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Glossary






Storm Water Drainage

By Tim Carter
©1993-2008 Tim Carter
Summary: Downspouts and gutters will collect and send out hundreds of gallons of water during a storm. Splash blocks only serve as a way to absorb and spread the energy of the falling water. Drain lines of durable 4 inch diameter plastic can capture and move the water to a better place on your lot. Read my column for more tips.

Related Articles: drain tile, downspout drain lines, drain crawl space

Just last night, I was watching the British Broadcasting Show Ground Force. The stars of the show had come to Atlanta, Georgia to renew the backyard of a home. As dawn broke on the second day of the two-day shoot, the stars of the show and the homeowner discovered that an overnight rainstorm had flooded the side yard and part of the back yard where the new pond, garden and deck were being installed. I know, you are wondering what in the world this has to do with your new home in Chicago. In one word: Everything!

For two brief seconds, the videographer showed the cause of the flooding. The downspouts from the roof terminated at the bottom of the exterior walls and the rushing water simply hit a two-foot long concrete or plastic splash block. The only purpose the diverter served was to absorb and spread out the energy of the falling water. Without the splash block, the soil around the house would quickly erode. The roof water was not being piped away from the home.

Many building codes do not mandate that rain water from a roof be piped away from the foundation. Keep in mind that building codes are different in many parts of the nation. We are getting very close to having one national building code, but even when we do, local building officials can tweak the code to match local practices and such.

Add to this the stormwater management problem many have just started to realize in the past 15 years. Do some research and you will discover that urban and suburban flooding has become a reality during the past 20 years. Part of this is because storm water systems designed many years ago simply underestimated the volume of water that is generated by hard surface house roofs, driveways, patios, parking lots, etc. I don't think that engineers 50 or 75 years ago ever dreamed a shopping mall or a subdivision with hundreds of homes might ever exist.

Modern planners and engineers deal with this storm water using sophisticated water retention systems. Roof downspout water can be piped directly to underground storm water retention basins. In some instances it can flow into open retention or detention features. The bottom line is that your new home should become a responsible member of the community. The water from your roof should be captured and redirected to a place where it does not cause a problem on your lot or the lot of a neighbor. At the very least, it should be released slowly so it does not overwhelm the natural waterways near your home.

If you are lucky enough to build in a community that requires storm water to be piped to a central location, be sure the piping on your lot is the right type and it is installed the correct way. Even if you are not required to discharge your storm water to a central location, it is still a great idea to divert it as far away from your home as possible.

I prefer to use four inch diameter plastic sewer line pipe for down spout drain lines. This piping is very durable and the joints between sections of pipe and the fittings are very tight. You can often buy fittings that have rubber seals or ones that are glued with a regular solvent glue. Using either type insures that water will not leak from the pipe and that tree roots will not enter the piping system.

The installer of the piping should avoid the use of 90-degree fittings except where the pipe terminates against the foundation wall and turns up to capture the roof downspout pipe. These tight bends when placed downstream in the piping are enormous obstacles for plumbers or drain cleaning companies. If your piping gets clogged in the future, 90-degree bends may prevent a company from extending a metal drain cleaning wire down the piping system. You can easily create a 90-degree turn by gluing two 45-degree fittings together. Two 45-degree bends create a gentle turn that the drain cleaning equipment can navigate.

The piping should not be buried in the un-compacted fill dirt alongside a foundation. This dirt settles over time and the piping can fracture or develop a negative pitch where water actually flows the wrong direction. It is better to put the pipe in the undisturbed soil that usually can be found about 4 or 5 feet away from the foundation. The buried pipe can cross this uncompacted soil to get to the virgin soil, but make sure it has plenty of pitch. I recommend one inch of fall for every two feet of run as it crosses this danger zone. Once the pipe is in good soil, it can have a pitch of 1/8 to 1/4 inch of fall per linear foot of run.

If at all possible, take photos of the installation of this system. These photos will prove invaluable years from now as they will help you locate the piping should you need to dig a hole or excavate for any reason on your property. Place the photos and negatives in a safe place such as your electrical circuit board panel. Put the photos in a sturdy labeled envelope and nail it to an open spot next to the electric panel. The circuit breaker panel board is rarely disturbed and makes a great spot to store facts about your home.






Comments

David
05 Dec 2007, 04:29
Tim:

Can roof water drains be "T-ed" into a French Drain system piping to move water away from the house after collecting it, or do the systems have to be entirely separate?

-David
AsktheBuilder
05 Dec 2007, 08:49
Dave,
They can be joined together far downstream from the house. You do not want water from the roof to flood the French Drain system. Never use a tee. Always use a wye with a 45-degree angle.
Dean
08 Dec 2007, 19:34
Tim,

I have a foundation drain from my house to the edge of my property. Can I connect a gutter downspout to this? If so, how far away does the connection need to be from the house?

Dean
AsktheBuilder
09 Dec 2007, 07:50
Dean,
You can do anything you want to..... Would I do it? No. You do not want to introduce more water into the foundation drain. Pipe the roof water separately.
Jim Nesset
29 Dec 2007, 13:56
I recently had a company put in a new sidewalk and put in 2 draintiles ( plastic tubing)under the new sidewalk. Previously I had two gutter extensions that drained onto the old sidewalk. They ran the tubing out, about 2 feet from the sidewalk,about 1 foot under ground and into the front yard.
Should they have installed some gravel/sand under ground at the terminus of this tubing?
AsktheBuilder
29 Dec 2007, 16:03
Jim,
I would only have done it if I thought the volume of water would be enough to cause erosion.
Gerard O'Loughlin
19 Mar 2008, 15:04
Hi
I have sand blocking my storm water, can u help on how to move it.

Gerard
AsktheBuilder
21 Mar 2008, 11:17
Gerard,
I would start with a shovel.
Julie
27 Mar 2008, 02:16
Hi,
we are currently looking at a property whereby the storm drainage pipes are above ground running down the side of the property. instead of digging and putting them into the ground would it be feasible to cover with small stones or is it best practice for them to be underground.
AsktheBuilder
28 Mar 2008, 17:10
Julie,
The best practice is to bury them if possible. Make a map or take photos of them during the process. This will make locating them easy in the future.

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