Parapet wall leaks on Jersey City rowhouses

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What a parapet is

A parapet is the part of a wall that rises above the roof. On a row, the front wall usually rises behind the cornice, the rear wall rises at the back, and low dividing walls may separate your roof from your neighbors’. The flat roof sits inside these walls like the floor of a shallow box. That box keeps water on the roof until it drains, which is exactly why every joint around it matters.

The three ways water gets in

Through the top: the coping

The coping is the cap along the top of the parapet, often stone, terra cotta or metal. Its joints and its seal to the brick keep rain from soaking straight down into the wall. When those joints open, water enters at the top and runs down inside the masonry, sometimes for a long way, before it shows on a ceiling or a wall below.

Through the face: the brick and mortar

A parapet is exposed on both sides and on top, so it takes more weather than the walls below it. Mortar joints wear, bricks crack, and freeze and thaw over the winter opens small gaps wider. Wind-driven rain then pushes water into the wall from the outside face or the roof side.

Through the base: the flashing

Where the flat roof meets the parapet, the roof covering turns up the wall and is protected by flashing. If that flashing loosens, cracks or was never tucked in properly, water standing on the roof or running down the wall gets behind the covering and into the building.

Scuppers through the wall

Many rows drain through a scupper, an opening cut through the parapet that lets water spill to a leader or off the roof. The scupper is a hole in the wall by design, so its lining and flashing have to be sound. A scupper clogged with leaves or ice also makes water pond against the parapet, which tests every joint around it.

Signs you can see

• Damp or stained plaster near the top of a side or front wall, often worse after wind-driven rain
• Peeling paint or a white powdery bloom on the inside of an exterior wall
• From the hatch: coping pieces that look loose, open joints, or plants growing from the wall top
• Flashing at the foot of the parapet that has pulled away or split
• Water standing against the parapet after rain

Look from the hatch or a window, and photograph what you see. Stay off the roof when it is wet or icy.

What a roofer looks at

A roofer called about a parapet leak should look at all three paths, not just the flashing. Expect them to check the coping joints and the seal to the brick, the condition of the brick and mortar on both faces, the flashing along the base, and every scupper and drain nearby. Some parapet problems are masonry work; ask whether the roofer handles that or works alongside a mason. The guide to roof repair in Jersey City covers the usual repairs, and roof leak repair explains how leaks are traced.

The front parapet and the cornice

At the front, the parapet often sits right behind the cornice, and water that gets into one can affect the other. Parts of Downtown, such as Paulus Hook and Van Vorst Park, are historic districts: ask the city before changing roofing material or anything visible from the street. See brownstone roof repair and the article on roof work in a historic district.

The shared parapet

A dividing parapet between two rowhouses belongs, in effect, to both roofs. A leak at that wall may start on your side or your neighbor’s. Ask the roofer to look at both faces if they can, and talk with your neighbor. Repairs to a shared wall go better when both owners know what is planned.