Used for and examples…

%

Inch per ft

Ratio

Written

Unpaved slopes do not drain well; Slopes less than 1% should not be designed as there will inevitably be undrained depressions and water stagnation.

<1%

–

–

–

Absolute minimum slope for roof drainage; more is preferred as 1% slope can be difficult to achieve with construction tolerances.

1%

~1/8 in/ft

1:100

1 foot height change over 100 feet

Minimum recommended slope for drainage;

Minimum slope for parking areas (1.5 to 5.0)

1.5%

1.5:100

Minimum slope for drainage away from buildings (grade slope 2.0 to 50)

Maximum permissible cross slope for ADA walkway/ramp

Maximum slope for ADA parking space

2%

~1/4 in/ft

1:50

1 foot height change over 50 feet

Maximum desirable slope of a grassy (outdoor) area used for recreation (2% desirable)

3%

Walks next to building should not exceed

4%

Maximum slope for parking areas (1.5 to 5.0)

5%

1:20

1 foot height change over 20 feet

Max slope for streets used by vehicles

10%

1:10

1 foot height change over 10 feet

Max slope for automobile ramp where pedestrians are allowed

12%

1:8.33

Max slope a vehicle can climb for a sustained period of time without long term damage to the automobile.

Max for automobile ramp when pedestrians are prohibited

15%

1:6.66

20%

1:5

1 foot height change over 5 feet

Max slope for grass to stabilize the soil. Anything more and it will be hard to mow.

25%

1:4

1 foot height change over 4 feet

In order to help stabilize soil, plant ground cover that won’t need to be mowed. This slope only works if the soil is stable.

25%-50%

–

For slopes over 50%; check dams or retaining walls should be introduced to control & reduce soil erosion. Avoid slopes of 50% or greater due to erosion from water runoff. Slopes of this grade are very steep and not suitable for any kind of non-specialized activity. (grade slope 2.0 to 50)

50%

1:2

1 foot height change over 2 feet

This is a 45 degree slope

100%

1:1

1 foot height change over 1 foot