Vancouver Island gets a lot of rain. Here's how to tell if your drainage system is keeping up.
Perimeter drains — also called weeping tile or French drains — sit around the base of your foundation and carry groundwater away from your home. They're buried underground, out of sight, and most homeowners don't think about them until something goes wrong. On Vancouver Island, where annual rainfall can exceed 1,000 mm in many communities, a functioning perimeter drain isn't optional — it's essential.
A perimeter drain is a perforated pipe installed in a trench around the outside of your foundation, typically at or below the level of the basement floor. The trench is filled with drainage gravel and wrapped in filter fabric to prevent soil from clogging the pipe. Water that collects around the foundation enters the pipe through the perforations and flows by gravity to a discharge point — usually a storm drain, ditch, or daylight outlet downhill from the house.
When the system works, water never reaches your foundation walls. When it fails, that water has nowhere to go.
This is the most obvious sign. If you're seeing standing water, damp spots on your basement floor, water stains on the lower portion of your foundation walls, or a persistent musty smell, your perimeter drain may not be doing its job. On Vancouver Island, this often shows up during the wet season (October through March) when the water table rises and rainfall is heaviest.
After a heavy rain, walk around the outside of your house. If water is pooling near the foundation rather than draining away, the perimeter drain may be blocked or collapsed. Properly functioning drainage should move water away from the foundation — not let it sit there.
Efflorescence is a white, chalky residue that appears on concrete or block foundation walls. It's caused by water moving through the concrete, dissolving mineral salts, and depositing them on the surface as it evaporates. If you're seeing this on your basement walls, water is getting to your foundation — which means your drainage isn't intercepting it.
Not all foundation cracks are caused by drainage failure, but hydrostatic pressure — the force of water pushing against your foundation — is a common cause. When a perimeter drain fails, water saturates the soil around the foundation. That saturated soil expands and puts lateral pressure on the walls. Over time, this pressure can cause cracking, bowing, or shifting. Horizontal cracks are particularly concerning as they indicate lateral pressure.
Older perimeter drains were often made with clay tile or corrugated plastic pipe that deteriorates over time. Clay tile joints separate, corrugated pipe crushes under soil weight, and decades of silt accumulation can block even well-installed systems. If your home is 30+ years old and the perimeter drain has never been replaced, there's a reasonable chance it's not performing as designed. The BC Building Code has evolved significantly since the 1990s, and modern perimeter drain installations use more durable materials and better drainage practices.
If you're seeing one or more of these signs, the first step is to have the system assessed. In some cases, a drain can be flushed or cleaned. In other cases — especially with older systems — a full replacement is the right call. A proper perimeter drain replacement involves excavating around the foundation, installing new perforated pipe with drainage gravel and filter fabric, waterproofing the foundation wall, and backfilling.
It's not a small job, but it's a lot less expensive than dealing with foundation damage, mould remediation, or a flooded basement.