Understanding the terms
Positive grading explained
Short answer
Positive grading means the ground falls away from a building, so surface water travels outward instead of back toward the wall. Negative grading is the opposite and is the opposite direction of fall. The appropriate elevations and surface route depend on the site and applicable grading plan.
The word positive is doing simple work here. It refers to the direction of the slope relative to the building, not to any quality judgement. Ground that falls away is positive. Ground that falls back toward the house is negative. Ground with no meaningful fall in either direction is flat, and behaves much like negative grade once it collects any water at all.
How much fall is enough
Slope is expressed as a percentage: the vertical drop divided by the horizontal distance. The table below converts the figures you will hear into millimetres per metre, which is far easier to picture.
| Slope | Equivalent fall | Example only; not a site specification |
|---|---|---|
| 1 percent | Equivalent fall10 mm per metre | Example only; not a site specificationMathematical example: 10 mm of elevation change over 1 m. |
| 2 percent | Equivalent fall20 mm per metre | Example only; not a site specificationMathematical example: 40 mm of elevation change over 2 m. |
| 5 percent | Equivalent fall50 mm per metre | Example only; not a site specificationMathematical example: 100 mm of elevation change over 2 m. |
| 10 percent | Equivalent fall100 mm per metre | Example only; not a site specificationMathematical example: 100 mm of elevation change over 1 m. |
Measuring what you already have
Use the free yard slope calculator to convert metric or imperial measurements. Record direction as well as percentage; one segment does not establish the full drainage route. For wet lawns, see backyard drainage guidance.
Step 1: Find a straight board and a spirit level
Two metres is ideal because it matches the distance the common guideline refers to. A long level on its own works if you do not have a board.
Step 2: Rest one end against the foundation
Put the board on the ground with one end touching the wall, running straight out into the yard.
Step 3: Raise the far end until the level reads true
Lift the outer end of the board only. Keep the wall end resting on the ground.
Step 4: Measure the gap underneath the raised end
That measurement is your fall over the length of the board. Around 100 mm over 2 m puts you near the commonly recommended figure.
Step 5: Repeat on each side of the house
Grades rarely fail uniformly. It is normal to find one elevation fine and another flat or reversed.
If you have to raise the wall end instead, the ground falls toward the house. That is negative grade.
What stops you simply adding more soil
There is a hard ceiling on how much you can raise the ground against a building. Soil must stay well clear of siding, cladding and any weep holes, because burying those traps moisture against materials never intended to be in contact with the ground and creates a worse problem than the puddle you started with.
On a house where the foundation does not project far above grade, that clearance may not leave enough height to build the fall you want. In that case the answer moves outward: lower the ground further from the house, or route the water with a swale rather than trying to shed it purely by slope. That is where drainage correction comes in.
Continuity matters more than steepness
A frequent misunderstanding is that a yard needs to be uniformly sloped. It does not. It needs an unbroken downhill path from the house to the point where water leaves the property. A generous slope for two metres that then runs into a raised bed, a level patio or a fence line with soil built up against it has not solved anything, because the water reaches the obstruction and stops.
When you walk your yard, trace the whole route rather than checking the slope in one place. The failure is usually at the far end, not at the wall.
Related questions
What does 2 percent slope mean in practical terms?
Can a grade be too steep?
What if there is no room to build enough slope?
Does the grade have to be positive across the whole yard?
Next
Where to go from here
Foundation grading
What it takes to rebuild positive fall in the perimeter zone, and what limits how high you can go.
Lot grading
On newer lots the required elevations come from an approved plan rather than a general guideline.
Yard grading
When the whole yard rather than just the perimeter needs reworking to fix fall and drainage.
Final grading
The topsoil and finish pass that leaves a yard ready for sod, seed or landscaping.
Signs your yard needs regrading
Nine things to check if you suspect the fall around your house has been lost.