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house built into a hillThe shape of the earth. Slope, pitch, levelness, steepness.

Site design. Road design. Drainage design among others. There is so much to each of these disciplines, but this blog is just about slope.

The slope of the land is called topography and it heavily influences site design.  While there are landscape architects, site engineers, and architects, in reality, one cannot ignore the effect of the site on the building and the buildings affect on the site. So the two are always co-mingled. Elegant ramps, stairs, retaining walls, terraced acres of hills are affected by the slope and how it is addressed – sometimes it is a curse, other times a blessing (see photo).

Grading is the art and science of moving earth around to make the site work for its purpose.  The site steepness influences more than just who skis on which part of the mountain- the ability to climb the stairs, the velocity of water and vehicular navigation all rely on the steepness, called “grade” in design terms.  The grade is generally expressed in percentages. It derives from the expression rise/run or vertical height divided by horizontal distance.  For example, most handicapped ramps have an 8.33% grade meaning they are 1″ high per 12″ length (1/12=8.33). Cars in parking garages use 6.7% slope, and can seldom go up a grade exceeding 25 %. Most folks find walking uphill over a grade of 10% to be uncomfortable -better think of stairs. Class 2 hiking (rigorous) tops out at 18%. Sidewalks are generally sloped 2% away from the buildings to shed water, but we perceive the walking experience along the sidewalk as flat.

On the other hand: A baseball diamond needs a certain degree of levelness, where a ski slope – not so much.

profile of roadway

How we travel shows this, too. Did you ever notice how the tires on your car wear out on the right side first? Why? When one looks carefully at the shape of the road in profile it has a gentle slope called a crown or camber. The camber helps shed water toward the curb -which helps guide the water into drains or ditches. But it also slightly tilts the car, which puts more pressure and wears on the tires of the downhill side of your travel direction (see illustration).  Yet one says “dead level” that’s a problem too, since we rely on gravity to move the water.

Think of a retaining wall  (http://seconarchitect.com/retain-this-a-primer-to-retaining-walls/), this allows us to manipulate the grade to more level uses. but also disturbs the drainage patterns and movement patterns of the users.  Tilt the ditch too far and it carries away the earth -erosion happens-and has to be controlled.

manipulate grading

What’s your site challenge? Let’s talk. 914 980 5532. Ask for Steve.

Article by Steven Secon