanship during renovation can also create problems. If your contractor didn't properly seal drain connections, installed incorrect trap configurations, or damaged the vent system during demolition, you'll get intermittent sewer gas intrusion that's worst during heavy rains when the municipal system is under stress. The BC Building Code (BCBC 2024) requires specific trap and vent configurations — shortcuts during renovation often cause these exact symptoms.

Metro Vancouver's aging infrastructure compounds the problem. Many neighborhoods have combined sewer systems that handle both sewage and stormwater. During heavy rainfall, these systems can back up or create pressure surges that exploit any weakness in your home's plumbing connections.

When to call a professional: This isn't a DIY fix. You need a licensed plumber to diagnose whether it's a venting issue, trap problem, or connection failure. In BC, plumbing work requires proper licensing and inspection. The plumber should smoke-test your system to identify exactly where gases are entering, check all trap seals, and verify your vent stack is clear and properly connected.

Immediate steps: Run water in all bathroom fixtures to refill any dry traps, ensure bathroom exhaust fans are working properly, and ventilate the space. If the smell is strong or persistent, this could indicate a serious sewer line issue that needs immediate attention — don't ignore it, as sewer gases can be hazardous to your health.