Parapet wall and coping repair in Washington, DC

Most rowhouses have a parapet across the front, often finished with a decorative cornice, and lower parapets along the party walls and the rear. They hide the flat roof from the street, act as a fire separation between houses and give the roof membrane something to turn up against.

Because a parapet is exposed on both faces and the top, it soaks up more rain than any other part of the wall. Water that gets into the top courses moves down through the brick by gravity, passes the roof line and appears inside as peeling paint, damp plaster or efflorescence high on the wall.

The top of the wall is protected by coping, which on older rowhouses might be stone, terra cotta, brick laid on edge, a mortar wash or sheet metal. Each type fails in its own way, and the repair has to suit what is there and, on a visible front, what the block looks like.

Metal coping is the most common fix on rowhouse rear and party walls today. A properly installed metal cap slopes toward the roof, has drip edges on both faces, sits on cleats rather than being nailed through the top, and has joints that allow the metal to expand. Old caps often fail at the joints, where sealant has cracked and water runs into the wall at every seam.

Stone and terra cotta copings fail when their mortar joints open or when units crack and rock loose. We reset loose units on fresh mortar, rake and repoint open joints, and replace broken pieces where the original material is still available. Where it is not, a metal cap over the existing coping is a practical fix for walls out of sight of the street.

Brick-on-edge caps with no separate coping are the hardest to keep dry. They nearly always need either a metal cap or a full rebuild of the top courses with a through-wall flashing beneath.

A through-wall flashing is a sheet of metal or flexible flashing that runs completely through the parapet a few courses below the coping, turned up on the inside and with a drip on the outside. It catches water that gets past the cap and sends it out of the wall before it reaches the roof line.

Most older DC parapets were built without one. When we rebuild the top of a parapet, we add a through-wall flashing and weeps, which does more to stop chronic leaks than any amount of sealer on the brick face. This work sits right where masonry and roofing meet, and we handle both sides of it.

For walls that only need repointing, we use a mortar compatible with soft historic brick. Hard modern mortar on old brick traps water and spalls the brick faces, which we see on many parapets that were repointed in the past few decades with the wrong mix.

The roof membrane must turn up the inside face of the parapet, usually eight inches or more, and be capped by the coping or by counterflashing let into a mortar joint. On many rowhouses the membrane stops short or is held only by roof cement along the brick, and that is where the leak starts.

Some roofers wrap the membrane all the way up and over the top of a low parapet, under the coping. That can work well on rear and party walls if the membrane is fully adhered and the coping goes back on top. We pick the detail that suits the wall height and condition. Our page on flat roof repair covers the field of the roof itself.

Front parapets often carry a pressed metal or wood cornice that belongs to the character of the block. In historic districts such as Shaw, LeDroit Park and Mount Pleasant, changes to a visible front can need Historic Preservation Office approval. We keep repairs like-for-like: matched brick, compatible mortar and metal profiles that follow the original.

Cornice repairs often happen at the same time as parapet work, because the cornice hangs from the parapet and drains into the box gutter behind it. When the cornice metal is rusted through, we patch or replace sections and connect it to our box gutter repair so the whole front sheds water together.

Party wall parapets bring a neighbor into the picture. A wall shared by two houses is usually a shared responsibility, and we are happy to show both owners the photos and walk the wall with them before any work begins.