Natural Surface Method
This method means to literally cut slopes next to the house
for the water to run away on the surface of the ground. When we talk about
cutting dirt away from the house, we typically like to have the elevation of the
dirt sloping away at about 5% for at least 5 to 6 feet. No standing water should be next to the house at
any time. Not even in a heavy rain. Having water soak through the soil down to
the bottom of our footings is always a bad idea. Getting water down that low
can cause swelling and shrinking of the soil, which in turn can crack foundations.
An advantage of this method is the ability to create
beautiful landscape features based around drainage. I was working on a lot where
there was a particular tree the owner wanted to keep. The tree was quite close
to where they wanted the front door and up a bit of a knoll. The question
became, “What do we need to do to maintain the integrity of the tree and its’
root system while also accommodating the elevation needs of the home?” The
owner wanted the finished floor as low as possible to the soil grade. The
solution was putting a retaining wall around one side of the tree. Then I put a
dry river bed between the retaining wall and the house which carried the water
around to the back yard. The home owners
added a wooden bridge over the river as an entrance to their wrap around porch.
Then they added plants along the river’s edge to make it look more natural. Having
the topographical map on this job was a great benefit.
Catch Basis/Pipe Method
The advantage of this method is you can run the grades out
of a catch basin through a pipe flatter than you can on a natural surface. For example, a 6-inch storm drain pipe can easily
run on a 0.5% grade which is really flat.
Most contractors run water over concrete driveways and sidewalks at a 1%
grade. Typically, asphalt will be laid at a 2% slope for proper water run-off. Another
consideration if using this method is the volume of water that the system needs
Another consideration is the type of pipe that you are
using. For example, if using corrugated black ABS pipe, flatter grades are more
difficult compared to a PVC pipe. The reason is, PVC pipes are made of hard
plastic and do not have any ridges; therefore, are flatter and not flexible. They
will hold truer to the grade. One must keep the pipe running plane. Or in other
words, shouldn’t have the pipe running up and down and up and down. On the
other hand, the ridges in an ABS flexible pipe are easier to use. The down side is all those little ripples/ridges
will fill with sediment quickly.