How Build An Underground Downspout Extension To Carry Water Away From Your Home

If you have gutters on your home, then you can probably appreciate their effectiveness in keeping water runoff from eroding the soil surrounding your home. However, gutter downspouts can sometimes pose a challenge to homeowners by concentrating the flow of water into one location. This can lead to a high volume of rainwater pooling near your home's foundation and seeping into the space between the foundation and soil. French drains can help alleviate some of the problem, but a better course of action is carry excess water away from the side of your home altogether. Below is how you can easily build an underground downspout extension that will carry rainwater away from your home:

Tools and materials needed

  • Grated downspout filter with flexible connector

  • Ten feet of 4-inch diameter PVC pipe

  • Six-inch piece of 4-inch diameter PVC pipe

  • Tee-connector for 4-inch diameter PVC pipe

  • 4-inch plastic drain grate

  • 50-pound bag of pea gravel

  • Post hole digger

  • Shovel

  • Screwdriver

  • Silicone adhesive and caulk gun

Step-by-step procedure

1. Replace the downspout elbow with a grated downspout filter - It is important to prevent your underground downspout extension from filling with debris. Leaves, pine needles, and soil will clog the downspout extension and eventually necessitate extensive cleaning or removal altogether. An easy solution to this problem is replacing your downspout elbow with a grated downspout filter; this specialized filter contains a grate mounted at a 45-degree angle inside the body of the filter. This device captures debris which is then swept out of an opening by the force of the falling water.

Remove the downspout elbow by unscrewing all the sheet metal screws that hold the elbow in place, then simply pull the elbow off the downspout.

Once you have removed the downspout elbow, slide the end of the grated downspout filter over the elbow and secure it in place using sheet metal screws. If the connection does not feel secure, then you can reinforce it by caulking the seams with a clear silicone adhesive.

2. Dig a trench for the PVC pipe - The next step is to dig a shallow trench from your downspout to the point where the PVC pipe releases the rainwater. Make the trench about 10 inches deep and 6 inches wide, but just be sure that you can completely cover the PVC pipe with soil once you are finished with the project.

At the end of the trench, use post hole diggers to dig straight down into the soil about 2 additional feet. This hole will serve as the drainage field for the rainwater and will be filled with pea gravel to prevent erosion and soil subsidence. Pour enough pea gravel into the hole so the top of the gravel is flush with the surrounding bottom of the trench.

3. Install the PVC pipe - Drop the PVC pipe into the trench and attach the flexible end of the grated downspout filter to the pipe by sliding the two ends together. No cement should be necessary to join the ends of the filter and PVC pipe, since the installation will be held immobile by the surrounding soil.

4. Attach the tee and drain grate - At the opposite end of the PVC pipe, slip the tee connector over the end of the PVC pipe so that one tee opening points up and the other tee opening points down into the gravel-filled hole. On the open end of the tee facing up, slip a 6-inch piece of PVC pipe into the opening and slip the drain grate on to the other end of the 6-inch piece of pipe. The drain grate exists to provide an overflow location for water that can't drain into the gravel-filled hole and to provide an easy-access cleanout for maintenance purposes.

Carefully backfill soil around the completed assembly so that the pipe is completely buried except for the top of the drain grate. If the drain grate extends up more than about an inch above the surrounding surface of the soil, cut one inch from the end of the 6-inch piece of pipe and reassemble the grate and pipe. The drain grate should not protrude too much above the ground or you may strike it with a lawn mower.

5. Fill in the remaining soil - After securing the grated end of the drain, backfill soil all along the remaining distance of the PVC pipe. Firmly pack soil around and underneath the pipe to provide support and prevent subsidence of the soil.

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