Are The Downspouts on My Seattle Roof at Risk of Clogging?

Are your gutters overflowing during heavy Seattle rain even though there doesn’t seem to be enough debris inside them to cause a clog? Are you worried that a downspout you rarely think about could suddenly back up and send water over your gutters, potentially damaging your siding, foundation, or roof?

At RoofSmart, we’ve helped hundreds of Seattle-area homeowners troubleshoot gutter and drainage problems. One thing we’ve learned is that it doesn’t take a gutter that is already completely full of debris to cause a serious clog. Sometimes, one strategically placed leaf or a small clump of pine needles over the downspout opening is enough to restrict the entire drainage system.

In this article, we’ll explain why downspouts are often the choke point of your gutter system, how to determine whether yours are vulnerable to clogging, and what you can do to keep water moving off your roof, including the different precautions you’ll need if you have a flat roof.

Common Causes of Downspout Clogs and the Best Solutions

What makes downspouts vulnerable to clogging?

You want to think about how much surface area is going to a given drainage area. To break it down further, think about how much surface area the downspout is going to try to catch and drain.

People almost always focus on the size of the gutters for carrying capacity, but that's not the only important factor. The only way that the carrying capacity of the gutter makes a difference is if the water can make it laterally to the downspout. But the downspout is really the choke point.

A single piece of debris can plug a downspout's 2" opening. This is a huge concern in Seattle and the surrounding areas because there are trees all over and many homes are surrounded by them.

For example, this gutter doesn’t have very much debris in it, but the downspout on the far left is halfway covered with small debris.

A leaf can easily fall into the gutter and then get plastered over the top of a downspout. Or some pine needles can collect and clog the downspout. A lot of people are under the misapprehension that it takes a lot of debris to plug the gutter, but it just takes the right debris.

So around 500 square feet of roof area can be drained by one regular two-by-three downspout. About 450 square feet of roof area can be drained by a three-inch round downspout. And about 1,200 square feet can be drained by a three-by-four downspout.

The gutter system needs to catch it as it comes off the roof. The downspout, though, is what gets it out of there. And that's why when those clog, everything goes bad.

How can I prevent my downspouts from clogging?

To make sure that the gutter and downspout system on your roof works properly, these are the factors you need to keep in mind:

• The gutter needs to be able to catch water: Make sure that your gutters are the right size for the drainage area that you’re directing water from. You should also make sure that they are installed at the right angle with the roof to successfully catch water and are sloped downward slightly toward the downspout to help water naturally flow in that direction.
• Note that standing seam metal roofs require larger gutters to catch the water running off the roof because the water moves so much faster on the smooth, slippery surface.

• Have the right size downspout for the roof area: If your downspout is too small or if it clogs easily, then your gutters and downspout are going to get blocked all of the time. This could easily result in overflowing gutters, which can damage your home’s foundation, or potentially cause your siding to rot.
• Make sure it doesn’t clog: A great way to protect your downspout from clogging is by installing gutter guards. Gutter guards are essential for maintaining flow because they prevent debris from entering the gutter or even touching the downspout. However, when choosing gutter guards, it’s important to do a lot of research to find the right gutter guard for you. A lot of gutter guards don’t work the way you think they will, resulting in debris clogs on the gutter guard. At RoofSmart, we have a guide to help you pick the best gutter guard for your Seattle home. Our personal favorite is MasterShield because it is sloped to shed debris and is designed to prevent algae growth. These two things protect it from clogging.

How do I avoid downspout clogs on my flat roof?

When it comes to flat roofs, drainage systems are a completely different story. There are no gutter guards or even extra gutters. Everything happens on the actual roof.

The best way to avoid (or deal with) clogged scuppers on a flat roof is to:

• Have plenty of secondary drains

• Get on the roof and unclog the scupper

There isn’t really a way to sugarcoat it when you have a flat roof. It’s easy for a lot of leaves, pine needles, and other debris to build up on the roof and clog the scupper. You have to be able to scoop this debris up so that water can flow down the scuppers instead of pooling up on your roof.

There are different types of scuppers, but through-wall scuppers are best if you want to make sure that scupper clogs don’t lead to internal leaks. And having plenty of secondary scuppers means that your roof isn’t at risk when just one scupper clogs because it has other options for draining the roof.

Preventing too much standing water from collecting is crucial when you have a flat roof or a rooftop deck.

Could your roof layout be causing your gutters to overflow in Seattle?

Keeping your downspouts clear is important because even a small amount of debris can create a clog that prevents your entire gutter system from draining properly. Choosing the right downspout size, installing effective gutter guards, and regularly clearing scuppers on flat roofs can all reduce your risk of clogs and water damage.

But a clogged downspout isn’t the only reason your gutters might overflow. If you’ve cleared your gutters and downspouts and water still pours over the edge during heavy rain, the problem could actually be the way your roof directs water.

Certain roof layouts can concentrate a large amount of runoff into one small section of gutter, overwhelming a drainage system that would otherwise be properly sized.

Read our article “Is the Layout of My Roof Causing My Gutters to Flood?” to learn which roof designs are most likely to overwhelm your gutters and what custom drainage solutions can help control the water before it causes damage.