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Expressing Slopes or Gradients

Discussion in 'Landscape Architecture and Design' started by longslawn, Feb 1, 2002.

  1. longslawn

    longslawn LawnSite Member
    Posts: 201

    I'm studying for Landscape Contractors License and have a question that I need to be sure I understand. According to the manuals a ratio of :
    100:1 1' of rise per 100' of run or 1%

    Are these correct below

    50:1 1' of rise per 50' of run or 2%
    33:1 1' of rise per 33' of run or 3%
    20:1 1' of rise per 20' of run or 5%
    10:1 1' of rise per 10' of run or 10%
    5:1 1' of rise per 5' of run or 20%
    4:1 1' of rise per 4' of run or 25%
    2:1 1' of rise per 2' of run or 50%

    1:1 1'' of rise per 1'of run (this is the on throwing me)

    I thought 1:1 would be 1'of rise per 1' of run?

    Am I missing something or is there an error on the inch mark in the manual.
    Thanks
     
  2. diginahole

    diginahole LawnSite Member
    Posts: 249

    Your math is correct, however I believe you may have your ratios reversed. 1:50 rise:run ratio = 2% grade. Mathematically speaking, the : is equivalent to a division sign.

    1:1 ratio = 100%
    1:12 (inch per foot) = 8%
     
  3. longslawn

    longslawn LawnSite Member
    Posts: 201

    The manual list the ratios like I listed them (ie 50:1) The horizontal distance is always first with the vertical distance last.
    The question I have is, in the book a 1:1 ratio 1 inch of vertical rise for every foot of distance isn't correct is it? Thats what the book states.
    In the case of 1:1 being 100% wouldn't it be 1 foot of distance and 1 foot of rise?
    Thanks for the reply. Hope i'm asking the question correctly.
    Thanks
     
  4. diginahole

    diginahole LawnSite Member
    Posts: 249

    If your book states it as a run to rise as opposed to a rise to run I would go with that then.....seems wrong to me but I have been wrong many times before. I know for sure that a inch every four feet (close to 50 inches) is the same as a 2% grade.

    A 1 to 1 ratio signifies that all things are equal (ie: 1 foot per foot or 1 inch per inch or 1 anything per 1 same thing.) To express a 1 inch rise per one foot of run we need to work in a common unit. To express it as a run to rise ratio it would be stated 12:1. However it would be valid to state it as 1':1" so long as both units are shown.

    Clear like mud???
     
  5. digger242j

    digger242j LawnSite Member
    Posts: 14

    In earthmoving I've always seen it expressed in run to rise--a 2:1 slope, a 4:1 slope, etc. If it helps to visualize it this way, a 1:1 slope is equal to a 45 degree angle. 2:1 would be 22 1/2 degrees.

    We get plans for sewers with the slope expressed in percentages. 1% is 1 foot of fall in 100 feet of length. 2% would be 2 feet of fall in 100 feet. Pipe laying lasers are adjusted in percentage. Just dial in the specified percent of slope and follow the beam.

    That would be the same as 1/4" per foot. 1/8" per foot is pretty close to 1%, but not exactly. There are 96 eigths of an inch in a foot. Pretty close to 100, so it works out ok.

    I think the 1" of rise per 1' of run must be a typo
     
  6. longslawn

    longslawn LawnSite Member
    Posts: 201

    Thanks for the replys. I think it is a typo error also. Just wanted to get another opinion to check.
    Thanks
     

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