Why Is My Backyard Flooding? Yard Drainage Fixes for London, Ontario's Clay Soil
If your backyard turns into a pond every time it rains, you're not alone. Soggy lawns, standing water against the foundation and muddy low spots are among the most common calls we get in London, Ontario. The good news: almost every yard drainage problem has a fix, and most of them start with understanding where the water comes from and where it's trying to go.
This guide covers the main causes of backyard flooding in London and Middlesex County, the local rules you need to know, and the drainage solutions we install most often.
Why London yards hold water: the clay problem
Much of the London area sits on heavy clay and silty soils. Clay is great at holding nutrients but terrible at moving water. When rain falls faster than clay can absorb it, water runs across the surface until it finds a low spot, and that low spot is often your yard, your patio or the side of your house.
Add compaction from construction equipment on newer lots, thin topsoil over clay subsoil, and summer storms that drop a lot of rain in a short time, and you have the perfect recipe for pooling.
The 6 most common causes of backyard flooding
Negative grading. The ground slopes toward the house or toward a hollow instead of away from it.
Short or disconnected downspouts. Roof water is dumped right next to the foundation.
Blocked or flattened swales. The shallow channel between lots that's supposed to carry water to the street or a catch basin has been filled in by gardens, sheds or fences.
Compacted soil. Heavy equipment or years of foot traffic squeeze out the pore space water needs.
Sump pump discharge that empties onto the lawn and soaks the same area all season.
A high water table in low-lying areas or near creeks.
London's drainage rules every homeowner should know
The City of London's Drainage By-law WM-4 sets clear rules that affect how you can manage water on your property:
Downspouts must discharge at least 0.7 metres from your exterior walls (section 5.12).
Downspouts can't be aimed at a side yard in a way that damages or affects the neighbouring property (section 5.10).
Downspouts can't be connected to foundation drains (section 5.11).
Sump pump discharge to the ground surface can't create continually wet ground or affect sidewalks, roads or neighbouring properties (section 5.7).
Storm water can't be discharged into the sanitary sewer (section 4.1).
If you've had water in your basement, the City also runs a Basement Flooding Grant Program that helps with eligible protection measures such as backwater valves and weeping tile disconnection with a new sump pump.
Yard drainage solutions that actually work
Downspout extensions and redirection
The cheapest fix and often the most effective. Extending downspouts well past the 0.7 m minimum and pointing them toward a swale or a part of the yard that drains can solve a surprising number of wet-foundation problems.
Regrading
If the ground around your house is flat or slopes inward, regrading is the long-term fix. We remove sod, cut and fill to create positive slope away from the foundation, add topsoil and re-sod. Our guide to lot grading in London explains the slopes we aim for.
French drains
A French drain is a perforated pipe in a trench of clean stone wrapped in filter fabric. It collects water from saturated soil along its length and carries it away. In clay soil, the key is the outlet: a French drain that has nowhere to discharge just becomes an underground puddle. We design every drain line with a proper fall and an outlet such as a swale, a dry well or an approved storm connection.
Catch basins and surface drains
For low spots, patios and the bottom of slopes, a catch basin collects surface water through a grate and pipes it away. Catch basins pair well with French drains when you have both surface runoff and saturated soil.
Swale restoration
Many newer London subdivisions rely on rear-yard and side-yard swales and catch basins designed into the lot grading plan. If yours has been flattened by landscaping or a fence, restoring it can bring back the drainage the subdivision engineer intended.
Dry wells
Where there's no good surface outlet, a dry well can store and slowly release water into the ground. In clay these need careful sizing; under WM-4, a dry well used for foundation drain flows must be designed and certified by a professional engineer.
What not to do
Don't just pile topsoil on low spots without fixing the slope. Water will find a new low spot.
Don't redirect your problem into your neighbour's yard. It's against the by-law and it starts disputes.
Don't connect downspouts to your weeping tile.
Don't skip locates. Always request free utility locates through Ontario One Call before digging.
How SPM tackles a drainage problem
We visit during or after rain if possible to see where water collects.
We check grades with a level and look at downspouts, swales and sump discharge.
We recommend the simplest fix that will work, from extensions to regrading to full drain systems.
We excavate, install, backfill, regrade and re-sod so your yard looks better than before.
Frequently asked questions
Do French drains work in clay soil?
Yes, if they're built for it: correct slope, clean stone, filter fabric and a real outlet.
How far should downspouts discharge in London?
At least 0.7 metres from the exterior wall under the City's Drainage By-law, and never toward a neighbour in a way that causes damage.
How much does yard drainage cost?
It ranges from a few downspout extensions to a full regrade with drain lines. We give free quotes after seeing the site.
Is fall a good time to fix drainage?
Yes. Fixing drainage before freeze-up prevents ice buildup and spring flooding. See our fall yard prep checklist.
Get your yard drainage fixed
SPM Landscape & Excavation has been solving drainage problems in London, St. Thomas, Strathroy, Komoka, Ilderton and Dorchester since 2006. Call or text (519) 474-0008 for a free assessment.
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