Protecting your home against rainwater
This downspout diverter was hastily put in to get the roof water onto the sidewalk, where it will drain away from the house. It will later be replaced and piped underground. (Sept. 22, 2011) Credit: Tim Carter
1. A lot of water
Storms produce vast quantities of water on roofs. A ranch home with a roof area of about 2,400 square feet will generate nearly 1,500 gallons of water during a storm that dumps 1 inch of rain. That's a tremendous amount of water to concentrate around the foundation of your home. It can cause significant leakage in basements and crawl spaces.
2. The lowdown
Roof water should be piped to the lowest spot on the property, into municipal stormwater systems or, if you can afford it, into a cistern or other collection vessel so the water can be reused for gardening or other household uses.
3. The right pipe
Some homeowners have had nothing but success piping roof water underground in rigid PVC pipes. You might try using a pipe that's made for sewer line work. It comes with slip joints that don't have to be glued.
4. How deep?
These buried downspout lines don't have to be too deep in the soil. Usually they are no deeper than 16 inches, unless you have a flat lot. It's best to make sure they fall by a quarter-inch per foot of run. This provides plenty of pitch so the water readily flows.
5. Matter of degrees
You'll want to use 4-inch diameter pipe for your system. Be sure that any change of direction of the pipes while underground is done with 45-degree bends. The only place to use a 90-degree bend is at the end of the pipe where it turns up to capture the end of the metal downspout.
6. Bend separation
To make other 90-degree bends in the piping system, use two 45-degree bends and put a 1-foot piece of straight pipe between them. This spacing will really help you if you ever have to put a drain-cleaning snake down the pipe to unclog it.
7. Over the top
If you're in a bind and can't immediately bury the pipes, you can run them on top of the soil. These pipes look ugly, but they work. The trick is to get the water as far as possible from the house, always making sure it's aimed at the lowest part of your land where it would naturally drain if your house were not there. It's never a good idea to pipe water to part of your land where the water would not naturally go.
8. New-house rule
When installing downspout drain lines in the soil, never bury them immediately adjacent to your home if it was built within the past five to 10 years. The soil that's put in around the foundation is seldom compacted. It can take years for it to completely self-compact.
9. Uncompacted soil
If you install the lines in un-compacted soil, the pipes can bend, kink or develop reverse drainage where the water doesn't flow. If you use the slip joints, in worst cases, the pipes can come apart at the joints.
10. Extra slope
In new construction, always put the buried pipes in undisturbed soil. When you cross over the soil around the house, keep it to a minimum. Give this section of pipe extra slope, up to an inch per foot of run, to compensate for future soil settlement.
