Grating Grading

Grading … it’s one of my pet peeves. Landscapers/developers should know better, but they don’t always get grading right. Or they forget to check for it, or it was done (sort of) but with time, erosion and settling, the grading changed.

To emphasize the seriousness of grading, my landscape design instructor told the class about a landscape grading error he made early in his career. The landscape drawings had the proper grading, but during construction the heavy machinery had changed the grade. The landscape architect didn’t check the final landscape. The house flooded. The owners sued the landscape architect. End of story.

I can’t sue anyone for the terrible landscape grading around my house. When I bought my house a couple of years ago, it was already 12 years old. The landscape had been inspected by city engineers on completion and five years later (to take the lanscape settling into account). No one reported the bad landscape grading.

At the back, the patio had a downward slope into the house.

At the side of the house, the main downspout had eroded the path down to the subsoil

The neighbours downspout poured directly onto our pathway to the driveway. Since the soil was clay, puddles would collect at the path/driveway interface. Water percolated through the pathway and under the asphalt, which caused frost heave damage along the driveway.

The back lawn had soggy wet areas and the front lawn had areas where water collected after a shower.

With time and money, the drainage issues have been addressed one by one. But even the professional landscapers we hired introduced new drainage issues. Luckily we caught them in time and had them corrected. No, I am not getting into how they created the problems. They should have known better…they were smart, experienced landscapers.

Just so this isn’t just a whinge session, I’m giving you general information that will help you with landscape grading. Residential Landscape Architecture by Norman K. Booth and James E. Hiss (fifth edition), cites 4 places where “special effort should be made to correctly drain surface water.”

Surface water should:

1. Drain away from the house. The ground’s surface needs to slope away from the house at a rate of 1 to 10 percent.

A slope of 1 percent rises or falls 1 foot for every 100 horizontal feet (1 divided by 100 = 0.01 or 1 percent). Whereas a slope of 10 percent rises or falls 10 feet for every 100 horizontal feet.

2. Drain as quickly as possible from paved walks and driveways. Recommended minimum slopes:

Concrete and asphalt 1 percent

Exposed aggregate concrete, brick, stone or other rough pavement material 1.5 percent

Don’t go overboard with slopes.

Paved places where people congregate shouldn’t exceed 3 percent…more than this gives the space an uncomfortable and unstable feeling.

Paved walks should not exceed 5 percent slope

Driveways and parking should nor exceed 8 percent.

3. Drain from lawn surfaces to prevent standing water or soggy wet areas. Recommended slope, 2 percent.

4. Drain from planting beds. Slope: at least 2 percent but no more than 10 percent. Steeper slopes are subject to erosion.

 

This is what I did on my property (with the proper grading and recommended slopes) in the last 3 years:

At the back, the new patio drains water away from the house

Tile drainage at the back and the side of the backyard drained water off the property to a large grassy swale

The front pathway has a 2 percent slope that allows rapid transport of water.

The water from the neighbour’s downspout flows into a pipe, which directs the water to a swale on the side of the property.

 

The damaged asphalt driveway still needs to be addressed. I am thinking of putting in a permeable driveway. More expensive, but will last longer than asphalt.

 

Grading isn’t a luxury in the landscape; it’s a necessity.


Written by Cristina da Silva
Monday, October 17, 2011 in Soil in Landscaping

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