Q&A / 

Downspout Drainage Pipes

Downspout Drainage Pipes

Every year tens of thousands of homeowners suffer from water seepage into their homes caused by non existent or poorly constructed downspout drainage systems. Homeowners who are blessed with sandy, well-drained soils escape this problem.

However, a majority of homeowners in the nation face problems with clay-rich soils. Certain clay soils are very resistant to water infiltration. In general the deeper you go in a soil the tougher it is for water to flow. Water builds up in the upper layers of these soils and looks for a place to go. Often that can be your basement, crawl space, or the lower level of your split-level house.

Soil is made up of solid particles, organic matter, liquid water, and gas. The gas usually happens to be air. After a rain this air oozes to the surface as it is replaced by the heavier water.

The upper layers of soil usually have the highest air content. The greatest amount of water content and water movement usually takes place in the upper 2 feet or so of most clay soils.

Splash Blocks

Just before writing this bulletin I received a book that shows how to make your own concrete splash blocks. These features are common on many homes here in Cincinnati and across the nation. Builders and remodelers have installed these simple 'energy absorbers' for decades. The splash blocks absorb the energy of the falling water. If you think they keep water from collecting around your foundation, well, I've got this bridge I'd like to sell you...

Long-Term Solutions

The rainfall that falls on an average roof can be tremendous. A typical house in the Chicago area can have in excess of 50,000 gallons of water fall on the roof in just one year. My roof in Cincinnati will capture about 145,000 gallons this year. Allowing your roof water to simply discharge onto and into the soil around your house is a big mistake.

The solution is to pipe it away from your house. Some areas allow you to discharge this water onto the soil at the lowest part of your lot. Other cities may require you to hook up your downspout drains to a city storm water system. Whatever the case may be, you want to get the water away from your house.

Perfect Pipes

As with many things, there are choices with respect to drainage piping materials. There are two types of piping I find to be inferior: the black corrugated pipe and the thin-wall 1500-lb.-crush-weight plastic pipe. I dislike these pipes because they crush easily and are tough to clean out should a clog develop and because roots can grow into their joints.

Instead, I choose to use pipes with smooth inner surfaces, thick crush-resistant walls, and tight-sealing joints.

There are two piping materials I'm aware of, both are made from PVC, that meet these criteria. The best material is Schedule 40 PVC. This is the pipe that you see used for indoor sanitary plumbing purposes. The pipe wall thickness is very substantial. The fittings are welded to one another with a special solvent. When dry, you can not separate the pipes. Roots can not penetrate.

The other pipe I like to use is called SDR 35. It is a lighter weight PVC pipe that is used primarily for sewer pipe work. I prefer to use the pipe that has special male and female ends. The female end has two durable rubber gaskets that seal the male connection. This pipe does not leak! You simply coat the rubber with liquid dishwashing soap and push the male end into the hub of the female fitting. BINGO, a solid leakproof connection. The fittings work the same way.

I always use 4-inch diameter pipe for downspout lines. This size can handle vast quantities of water. It is also easy to clean out should a clog develop.

Turning Corners

I am a licensed master plumber. I was taught years ago that it is a bad practice to install right angle fittings below ground. Right angle fittings are generally considered 90 degree elbows. These fittings slow down water flow and make it difficult to rod out or clean out a clogged pipe.

If you need to make a 90-degree bend, simply use two 45-degree fittings separated by a small (1 foot) length of straight pipe. If you can put a longer piece in between the two 45's, all the better!

Ninety degree elbows can be used where the buried downspout drain line turns up to capture the actual downspout. In addition to this fitting, you may wish to add a tee or wye fitting just as the pipe exits the soil. This extra fitting can be used as a nifty cleanout. In the event of a clogged pipe, you do not have to remove the downspout from the hub. You simply insert the cleaning snake through the cleanout.

Column B112

SPONSORS / 

2 Responses to Downspout Drainage Pipes

  1. Tim,

    As a former Engineer (it has been more than a while), I am facing a home project exactly like what you are describing in this article. I am planning to use Schedule 40 PVC like you discuss. Do you have a good calculator that will show the best way to calculate the drain pipe sizing as we connect the multiple roof drains together into a common header for discharge?

    Thanks.

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>