What Is a Roof Scupper? Types, Codes and Common Problems

A roof scupper is an opening at the edge of a flat or low-slope roof, usually cut through a parapet wall, that lets rainwater run off the side of the building instead of collecting on top of it. Most scuppers are lined with sheet metal and empty into a collector box and downspout, straight into a gutter, or out into the open air through a short spout. Some are the roof's main drains. Others sit a little higher and only flow when the main drains clog, which is why they are called overflow or emergency scuppers.

We are Patriot Roofing and Restoration in Maumelle. We install and repair commercial and low-slope roofs across Central Arkansas, including TPO, EPDM and modified bitumen, and the scupper is one of the first places we look when a flat roof leaks or holds water. Here is what a scupper does, the main types, why codes care about them, and the problems we see most.

What a scupper does

A pitched shingle roof sheds water on its own. A flat roof with a parapet (a short wall that rises above the roof around its edge) is more like a shallow tray: water has to be led to a way out. The two ways out are interior drains, which take water down through pipes inside the building, and scuppers, which take it out through the wall at the roof edge.

That matters in Central Arkansas. The National Weather Service's 1991 to 2020 normals put Little Rock's average rainfall at 50.42 inches a year, with April the wettest month at 5.59 inches. A flat roof that cannot get that water off quickly carries it as weight, and standing water finds every weak seam.

The main types of roof scupper

• Through-wall scupper. A rectangular opening through a parapet wall, lined with a formed sheet metal box that is flashed into the roof membrane. This is the most common kind.
• Scupper with collector box and downspout. The scupper empties into a metal box on the outside wall (also called a conductor head or leader head), which feeds a downspout to the ground. This keeps water off the wall and walkways.
• Open or extended scupper. A spout that sticks out past the wall and lets water fall freely. Simple, but it can stain the wall and drop water on whatever is below.
• Overflow (emergency) scupper. Set above the main drains so it only carries water when those drains are blocked. It is a backup, not the main drain.
• Scupper into a gutter. On a roof edge without a tall parapet, a scupper can empty straight into a gutter.

Why building codes care about scuppers

The danger on a flat roof is not just a leak. If the main drains clog during a heavy storm, water keeps building until something gives. The National Roofing Contractors Association (NRCA) explained in its Professional Roofing magazine (Mark S. Graham, April 2018) that the International Building Code requires secondary roof drains or scuppers "when the roof perimeter extends above the roof surface," because water can be trapped "if the primary roof drains are clogged."

The International Institute of Building Enclosure Consultants (IIBEC) summarized the building code rules in a 2017 article by Wanda Edwards, PE: the quantity, size, location and inlet height of overflow scuppers have to keep ponding water below the depth the roof structure was designed to carry, and a scupper opening must be at least 4 inches. Roofs also have to be designed for the rainwater that would build up if the main drains were blocked.

The same sources note an exception that matters when a roof is replaced: under the International Building Code, secondary drains or scuppers generally do not have to be added on a reroof if they were not there before and the roof drains properly, though the separate existing-building code has been read differently. The sizing math belongs to the building's designer or engineer and the local building official, so ask before a reroof whether your building needs overflow scuppers added.

How a scupper should be built

NRCA's technical column in Professional Roofing (Joan P. Crowe, January 2007) laid out several points from its roofing manual details for through-wall scuppers:

• A two-piece sheet metal assembly: a liner on the inside of the opening and a closure flange on the outside of the wall.
• Joints soldered or welded, not just caulked.
• Where the scupper is the main drain, its base set level with the roof surface so water can actually reach it, rather than perched at the height of the membrane layers.
• The top of a collector box set about 1 inch below the bottom of the scupper.
• A drainage sump at the scupper opening (a slight low spot built into the insulation) to pull water toward it.

The column also points out that the scupper area has many seams and attachments, so it should stay free of standing water. That is where a lot of flat roof leaks begin.

Common scupper problems

• Clogs. Leaves, seed pods, balls, bird nests and loose gravel collect at the opening, and the roof behind it ponds.
• Failed flashing. The seal between the metal liner and the roof membrane cracks or pulls loose, and water runs into the wall or the building.
• Scupper set too high. If the opening sits above the roof surface, water stands in front of it after every rain.
• Undersized openings or collector boxes. In a downpour the box overflows and water sheets down the wall.
• Rust and open seams. Older galvanized liners rust through, and caulked seams open up with heat and cold.
• Wall staining and damage below. An open scupper with no downspout can stain masonry and wear out the ground below it.

Leaks around a scupper are a flashing problem at heart, the same as leaks at a chimney or wall on a pitched roof. Our guide to roof flashing and where leaks start explains why those junctions fail.

Scuppers on homes

Scuppers are not only for warehouses and churches. Some homes have a flat roof over a porch, carport, addition or garage with a short wall around it, and those sections often drain through a scupper. The same rules apply: keep the opening clear, make sure water reaches it, and have the flashing checked if you see stains on the wall below it or the ceiling under it. Flat sections on a home take a different roofing system than the shingled slopes, so in our roof replacement estimates a flat section is priced at the inspection.

How to look after a scupper

• Look at the roof after a heavy rain. Water still standing near a scupper a day or two later is a sign of a clog, a scupper set too high or a low spot.
• Clear debris from the opening and collector box, especially in fall. Only go on a roof if you can do it safely; otherwise have a roofer do it.
• Check the downspout below runs freely and empties away from the foundation.
• Watch for rust streaks, open seams and dark stains on the outside wall below the scupper.
• Have the flashing at each scupper checked during any roof inspection, along with the drains and the membrane seams.

Frequently asked questions

What is the difference between a scupper and a roof drain?

A roof drain sits in the roof surface and carries water down through pipes inside the building. A scupper carries water out through the edge of the roof, usually through a parapet wall. Many flat roofs use drains as the main system and scuppers as the overflow.

What is an overflow scupper?

An overflow or emergency scupper is set higher than the main drains, so it only carries water if those drains clog. Its job is to stop water from piling up on the roof to a depth the structure was not designed to hold.

Why is water coming out of my overflow scupper?

If an overflow scupper is running, water on the roof has risen above the main drains, which usually means a main drain is clogged or cannot keep up. Have the drains checked and cleared.

Can a leaking scupper be repaired, or does the roof need to be replaced?

Many scupper leaks are repaired by cleaning out the opening and replacing the liner and its flashing into the membrane. If the membrane around it is worn out or the roof ponds widely, a larger repair or replacement may make more sense. An inspection tells you which.

Get your flat roof and scuppers checked

If water is standing on your flat roof or showing up on a wall or ceiling near a scupper, contact Patriot Roofing and Restoration. Commercial roofs are quoted in writing after an on-site inspection. For a home, a roof repair visit is $79.99 and includes our 21-point roof inspection, and Patriot Care Club members pay no service fee. See our commercial roofing page for the systems we install.