Are you worried that your flat roof might be holding water or that a hidden drainage issue could lead to leaks and expensive rot inside your home? Has your roofer mentioned scuppers, leading you to wonder if your current setup is putting your roof at risk?
At RoofSmart, we have installed and repaired hundreds of rooftop decks across the Seattle area. Scuppers are a main leak point because they are a vulnerable area that is usually sealed improperly. Or, they get clogged and get no relief because there aren’t secondary scuppers. It often leads to tens of thousands of dollars in damage.
In this article, we’ll break down the different types of scuppers, how they work, and which options are safest for Seattle homes. You’ll also learn why secondary overflow scuppers are so important and how to make sure your flat roof drains properly to avoid leaks and rot.
|
Scupper Type |
How It Works |
Risk Level |
Main Advantage |
Biggest Risk |
|
Internal Drain Scupper |
Drains water through roof into internal pipes |
⚠️ High |
Hidden, clean appearance |
Leaks occur inside walls if clogged |
|
Through-Wall Scupper |
Drains water through wall to exterior downspout |
✅ Low |
Water exits outside the home |
Visible overflow if clogged |
|
Primary Scupper |
Main drainage point at lowest roof level |
⚠️ Moderate |
Handles normal water flow |
Can clog and cause ponding |
|
Secondary Overflow Scupper |
Backup drain placed higher on roof |
✅ Low |
Prevents water buildup if primary fails |
None (critical safety feature) |
|
No Secondary Scupper |
Only one drainage point |
❌ High |
Lower upfront cost |
High risk of standing water and leaks |
|
Poorly Installed Scupper |
Improper sealing or placement |
❌ High |
None |
Major leak point regardless of type |
Scuppers are the drains installed in flat roofs and rooftop decks. They are usually located in various spots along the outer edge of the roof.
No matter what kind of flat roof material you use or what the layout of your roof is, every flat roof (and rooftop deck) has scuppers. Without them, your roof will fill up with water and debris.
There are two main kinds of scuppers:
Internal Drains: These are set up to drain down through the roof deck into internal pipes built into the walls of your home. This type of scupper has a high risk of catastrophic leaks if clogged because the water and debris get stuck inside your wall. So, when it inevitably springs a leak, it’s going to happen inside your walls. This creates a huge mess and leads to rot within your walls. This happened to one of our customers once. The clog started at the base of the downspout of his internal drain, so water backed all the way up the downspout to the roof. As a result, it started leaking and essentially looked like a fountain inside his wall. Despite this risk, internal drain scuppers are still fairly common in the Seattle area. This is an example of what an internal drain scupper looks like:
Through-Wall Scuppers: These scuppers actually drain water through the wall out to a downspout installed on the exterior of your home. This is a much safer option because if it clogs, then it will overflow on the outside of your roof and walls. It’s still a mess, but not one that causes the inside of your walls to rot out. This is what a through-wall scupper looks like from the roof:
And this is what a through-wall scupper looks like from the outside:
All scuppers are supposed to be installed slightly lower than the height of the roof to help with drainage. Flat roofs are also meant to be tapered to direct water toward the scuppers.
Primary scuppers are the main scuppers installed on the roof at the lowest point. Secondary scuppers are installed a little bit higher up on the roof. Their job is to provide an extra place for water to drain if the primary scuppers get clogged and too much water starts collecting.
Secondary overflow scuppers prevent internal leaks on the roof because they keep it from having too much excess standing water. Any time there’s standing water on the roof, there is a chance that the water will find a weak spot and cause a leak.
Secondary overflow drains give your roof extra protection in case of an emergency, but it’s also important to remember that all of your scuppers need to be installed correctly. If not, then the scuppers themselves can start to leak and damage your roof.
Torch down is a difficult material to bend and flex because it is so thick, which means that a lot of drains on torch down roofs are done poorly and leak. If you want a torch down roof, you need to make sure that you hire an experienced roofer who can properly install the scuppers.
Secondary overflow scuppers are required for all new construction homes. They are not required on already existing flat roofs, but we do highly recommend adding them when you are replacing your flat roof.
Cities and neighborhoods across the Seattle area with lots of trees always collect a lot of debris on rooftops. This can cause issues on any roof, but flat roof scuppers can get clogged with leaves, pine needles, and other tree debris very easily.
In an area with a lot of trees, often we will actually recommend that we get rid of scuppers and do gutters so everything just spills over the edge (like on a regular roof).
This helps reduce the amount of maintenance needed on a flat roof. If you have traditional scuppers, you’ll need to make sure that you clean debris off your roof regularly.
Without secondary overflow scuppers, your roof will continue to fill up with debris and water. The number one risk on a flat roof is a leak, and when you have standing water, a leak is much more likely to happen.
Flat roof leaks can cause devastating amounts of damage because they can go on for months or even years before anyone discovers the leak. This is more than enough time to spread moisture throughout the inside of your roof and completely rot it. By that point, you have to replace everything, which gets very expensive.
As you’ve learned, choosing the right type of scuppers and making sure they’re installed correctly is critical to protecting your flat roof from standing water, leaks, and long-term rot. Whether it’s selecting safer through-wall scuppers or adding secondary overflow drains, these details are what keep water moving off your roof instead of sitting and causing damage.
But scuppers are only part of the drainage system. If water isn’t properly managed once it exits the scupper, it can still back up, overflow, or concentrate in ways that put your roof and walls at risk.
Missing components, like leader heads, can quietly create the same kinds of problems you were trying to avoid in the first place.
Read our article “Can Water Quietly Destroy My Flat Roof with No Leader Head in Seattle?” to learn how water behaves after it leaves your scuppers and why proper drainage design is essential for preventing serious damage to your flat roof and home.