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November 20, 2019 6 min read

Why Downspouts Clog Causing the Need for Leaf Guards:

In my early years working for a roofing and construction company, my superior recognized me as being a very good problem solver and “smoother-over”, so, of course, he began to send me out on all of the problem issues; mainly leaks and drainage issues.   When you spend years visiting persistent or repetitive leaks and issues, you begin to search for and learn commonalities among these projects. At a typical construction firm, many installers are not ever sent back to the problem calls, so they never obtain feedback and never really learn what they might be doing wrong.    Most problems are caused by defects in labor or installation. While of course there can be problems associated with material defects, the vast majority of problems are caused by labor defects; and most of those problems are associated with an installer having too little experience, not being connected with the process of what actually causes problems, just making a simple mistake, or being under pressure to complete the task or project in a hurried fashion.

Over the years, I had the privilege of responding to hundreds of calls with gutters overflowing for all sorts of reasons. Most were rectified by simply  performing typical regular maintenance and  gutter cleaning, but often we would also find that the downspout (AKA leader pipe) was clogged forcing the customer to investigate the purchase of gutter guards.  It was a fairly common occurrence that we would clear that  clogged downspout only to find that in the future it would have a propensity to continue to clog repetitively unless we determined the cause and made alterations to repair that cause.    I found three very common reasons for repetitively clogged downspouts.

  1. Downspout Joint Fasteners Are Too Long and Intrusive

  2. Over Crimping Downspout Connections (not visible, behind the lap)

  3. Insufficient Slope

Downspout Joint Fasteners Are Too Long and Intrusive:  Most downspouts and elbows will easily connect by sliding the male thinner crimped end into the flanged wider female end with a pressure fit such that no joint fasteners are required to stabilize the assembly.  In some cases however, for example where the prefabricated crimed fitting end had to be cut off in order to create the correct custom size pipe, it may be necessary to install a fastener through the joint to keep the downspout or elbow joint from separating and pulling apart.  When a joint fastener is necessary, the experienced and expert installer would traditionally install a very short fastener such as a ⅜” coated zip screw or an aluminum rivet. These short fasteners are best because they grab the sheet metal adequately and most importantly they do not protrude or extend into the inner portion of the downspout obstructing the water flow and catching debris that can cause a clog.   Longer fasteners in the downspouts can often cause an owner to investigate buying leaf guards.  The inexperienced installer sees absolutely no reason why a longer fastener could not be used solely considering the fact that a thin screw surely would not block any substantial amount of water flow, while the experienced technician realizes that the excessively long fastener will stop or trap twigs, leaves and debris. In a 2” x 3” downspout, one unruly screw can grab one thin small twig and the two items have now collectively dramatically decreased the flow size of the downspout such that additional items are now extremely susceptible to becoming hung-up.   As water continues to filter through this partially clogged joint, even smaller debris can continue to collect at an even faster pace on its way to densifying a solid clog and a complete blockage of water flow. Once the homeowner calls for help, typically the contractor will just clear the clog without identifying or repairing the cause because the cause or defect are not visible to the naked eye because one would need ex-ray glasses to see the inside of the downspout. In order to clear the clog and properly keep the clog from returning, the contractor should both clear the obstruction but also remove the unruly fastener and replace it with  a short flow-friendly fastener that will not obstruct water flow and collect debris.

Gutter Elbow Screw

Over Crimping:   These days, most newly installed gutters are typical standard K-style seamless gutters with standard 2”x3” or 3” x 4” downspouts also known as “leader pipes”.  In most cases, the gutter is applied to the fascia of the “soffit” or “Jet”, such that the gutter location is often from 8” to 18 inches further out or “offset” from the home’s siding making it necessary to install 2 “offset” elbows at the top of the downspout so that the downspout can follow the siding down to the ground in a secure and aesthetically pleasing manner.  Assembling the downspout “offset”, typically encompasses attaching 2 identical opposing elbows together and extending them from the gutter outlet tube down to meet the first full length of downspout. Normally these elbows would simply connect together easily using the pre-crimped and flanged male and female factory ends, however to make custom offsets of certain custom sizes, the contractor may need to cut the elbow which might eliminate or “cut off” the factory pre-crimped end.  In such a case when the male end has been cut off, the elbows will no longer fit together unless the contractor “pre-crimps” the “cut-off” end to enable it to fit into the opposing elbow. Often, when the contractor is attempting to fit one elbow into another and pre-crimping or pre-bending inward is required, the less skilled contractor will tend to “over -bend” or over crimp the downspout excessively decreasing the capacity for water flow. While over-crimping will enable the two pieces to fit together, it can also severely decrease the size of the pipe opening, decrease the flow of water,and catch leaves and debris within the pipe..  In some cases, over crimping can make the effective flow size of a 2” x 3” elbow decrease down to 1” x 2”, and this smaller opening will immediately begin to collect twigs and debris and will eventually clog entirely. The experienced contractor will be cognizant of this issue and therefore will crimp the pipe carefully paying attention not to over-crimp. When responding to such a clogged downspout, the intelligent problem solver should both clear the clog but also determine if over-crimping is the culprit and adjust the overly crimped elbow so that it allows maximum water flow and does not stop or trap debris.

Insufficient Pipe Slope:  In order to accommodate many different custom applications, downspout elbows are typically available for purchase with 3 or 4 different angle degrees; in both  front-bend and side-bend styles. Some elbows have angle bends that are very close to 90 degrees. If a 90 degree elbow were attached to a vertical pipe, the result at the end of the elbow is a pipe joint that is very close to being “dead level” or “horizontal”.   When a downspout is assembled and installed with any portion of the pipe being very close to “dead level”, the flowing water becomes very slow at that portion of the pipe and becomes susceptible to a build-up of debris. Due to gravity, a pipe with greater slope has faster moving water that tends to move the small debris through the pipe and conversely less slope tends to allow a build-up of debris and eventually a clog.  Once a partial clog is created, the water continues to filter through that clog continuing to gradually deposit added debris causing the clog to continue to densify and worsen over time. The expert problem solver that arrives to clear this type of clog, might also serve the customer well by eliminating the elbows that created the “level” area and replace them with alternate angled elbows that create and preserve as much positive pipe slope as possible.

There are many reasons why downspouts clog and sometimes it is a simple anomaly. With properly installed downspouts, the need for leafguards is decreased. Often, a contractor will clear the clog and then run the water hose concluding that since the water is flowing out, the problem has been solved; however this is not necessarily true and the positive flow of water from the hose might lull the homeowner into a false sense of security.  The volume of flow from a garden hose does prove that the pipe is no longer completely clogged, but it does not prove that the pipe is allowing maximum water flow. If your downspout clogs once, it is important to clear the clog but if it clogs repetitively, it should be dis-assembled  to determine the reason for the clog and the root cause of the problem should be eliminated so that it will not happen again.

Alex O’Hanley


Alex O'Hanley
Alex O'Hanley

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