Enter the drop and the distance it happens over.
Guidance only. Your lot's approved grading plan and the Ontario Building Code's site-grading rule (keep water from collecting against the building) set the real requirements.
How to measure the slope of a yard
Tie a string to a stake at the house wall, run it out 10 ft to a second stake, and level it with a line level. The distance from the string down to the ground at the far stake is the drop. Enter both numbers. A long straight board with a spirit level works the same way over a shorter run. Measure in two or three places, because yards rarely fall evenly.
Reading the result
| Slope | What it usually means |
|---|---|
| Falls toward the house | Water runs to the foundation. Fix this first. |
| Under 1% | Too flat; water tends to sit and soak in near the house. |
| 1–2% | Drains slowly; puddles after heavy rain are common. |
| 2% or more | Drains. Paved surfaces we build fall at least 2% (about ¼ in per foot). |
| Over about 33% (1:3) | Hard to mow and prone to erosion; terraces or a wall may suit it. |
The Ontario Building Code asks that a building site be graded so water doesn't collect against the building. It doesn't give a single number for every yard, and many subdivisions have an approved grading plan that does. If you have one, it wins over any rule of thumb.
Fixing a yard that slopes the wrong way
Most fixes start at the house: build the grade back up with compacted fill and topsoil so it falls away, extend downspouts, and give the water a legal place to go, such as a swale, the street side or a lower part of your own lot, never a neighbour's. Where the yard drops steeply, short retaining walls turn one slope into level terraces. See drainage and grading and retaining walls; our typical GTA range for a grading and drainage fix is $3,500–$9,000.
Percent, ratio and degrees
Percent grade is the drop divided by the distance, times 100. A 6 inch drop over 10 ft is 5%. The same slope is a ratio of 1:20 and an angle of about 2.9 degrees. Builders and grading plans usually use percent; walls and embankments are often described as ratios.
Questions about this tool
How do I calculate the slope of my yard?
Divide the drop by the distance, in the same units, and multiply by 100. A 6 inch drop over 10 ft (120 inches) is 6 ÷ 120 × 100 = 5%. Measure with a string, two stakes and a line level, starting at the house wall, and check two or three spots.
How much should my yard slope away from the house?
Enough that water runs away rather than sitting: paved surfaces we build fall at least 2%, about a quarter inch per foot. The Ontario Building Code asks that water not collect against the building, and your subdivision's approved grading plan, if you have one, sets the exact numbers for your lot.
What does a 2% slope mean?
The ground drops 2 units for every 100 units of distance: about a quarter inch per foot, or 2 cm per metre. Over 10 ft that is about 2.4 inches. It is a common minimum for paved surfaces to shed water, and it is barely visible to the eye.
When does a slope need a retaining wall?
When it is too steep to mow or keeps washing out, roughly steeper than 1:3, or when you want level space for a lawn or seating. Short terraced walls drain more easily than one tall wall, and walls over 1 m of exposed height near public areas need a permit and engineer.
Sources
- Ontario Building Code, O. Reg. 332/12 (site grading, 9.14.6)
- Country Reno: interlock driveway installation in Toronto (base depths, ICPI guidance)