How to Install Downspout Extensions

There are many types of extensions you can use to drain water from your downspouts a safe distance away from a building to protect the foundation, crawl space or a basement. Installations are not that difficult at all, but you will need to know what kinds there are and choose the one that best suits your needs. Below are some choices.

Horizontal rigid extensions

• Horizontal rigid extensions help to protect both foundation and foundational plantings.  

1. Install a horizontal extension through the planting area over top of mulch and draining out at least six feet from the foundation onto a splash block or into a dry well. 


2. Consider hinged extensions or swing-up extensions as they are another good alternative.  


3. If you have a downspout that empties into a high traffic area near a walkway, you might want to install one with a manual hinge that can be lifted up out of the way when it is not raining.

Flexible extensions

• Flexible extensions are good as they can be directed around plantings and through openings in border stones. 


• Allow gravity to drain the downspout several feet away from the foundation.  

1. Find the edge that fits the end of your downspout, but do not attach just yet.  


2. Extend the flexible extension all the way out its full length.  


3. Trimming can be done with an exacto knife. 


4. Attach the end that fits the spout snugly.

Rollup extensions

• Rollup extensions are flexible in that they are fully extended six feet from the home when it is raining and until the roof has drained.  


• They retract back to the end of the downspout when dry.  

1. Shorten the length of the existing spout using a hacksaw while still in place or you may have to remove it and then shorten.  


2. Slip the spout into the automatic extension device and attach to the side of the home drilling holes for anchors that will accept the masonry screws provided.

Underground extensions

• These extensions empty into a pipe and are buried in a trench 10-inches deep and six-inches wide.  This trench empties into the sewer line at the street.  


• You will need to contact your locality’s street department for how to tap into the sewer as these may differ in some areas.  

1. Mark out the trench run and dig it sloping downward slightly about one to two inches to provide gravity for the water. 


2. Install a downspout adaptor and coupling to the end of the spout with some zip screws.  


3. Take a 90 degree elbow placed in the trench directly beneath the coupling and measure distance between coupling and the edge of the elbow.  


4. Cut a length of PVC the same diameter as your spout coupler with a hacksaw in the measurement just taken. 


5. Apply primer and then cement to both ends of this pipe and connect the two.  


6. Cut another length of PVC to line the trench and attach this pipe to the elbow using primer and cement again.  


7. After all connections are made,  refill the trench. 

• Underground extensions that are connected to the downspout in the same manner as one running to a sewer line can instead run out and empty into a gravel dry well at least six feet from the foundation. 


• Dry wells are usually about 24” in diameter and 18” deep and filled with gravel.