Ask the Builder
Installing Downspout Drain Lines
By Tim Carter
©1993-2008 Tim Carter
Summary: Installing drainage systems with downspout drain lines is simple enough to do. First check with your local government. Stormwater rules and regulations may prohibit some of your ideas. Can you discharge rainwater onto your property? Drainage systems that use a smooth 4 inch diameter plastic SDR-35 pipe will have few problems. Read my tips for better drainage.
Related Articles: drain tile, storm water drainage, foundation drainage
DEAR TIM: I need to bury downspout drainage pipes in my yard before the yard is seeded. Where is the best place to put them and how deep should they be buried? What type of pipe do you like? How far away from the house should the pipes extend? A friend suggested using pop-up valves to help water the lawn and plants. Are those a good idea? Rich T., Jackson, MS
DEAR RICH: Stormwater drainage from roofs is a topic sometimes ignored by builders and homeowners alike. I can't tell you how many houses I see where the downspouts empty onto a splash block at the base of the foundation. Often these homeowners are plagued with water seepage into basements or crawlspaces and it's no wonder. A heavy rainfall on an average sized roof can produce hundreds and thousands of gallons of water that spew from the different downspouts located around the house.
Before you proceed with any work, you should check with your local government to see if they have special stormwater rules and regulations. Sometimes you have to pipe this water to special underground storm sewers or above ground channels. Some local governments or agencies have no rules or regulations.
I usually dig a trench about 12 to 14 inches deep for downspout drain lines. If the lot is fairly flat, the pipes will get deeper the farther they extend as you should create 1/8 inch of fall for every foot the pipes run. The pipes should never be buried in the non-compacted fill dirt that is placed against the foundation. Over time this dirt or soil settles and it can cause piping to break, kink or develop reverse, or backwards, slope. Downspout piping can cross the uncompacted fill at a 90 degree angle so that it is placed in undisturbed soil. But as the soil adjacent to the house settles over time, this small length of piping needs to be checked and lifted to ensure it drains.
Smooth 4 inch diameter plastic SDR-35 sewer pipe is the material I prefer to use. This pipe has a smooth interior and closely resembles the thick-walled plastic piping used for interior house drain and vent piping. Fittings can be permanently welded to the pipe with PVC cement or you can buy rubber gasketed fittings that require no glue. If you install either type as directed, tree roots that create clog nightmares will never be able to enter the piping system. I am not a huge fan of the corrugated flexible black piping for downspouts. It can crush easily and it is nearly impossible to clean with professional drain cleaning equipment.
If you are allowed to drain your stormwater on your own lot, do so as far away from your home as possible. Try to pipe all water to a low point away from your home. Do not drain more water to a point on your lot than would have ended up there naturally before your home was built. Simply keep in mind where the water is falling on the roof and where that water would drain if your house had never been built. If you pipe the water where it used to go, you should not harm any of your surrounding neighbors.
Inline popup valves do a good job of allowing rainwater to discharge onto your property, so long as you are allowed to drain the stormwater on your property. Try to strategically place them where they will do the most good for your vegetation.
An invaluable tool that will come in handy in future years is a collection of photos that are shot as the downspout piping is being installed. If you stand back and include parts of the house in the photos and place shovels or other objects in the photos for scale, these prints will help you locate the pipes in the future. Over time it is very easy to forget where hidden pipes pass in the ground.
My own photos saved me a ton of work just last year. I had to install a small field drain in a side yard. The photos I had taken 17 years before allowed me to locate within five minutes the drain pipe to which the new drain was to be connected. I could have dug for an hour and missed the pipe by inches without the aid of the photographs.
