A Scupper Through the Parapet Is Not a Gutter Outlet

A flat or low-slope section of a St. Louis house often has no gutter at all. Water on that section runs across the roof surface to a scupper, which is an opening cut through a parapet, a short wall or the roof edge, and then falls into a downspout or a conductor head. The scupper does the job a gutter does on a pitched roof, and it has its own failure points. If the opening sits too high, is too small, or is blocked by a pile of leaves or a plug of ice, the water stays on the roof and finds its way in at the seams.

Gutters and guards: where the water has to go

Start with the roof surface, not the outlet. Water on a flat section moves toward the lowest point, and that point needs to be the scupper. A roof that looks level from the yard can have shallow low spots that hold an inch of water after a heavy rain. When the scupper sill sits above those low spots, water pools behind it and stays there until it evaporates, freezes or finds a gap.

A parapet adds a second problem. The parapet is the short wall that rises above the roof edge, and it can trap water on the roof side when the outlet is undersized or set too high. Some older houses with a flat section tied into a brick wall have this detail, along with many commercial and multifamily roofs in the area. Once the water is trapped, it can sit against the wall flashing for days.

Winter is the hard season for these outlets. A scupper that drains slowly forms ice at the throat, and water behind that ice has nowhere to go. In St. Louis the freeze-thaw cycle can open small gaps around the box during a cold week, then close them again, and the water works into the gaps each time. After a thaw, look at the outlet. If you see ice at the mouth several days after the last hard freeze, the outlet is still holding water, and the roof above it is taking the load.

Overflow is the backup. An overflow scupper is a second opening set higher than the main outlet. If the main drain clogs, the water rises to the overflow and leaves through it instead of climbing over the parapet or into the wall. Whether a building needs an overflow depends on its design and on the local code, so the permit desk for your municipality or for St. Louis County is the place to confirm the requirement before any contractor cuts a new opening. Do not assume the old opening is correct just because it has carried water until now.

Guards on a scupper are a separate question. A screen over the opening keeps leaves and shingle grit out of the throat, but it also catches debris and holds it against the opening. A screen that clogs with leaves in October can give you the same overflow you were trying to prevent. If you add a guard, check it on the same schedule you check the gutters, and make sure it is fastened to the metal or masonry without pulling the flashing with it. A guard does not make the outlet maintenance-free.

Test the outlet with a garden hose before you decide anything. Ask someone to run water at the far end of the flat section while you watch the scupper. Mark where the water collects and how deep it gets, and photograph the test with a tape or a known object in the frame. Those photos are the record of what the roof did before the work, and they help the contractor who bids the fix decide where the new sill belongs.

What it costs

Scupper work is priced in pieces, and a single line that says scupper hides most of the cost. Look for the opening itself, the cut through masonry or metal, the sheet metal box or liner, the flashing where the box meets the roof membrane, the connection to a downspout or conductor head, and any repair to the parapet cap afterward. A cut through brick takes care, and the mortar patch around the new opening belongs in the bid, not in a later call.

Ask each bid to show the opening size in inches and the sill height above the roof surface. A bid that gives neither number gives you nothing to compare. Two contractors can quote the same opening at different heights, and the lower sill may leave water pooled behind the wall. The price difference is real, and so is the difference in what the roof will do in February.

Keys documents the existing outlet with photos and measurements, and puts a written scope with those photos in your hands before you sign. The scope should list the opening, the metal, the flashing and the downspout connection as separate lines, so the cost of each part is visible. If a bid rolls them into one number, ask for the split before you decide.

Downspout routing matters as much as the opening. A scupper that drops water onto a flat roof edge or a patio with no route gives you a wet wall and a washed-out bed. Extending the discharge to a splash point or into an underground line is a separate item, and the route should be written into the scope with its length and its end point.

What to ask

These questions get you the numbers that decide how the outlet performs in a heavy rain. Ask them of every bid, and keep the answers in writing.

1. What is the opening size in inches, and how high does the sill sit above the roof surface?
2. Is there an overflow opening, and at what height does it sit relative to the main outlet?
3. Who cuts the masonry, and who patches the mortar when the cut is done?
4. What gauge and finish is the scupper box, and how is it sealed to the membrane or the parapet cap?
5. Does the bid include the downspout, the elbow and the discharge point, or only the opening?
6. Does the municipality require a permit or a review for a new or enlarged opening, and who pulls it?
7. Will the outlet be tested with water after the work, and will the result be photographed?

A clear answer on sill height and overflow tells you more about the next heavy rain than a low total on the page. If a contractor cannot give you the sill height, ask for a second visit with a water test before you sign anything.

If you want to talk through an outlet on your own house, call the Keys office at (314) 220-2333. Bring the photos from your hose test and the height you measured at the wall, and ask for the written scope before anything is scheduled.