Two Primary Methods of Draining a Lot

When planning where to put your home on its lot, you want to know how the water will naturally run on your property. Then you can make sure the water will still be directed away from your foundation and not trapped at any point once the house, sidewalks and driveway are graded. Using a topographical map with the most elevation changes annotated is especially important since you will not have room for drainage errors.
The first thing is to plan the elevation of your finished floor and the amount of footing you will keep exposed.  A finished floor elevation on a very flat lot might need to be raised a little bit more than you think because of the need to run drainage water at a certain percent of slope. For example, if the water naturally flows to the back of the house, that is great.  Then you would need a plan for getting the rain and/or surface water from the front of the house to the back.

here are two primary ways to take care of drainage: the Natural Surface Method and the Catch Basin/Pipe Method. Chose the best method based on the amount of land you have in which to achieve your percentage of slope goals.

​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 Basin/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 to carry.
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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.