Grading

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Theta.jpg

Slope gradient

Slope gradients are expressed as Y:X where Y is a single unit of rise and X is the corresponding run. It can be calculated by dividing the rise by the run: e.g.:

Slope percentage

Slope percentage is calculated similarly by dividing rise by run, but then multiplying by 100 to get a percentage: e.g.:

Slope in degrees

Expressing a slope in degrees requires using the inverse tangent trigonometric function. e.g.:

[1]

Grading Standards and Critical Gradients[2]
Use Extreme range (%) Desirable range (%)
Public Streets 0.5 - 10 1 - 8
Private streets 0.5 - 20 1 - 12
Service lanes 0.5 - 15 1 - 10
Parking areas 0.5 - 8 1 - 5
Parking ramps up to 20 up to 15
Collector walks 0.5 - 12 1 - 8
Entrance walks 0.5 - 8 1 - 4
Pedestrian ramps up to 12 up to 8
Stairs 25 - 50 33 - 50
Game courts 0.5 - 2 0.5 - 1.5
Paved gutters 0.25 - 100 1 - 50
Grassed swales 0.5 - 15 2 - 10
Terraces and sitting areas 0.5 - 3 1 - 2
Grassed banks up to 50 up to 33
Planted banks up to 100 up to 50
  1. Ontario. O. Reg. 191/11: INTEGRATED ACCESSIBILITY STANDARDS, 2011. https://www.ontario.ca/laws/regulation/r11191.
  2. Strom, S., Nathan, K., Woland, J. Site Engineering for Landscape Architects (6th Ed.) 2013, Wiley and Sons