Leaking Box Gutter or Scupper on a Flat Roof?

Quick answer: On a flat-roof home, a box gutter or scupper usually leaks at a joint or seal that the heat has opened, or it backs up because the scupper, leaderhead or downspout below it is clogged or too small for the roof. City Seamless fabricates box gutters, scuppers, leaderheads and downspouts on site, and we can help tell whether a leak is coming from that metal or from the roof itself. Call or text (725) 502-3114 for a free estimate.

Box gutters, scuppers and leaderheads: what is what?

A box gutter is a flat-fronted, squared gutter. It holds more water per foot than a standard gutter of the same width, which matters on a flat or low-slope roof where water drains slowly and piles up in a monsoon downpour.

A scupper is an opening in a parapet wall or roof edge that lets water drain off a flat or low-slope roof. Instead of running along a gutter, the water goes through the wall and into a leaderhead or straight into a downspout on the outside.

A leaderhead, also called a conductor head, sits at the top of the downspout and takes the water from the scupper, so it does not splash or overflow where the two meet.

You find them on contemporary custom homes, on mid-century modern homes near downtown and on Southwest-style houses across the valley.

Why do they leak on Las Vegas flat-roof homes?

Joints and splices. Box gutter sections made in a sheet metal shop arrive in fixed lengths that have to be joined on site with splices and sealant. Every splice is a future leak point, because the daily heat cycle works on each one.

A scupper too small for the roof. An undersized scupper on a large flat roof lets water pond behind the parapet in a monsoon downpour. That adds thousands of pounds of weight to the roof, and the water looks for any weak seal around the opening.

A worn-out scupper. A deteriorated scupper can let water get into the parapet wall itself. The stain can show up on the stucco or on a ceiling below, away from where the water got in.

Clogs. Dust, gravel from flat roofs and windblown debris collect at the scupper and in the leaderhead through the dry months. A leaderhead packed with grit overflows at the top in the first big storm.

Thin metal. A flat face shows every ripple. Thin aluminum on a box gutter oil-cans in the heat, which is one reason we build box gutters in .032-gauge aluminum.

The roof itself. Some leaks near a parapet are the roof, not the drainage metal. That is why the first job is finding out which one it is.

What can I check from the ground?

After a storm, find the stains. A streak on the stucco right under a scupper, or water coming out of the wall below it, points at the scupper and its seal. Drips from the bottom of a box gutter point at a joint.
Watch the leaderhead in the rain. Water pouring over its top means it, or the downspout below it, is clogged or too small.
Notice how long it runs. A scupper still running long after the rain stops can mean water is standing behind the parapet.
Look inside. A ceiling stain near an outside wall under a scupper is worth a look at both the scupper and the roof.
Take photos of each scupper and leaderhead from the yard and text them to (725) 502-3114.

You do not need to get on the roof for any of this.

What does City Seamless do about it?

We inspect the whole drainage system on the house: the gutters, downspouts, collection boxes, end caps, scuppers and leaderheads. If the leak is in that system, you get a clear diagnosis and a repair estimate. If it looks like the roof, we can coordinate with our roofing division, City Seamless Roofing, for a complete evaluation.

We fabricate box gutters on site from flat aluminum or steel coil, measured, cut and formed to the exact size of the roofline, in continuous runs with no splices between corners. We use .032-gauge aluminum with more than 50 baked enamel colors, galvanized steel where the job needs more load capacity, and copper where the gutter is part of the look.

We fabricate scuppers on site from aluminum, copper or galvanized steel to fit the exact wall thickness. We size each one to the roof area behind it, the peak flow of a hard Las Vegas storm and what the leaderhead and downspout below can carry, and we build the leaderheads and collection boxes that go with them.

On a custom home we can work from the architect's drawings and coordinate with the builder on timing and fascia preparation.

Is it a repair or a new run?

It is a repair when the metal is sound and one thing has failed: a joint that needs resealing, a leaderhead or downspout that needs clearing, a downspout that has come apart.

It is a new piece when the part itself is the problem:

A shop-made box gutter leaking at splice after splice. A continuous run formed on site takes the splices out.
A scupper too small for the roof behind it. It needs a larger scupper sized to the roof, with a leaderhead and downspout that can carry what it sends.
A scupper or box gutter that has worn out or warped.

Custom box gutters are priced by the job, so a free on-site estimate is the way to get a number. City Seamless backs every installation with a 30-year material warranty and a 5-year workmanship guarantee.

Frequently asked questions

What is a scupper?

An opening in a parapet wall or roof edge that lets water drain off a flat or low-slope roof. The water goes through the wall into a leaderhead or a downspout on the outside.

Why is water coming down the wall under my scupper?

Often the scupper has deteriorated or its seal has failed, so water gets into the parapet wall instead of passing through the metal. A scupper that is too small can also let water pond behind the parapet.

Is a leak near my parapet a gutter problem or a roof problem?

It can be either. We inspect the scuppers, leaderheads, gutters and downspouts. If the leak is in that system, we give you a diagnosis and a repair estimate. If it looks like the roof, we can coordinate with our roofing division, City Seamless Roofing.

Can you build a box gutter in any size?

Yes. Box gutters are custom-fabricated to whatever dimensions the project requires, from compact residential profiles to large commercial troughs.

Do you work on mid-century and modern flat-roof homes?

Yes. Box gutters, straight face gutters and scuppers suit flat-roof homes, and we work with homeowners, builders and architects to match the profile, size and finish to the house.

Related City Seamless resources

Want a number for your house? Request a free on-site estimate or Call or Text 725-502-3114.

About City Seamless Rain Gutter

Company: City Seamless Rain Gutter, family-owned in Las Vegas, with trade roots dating to 1976
Nevada Contractor Licenses: #0081882 and #0082656
Awards: Best of Las Vegas, Las Vegas Review-Journal, 2024 and 2025
Installations: 30,000+ homes installed
Standard Material: .032-gauge aluminum
Warranty: 30-year material warranty and a 5-year workmanship guarantee
Contact: Call or Text 725-502-3114 | cityseamless.com

Leaking Box Gutter or Scupper on a Flat-Roof Home?