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Slopes & Ramps

Slopes & Ramps

Slopes & Ramps

Technical

Pitch

PITCH is the ratio of RISE to RUN.  Pitch is also considered the slope RATIO.

  • Rise is given first, and then run.
    • Note this is different from (X, Y) coordinates, in which you give the “X” value before “Y”. For cartesian coordinates, you ‘run before you jump’.
  • Both rise and run need to be in the same units. Typically the run is given in 12 (inches per foot).
  • Even if the slope fraction can be reduced, it’s sometimes still given out of 12 as a reference point for the value.
  • 5:12 = 5 inches rise to 12 inches run.

Slope can also be given in percentages. To calculate slope %, take the rise and divide by the run. Then multiply by 100%

  • 5:15 = 5 divided by 15 = .3333 x 100% = 33.3% slope
  • 5:10 = 5 divided by 10 = .5000 x 100% = 50.0% slope

Note: Finished surfaces should always have positive drainage and be free of undrained depressions since these may cause water stagnation. Using a minimum slope of 1.5% allows for deviations or construction tolerance that may result in the slope being less than designed.

Slope Chart

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

Rules of Thumb

  • 2-3% can be used for calculating the slope of parking lots.
    • Quick calculations: across a 62’-0” double loaded parking aisle should have a grade change of 1’-0” minimum and max of 3’-0”
  • Interchanges (roads)
    • Up-Ramps to interchanges 3-6%
    • Down Ramps from interchanges 8%
  • 2.0 to 10% – Drainage ditches
  • 0.5 to 1.5% – Sanitary sewers (depending on diameter)
  • 2.0 to 3.0% – Grassy areas for recreation
  • 1.5 to 5.0% – Paved parking areas
  • 0.5 to 10.0% – Roads

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