Got rain? How to carry the water to the right spot

September 9, 2011

T he downspouts from my roof empty out right next to my home. I think this contributes to my wet basement. I know it keeps my grass soggy. Friends tell me to just install the simple plastic downspout diverters or splash blocks and all will be well. I’m convinced those are pretty much useless. What’s a good long-term solution to dealing with lots of roof water?

You’ve got good reason to be concerned with rain water that cascades down roof slopes. Houses equipped with gutters and downspouts concentrate this water in just a few locations where the downspouts terminate near the ground.

You’re correct that the downspout splash blocks or diverters, as some people call them, are of little benefit. The only thing they do is absorb some of the downward energy of the water as it rushes down. Without the splash blocks, you’d have a large hole next to your home where soil used to be.

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 an 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 crawlspaces.

It has always been my feeling that roof water should be piped to the lowest spot on the property, into municipal storm water 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. (Note that in some parts of the country, it is forbidden to store this water because of water rights that were sold or leased many years ago. Someone downstream of you may have negotiated the rights to get the water that falls naturally out of the sky.)

I’ve had nothing but success piping roof water underground in rigid PVC pipes. I like to use a pipe that’s made for sewer-line work. It comes with slip joints that don’t have to be glued. This pipe does not have the wall thickness of Schedule 40 PVC, but it’s not the flimsy ABS plastic piping that you’ll commonly see at the home centers. You can find this SDR-35 PVC pipe at quality plumbing supply houses or businesses that sell pipes to sewer contractors.

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 sure they fall a quarter-inch per foot of run. This provides plenty of pitch so the water readily flows.

You’ll want to use a four-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 I would use a 90-degree bend is at the end of the pipe where it turns up to capture the end of the metal downspout.

To make other 90-degree bends in the piping system, use two 45-degree bends and put a one-foot piece of straight pipe between them. This spacing will help if you ever have to put a drain-cleaning snake down the pipe to unclog it.

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 go naturally.

Tim Carter is a columnist for Tribune Media Services. He can be contacted through his Web site, askthebuilder.com.

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