Lot Grading in London, Ontario: Rules, Slopes and Fixing Water That Runs Toward Your House
Lot grading is the shape of the ground around your home, and it decides where every drop of rain and snowmelt goes. Get it right and water flows away from your foundation into swales, catch basins or the street. Get it wrong and you get wet basements, cracked patios, soggy lawns and disputes with the neighbours.
Here's what London, Ontario homeowners need to know about lot grading: the rules, the slopes, the warning signs, and how a yard is regraded properly.
Why lot grading matters
Protects your foundation. Water sitting against basement walls is the number one cause of leaks and damp basements.
Prevents ice in winter. Poor grading creates icy patches on walkways and driveways after every thaw.
Keeps lawns healthy. Grass drowns in low spots and dies off in summer on high spots.
Keeps the peace. Changing how water leaves your lot can flood the house next door.
How lot grading works in London subdivisions
When a subdivision is designed, each lot gets an engineered grading plan. Newer London neighbourhoods use swales and catch basins to direct water away from homes, and the City's pool fence page warns that building without considering overland flow or your lot grading plan can lead to costly re-engineering.
Under London's Drainage By-law WM-4, many properties have to post a lot grading security before a building permit is issued, which is released after a final lot grading certificate confirms the grading matches the certified plan (section 5.13).
After you move in, maintaining positive drainage becomes your job. Many Ontario municipalities, such as King Township, say it plainly: homeowners are responsible for keeping water flowing away from the foundation and for correcting any changes they make that alter surface flow.
Target slopes: what "good grading" looks like
Away from the house: a common rule of thumb is about 6 inches of drop over the first 10 feet, roughly 5 percent.
Side yards and swales: enough fall to keep water moving. Toronto's infill grading guidelines, for example, call for side-yard surface slopes and swales of at least 1.5 percent.
Slopes you can mow: steep banks are hard to maintain and erode. Toronto's guideline caps swale side slopes at 33 percent.
Your own lot grading plan, if you have one, sets the specific elevations for your property.
Signs your lot grading needs work
Water pooling within a few feet of your foundation after rain
Damp basement walls, efflorescence or musty smells
Soil that has settled into a trench along the foundation
Patios or walkways that tilt toward the house
Ice forming in the same spots every winter
Washouts, erosion channels or exposed tree roots
A swale that's been filled by gardens, sheds or fences
How SPM regrades a yard
Assess. We check existing elevations with a laser level, look for swales and outlets, and review your lot grading plan if available.
Locate utilities. Free locates are requested through Ontario One Call before any digging.
Strip sod and topsoil from the work area and stockpile reusable topsoil.
Cut and fill the subgrade with compact equipment to create positive slope away from the house.
Add drainage where grading alone won't do it, such as French drains, catch basins or downspout extensions.
Topsoil and sod. We finish with quality topsoil and fresh sod, so the yard is usable right away.
Common grading mistakes to avoid
Raising garden beds against the foundation. Mulch and soil piled above the siding line trap water against the wall.
Fences or sheds across a swale. They act like dams.
Filling low spots without fixing the slope. The water just moves.
Pointing downspouts at the neighbours. London's WM-4 prohibits directing downspouts toward a side yard in a way that damages adjoining property.
Grading in wet clay. Working saturated clay smears and compacts it. Timing matters.
Lot grading for new builds, additions and pools
If you're building a home, addition, garage or pool, grading is part of the plan from day one. Inground pools in London need a grading and drainage plan as part of the pool fence permit application. Our excavation checklist for homeowners and builders covers the rest of the site prep.
Frequently asked questions
How much should the ground slope away from my house?
About 6 inches over the first 10 feet is a common target, then a gentler slope toward a swale or outlet.
Can I change the grading of my yard?
Yes, as long as you don't change how water flows onto neighbouring lots. Check your lot grading plan first in newer subdivisions.
When is the best time to regrade?
Late spring through fall, when soil isn't saturated or frozen. Fall regrading lets you sod and get roots established before winter.
Do you work outside London?
Yes. We serve St. Thomas, Strathroy, Komoka, Ilderton, Dorchester and the wider Southwestern Ontario region.
Book a lot grading assessment
SPM Landscape & Excavation has been grading and draining properties across Southwestern Ontario since 2006. We're WSIB covered with $1M liability insurance. Call or text (519) 474-0008 for a free quote.
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