Basement Flooding in Markham: Why New Houses Flood Too, and What the Fixes Are

Why a newer house floods

A subdivision’s sewers are designed for a storm of a certain size, and Markham has seen larger ones. When the storm sewer and the sanitary sewer surcharge, the water looks for the lowest opening, which is your basement floor drain. Newer houses make it worse in two ways: the basement is finished and deep, and the weeping tile around the foundation is often connected to the sewer, so it adds groundwater to a system that is already full. Sump pumps installed by the builder sit in a pit that may never have filled, and the first time they are needed is the first time anyone learns they do not work.

Surface water is the other newer-house problem: lots graded by the builder settle over the first decade, and the ground ends up sloping toward the foundation and the window wells.

What the fixes do, and what the City has offered

A backwater valve is a one-way flap on the sanitary lateral that closes when the sewer surcharges so sewage cannot flow back into the house; while it is closed nothing in the house drains, which is why plumbers say not to run water during a storm. A sump pump with a pit collects groundwater from the foundation drain and pumps it outside instead of into the sewer; a battery backup keeps it running through the outages that arrive with the storms. Disconnecting the foundation drain from the sanitary sewer, where it is connected, takes groundwater out of the overloaded system.

The City of Markham has offered subsidy programs for backwater valve installation and related basement flood protection at eligible homes, with conditions that the work be done by a licensed plumber under a City permit. The programs change; read the City’s current page before signing a quote, and ask the plumber to quote the valve and the pump separately so you can see what each protects against.

• City’s current subsidy program checked for eligibility
• Licensed plumber and City plumbing permit number
• Camera inspection recording and locate
• Sump pump tested and battery backup quoted
• Grading and downspouts checked around the foundation

Who owns which pipe

In Markham the owner is responsible for the sewer lateral on private property up to the property line, and the City for the section from the property line to the main; York Region operates the trunk sewers and water supply behind that. A camera inspection with a locate tells you which side a break or blockage is on. If it is the City’s side, contact the City; if it is yours, the repair is yours. Keep the recording; an insurer will want it for a sewer backup claim.

Sewer backup and overland water are usually separate add-ons on an Ontario home policy, and insurers commonly ask whether a backwater valve is installed. Check both before the next storm.

Before the next storm

Lift the sump float and listen for the pump; if it has never run, have a plumber test it under load and fit a battery backup. Extend downspouts well away from the foundation and correct settled grading so water runs toward the street. Keep valuables off the basement floor and photograph the basement now, before you need to prove what was there.

If the house is in a Tarion new-home warranty period, a basement leak through the foundation may be a warranty claim rather than a repair bill; report it to the builder and Tarion in writing within the warranty timelines.