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  • Writer's pictureBlue River Gutters

How to Assemble and Install a Downspout Extension

Updated: May 13

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What is a Downspout Extension?

A downspout extension is a piece of material that extends the downspout from the foundation wall to safe area away from the structure. Downspout extensions are made from many different materials. They come in many different lengths and are usually used to carry water out into a yard or area where water can naturally travel away.

Why Do I Need a Downspout Extension?

The landscape or ground around a residence can be angled or pitched in a way that controls the flow of water. Water can accumulate in certain areas causing water to stand or puddle. When a downspout terminates directly at the foundation, water can damage your foundation even if you are using a splash block. The splash block does a good job of slowing down the impact of the water but you still have the problem of accumulation. Sometimes a splash block is considered a downspout extension although it doesn’t move water away from a building nearly as much as other types.

Assembling a Downspout Extension

Assembling a downspout extension is probably the number one DIY project that anyone can handle. This project is extremely easy depending on which product you choose. Most big box stores will sell some type of an easy-to-assemble downspout extension. It will usually be something that is flexible, solid, and you can roll it out during a rainstorm. If you decide to buy a kit from the store, be sure that you purchase the one that’s going to fit your size downspout.

Measuring the Outlet

To install a downspout extension properly, measure the outlet located at the bottom of your downspout. This is usually going to be  two by three or three by four inches. Sometimes you may find a three inch round or a four inch round downspout. These products are easy to confuse when shopping for them, but you can find them in these traditional sizes. Usually there is not much assembly required. Most of these products are preassembled, snapped together, or made out of just one piece.

Connecting the Downspout Extension to the Elbow

Once you know that it fits over the bottom of your downspout, you are ready to connect it. You can either remove the bottom elbow and connect the extension directly or simply connect the extension to the end of the elbow. How you do it will be based on cosmetics or the material your downspout extension is made of. Just be sure the water flow goes inside the extension so it doesn’t leak.

Another thing to consider when installing a downspout extension is whether or not the downspout and its elbow are too long and extending too close to the ground. Make sure the angle of water flow isn’t going backwards. It might be necessary to cut the length of the downspout.

Sealing the Downspout Extension

The joint between the extension and the downspout is not sealed so finding the correct angle will help make sure it doesn’t pop off. If you think it is necessary you can buy some Snap-On attachments or Zipp screws to hold the extension in place.

Maximum length of the Zipp screws should be only a half an inch. Do not use a screw longer than a half an inch, especially if you do not have gutter guards. Long screws extending into the inside of a downspout can catch small twigs, leaves and debris and cause the downspout to stop up quickly. Just a few leaves catching on a two inch screw can cause problems.

Cutting the Downspout to the Right Size

Tin snips or a hacksaw can be used to cut the bottom of a downspout or you can consult a professional to help. Raising the downspout to a level that is above the high ground is important when installing a downspout extension. Water and debris can build up and clog the downspout if this is not considered.


Check around your home to see if there are any low spots and always purchase a downspout extension to get rain water to a safe zone. If your budget is right you can settle for a splash block. In a case where you need to go farther than eighteen to twenty four inches, the downspout extension will be your best option.

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