Grading and Drainage Around Your House in Ontario

Your basement flooded last spring. Or you've got water pooling against your foundation every time it rains. Or your deck footings are sitting in a puddle. All of these point to the same problem: poor grading and drainage around your house.

In Ontario, where we get freeze-thaw cycles, heavy spring runoff, and clay soil that doesn't drain well, proper grading isn't optional. It's the difference between a dry basement and $10,000+ in foundation repairs.

This guide covers how grading and drainage work, what Ontario Building Code requires, how to fix common problems, and what it costs in 2026.

What is Grading and Why It Matters

Grading is the slope of the ground around your house. Done right, it directs water away from your foundation. Done wrong, water flows toward your house, pools against the foundation, seeps into the basement, and saturates the soil under your deck footings.

Ontario Building Code requires a minimum 5% slope (6 inches of drop over 10 feet) away from your foundation for at least the first 6 feet. Many builders aim for 6-8% to account for settling.

If your lot is flat or slopes toward the house, you need to regrade or install drainage systems to move water away.

What Happens When Grading Fails

• Basement flooding — water enters through cracks, window wells, or porous concrete
• Foundation damage — hydrostatic pressure pushes against foundation walls, causing cracks and bowing
• Deck footing failure — saturated soil loses bearing capacity; footings settle or shift
• Mold and rot — moisture under decks, against siding, or in crawlspaces creates ideal conditions
• Ice dams in winter — water freezes against the foundation, expands, and cracks concrete

Clay soil in KWC makes this worse. Clay holds water instead of draining it, so even small grading errors create big problems.

How to Check Your Grading

Walk around your house after a heavy rain. Look for:

• Puddles within 6 feet of the foundation — water should flow away, not pool
• Water stains on foundation walls — sign of regular pooling
• Settled soil — depressions near the foundation where soil has compacted
• Downspouts dumping water near the house — should extend at least 6 feet away
• Mulch or soil above foundation level — soil should slope down from the house, not up

Use a 10-foot straight board and a level. Place one end at the foundation and the other 10 feet away. Measure the gap under the board at the foundation end. You want at least 6 inches of drop (5% slope), ideally 7-8 inches (6-8%).

If the ground is level or slopes toward the house, you need to fix it.

Fixing Grading Problems

Option 1: Add Clean Fill and Regrade

For minor issues, you can add clean fill (sandy loam or topsoil) near the foundation and slope it away.

Steps:

• Remove sod and vegetation within 6 feet of the foundation
• Add clean fill, starting 2-3 inches below siding level
• Slope at 6-8% for the first 6-10 feet
• Compact every 4-6 inches with a plate tamper
• Replace sod or add erosion control (river rock, mulch, or plantings)

Cost: $500-1,500 for a typical side of a house (DIY with rented equipment) or $1,500-4,000 for professional grading and compaction.

Watch out for:

• Don't pile soil above your siding or brick weep holes
• Don't bury deck joists or rim boards — maintain at least 6 inches of clearance
• Clay-heavy fill won't drain; use sandy loam or engineered fill

Option 2: Install French Drains

If regrading alone won't work (tight lot, steep slope toward the house, or high water table), install a French drain — a perforated pipe buried in gravel that collects and redirects water.

Two types:

1. Exterior foundation drain — runs along the footing, collects water before it reaches the foundation. Required by OBC for new builds but often missing or failed in older homes.

2. Surface French drain — shallow trench 1-2 feet deep that intercepts surface water before it reaches the house.

Cost:

• Surface French drain: $1,500-3,500 for 50 linear feet (3-4 feet deep, gravel, perforated pipe, filter fabric)
• Exterior foundation drain (excavate and install): $8,000-15,000 depending on depth, access, and whether you waterproof the foundation at the same time

French drains need an outlet — a storm sewer connection, daylighting to a lower part of the yard, or a sump pit. In KWC, you generally cannot discharge to the street or neighbor's property without permission.

Option 3: Extend Downspouts

If water is pooling because downspouts dump next to the foundation, extend them.

Options:

• Rigid extensions — 6-10 feet of solid pipe or channel, buried or surface-mounted
• Flexible extensions — corrugated tubing, cheap but visible
• Buried discharge — pipe runs underground to daylight 15-20 feet away or connects to a dry well

Cost: $50-150 per downspout for DIY extensions; $300-800 per downspout for buried drainage professionally installed.

Always slope buried downspout lines at least 1% to prevent freezing and backups.

Option 4: Install a Dry Well or Rain Garden

If you can't daylight water or connect to storm drains, collect it in a dry well (gravel-filled pit that slowly percolates water into the soil) or a rain garden (planted depression that holds water temporarily).

Dry well cost: $800-2,000 for a 4-6 foot diameter well, 4-6 feet deep, lined with filter fabric and filled with clean stone.

Rain garden cost: $500-1,500 for excavation, amended soil, and native plantings.

Both work better in sandy or loamy soil. In heavy clay, they fill up and overflow quickly — you may need an overflow outlet or underdrains.

Grading and Your Deck

If you're building or repairing a deck, grading matters twice as much.

Deck footings need stable, dry soil. Saturated soil loses bearing capacity. When footings settle or shift, your deck sags, joists crack, and ledger boards pull away from the house.

Ontario Building Code requires deck footings to bear on undisturbed soil or engineered fill at or below the frost line (minimum 4 feet deep in KWC). If you're regrading, don't add fill around existing footings without consulting an engineer — it changes the load profile and can cause settlement.

Under-deck drainage: If you have an elevated deck, water still needs to flow away from the house underneath it. Slope the ground at 2-3% minimum. If you're adding deck drainage systems, you still need proper base grading.

Ledger board protection: Poor grading that directs water against the house also soaks the ledger board. Use ledger flashing and ensure the grade slopes away from the ledger. Check for ledger rot annually if you've had grading issues.

If you're planning a deck project in KWC, proper site grading should be part of your deck quote and addressed before footings are dug.

Grading and Patio Drainage

Concrete, interlock, and stone patios also depend on good drainage.

Patios should slope 1-2% away from the house (1-2 inches of drop over 10 feet). Less than that and water pools on the surface. More than 3% and furniture tips.

If you're installing a patio on poorly graded soil, you'll need to:

• Excavate and install a compacted gravel base (4-6 inches for interlock, 6-8 inches for concrete)
• Slope the base and the finished surface away from the house
• Add edge drains or weeping tile at the low side if the patio abuts a retaining wall or sits in a low spot

For concrete patios, slope the slab itself. For interlock, slope the base and set pavers level on the slope. For natural stone, slope the base and use a sand or polymeric sand setting bed.

Cost impact: Regrading and adding proper drainage base adds $2-5 per square foot to patio installation costs. Skipping it means standing water, frost heave, and eventual settling.

What About Retaining Walls?

If your lot slopes toward the house and you can't regrade without a retaining wall, you're looking at $50-150 per square foot of wall face for engineered block or poured concrete, plus drainage behind the wall (weeping tile, gravel backfill, and drainage outlets).

Retaining walls over 4 feet tall typically require an engineer's stamp and a building permit in KWC. Even shorter walls need proper drainage or they'll fail within 5-10 years.

Permits and Code

Regrading: Generally does not require a permit unless you're changing drainage patterns that affect neighboring properties, adding retaining walls over 4 feet, or altering municipally-owned drainage infrastructure.

French drains and drainage alterations: No permit required for on-site drainage improvements, but you cannot discharge onto the street, sidewalk, or neighboring property without permission. Some municipalities require a sump pump discharge permit if you're connecting to storm sewers.

Deck and patio drainage: Addressed as part of deck and patio permits (if required). Inspectors will check that site grading directs water away from footings and the house.

If you're unsure whether your drainage work needs approval, contact your municipal building department (Kitchener, Waterloo, or Cambridge) or the Grand River Conservation Authority if you're near a floodplain or watercourse.

DIY vs. Hiring a Pro

DIY grading works if you're adding 2-4 inches of fill over a small area, extending downspouts, or installing simple surface drains. Rent a plate tamper ($80-120/day) and buy clean fill from a landscape supplier ($30-50/yard delivered).

Hire a contractor if you need:

• Excavation deeper than 2 feet (risk of utility strikes, need for shoring, or large equipment)
• French drains that tie into footings or require sump pump installation
• Grading that affects deck footings, retaining walls, or neighboring properties
• Machine grading and compaction over large areas

Cost for professional regrading: $2,000-6,000 for a typical house perimeter, depending on access, amount of fill, and whether you need drainage systems installed at the same time.

Get quotes from foundation repair companies, landscaping contractors, or excavation specialists. Make sure they understand Ontario frost depth, clay soil compaction, and OBC drainage requirements.

Common Questions

How much slope do I need around my house in Ontario?

Ontario Building Code requires minimum 5% slope (6 inches of drop over 10 feet) for the first 6 feet from the foundation. Many builders use 6-8% to account for settling. Beyond 6 feet, you can transition to a gentler slope or level grade as long as water continues to flow away from the house.

Can I regrade around my deck without disturbing the footings?

Yes, but carefully. Don't add fill directly against footings unless it's compacted and well-drained — loose fill can settle and shift the footing. Maintain the original grade at the footing and slope away from it. If you need to raise the grade significantly, consult a structural engineer to confirm the footing depth and bearing capacity remain adequate.

What's the best soil for grading around a house?

Sandy loam or engineered fill with good drainage. Avoid pure clay (holds water) and organic topsoil (settles too much). In KWC's clay-heavy soil, you often need to bring in 50-70% sand content fill to ensure water drains away from the foundation instead of pooling.

How do I stop water from pooling under my deck?

Slope the ground under your deck at 2-3% minimum away from the house. If the deck is elevated and you can't access the soil easily, consider installing an under-deck drainage system that channels water away. For ground-level decks, proper grading before deck installation is critical.

Do I need a permit to regrade my yard in Kitchener, Waterloo, or Cambridge?

Generally no, unless you're altering municipal drainage infrastructure, building a retaining wall over 4 feet tall, or changing drainage in a way that affects neighboring properties. If your lot is in a flood zone or near a watercourse, check with the Grand River Conservation Authority before making changes.