Metal Coping: Caps for Parapet Walls, Explained

Metal coping is a sheet-metal cap that covers the top of a parapet wall, the short wall that rises above a flat or low-slope roof. It sheds water off the wall top, protects the roof membrane where it turns up the parapet, and finishes the edge of the building. Coping is also used on garden walls and on modern houses with flat roofs. When it fails, water goes straight down into the wall, so the details matter more than the metal.

Anatomy of a coping

• Top (cap): slopes slightly, usually toward the roof side so dirty water doesn't stain the face of the building.
• Legs: come down both sides of the wall, ending in a hemmed drip edge held away from the wall so water drips off instead of running down it.
• Cleats: continuous metal strips fastened to the wall (or to a wood nailer on top of it) on each side. The coping's hemmed edges hook onto them. Cleats hold the coping down in wind without exposed fasteners on the face.
• Joint covers (splice plates): short pieces under or over the joints between coping sections, set in sealant, so sections can expand and contract.
• Underlayment: a self-adhered membrane over the wall top, under the coping, as a second line of defense.

Slope and drip

A flat coping holds water at the joints. Build the slope into the wood nailer or blocking underneath, sloping toward the roof. Make the outside leg long enough to lap well below the top of the wall, a few inches on most buildings, and keep the drip edge off the wall face.

Joints and expansion

Metal moves a lot with temperature. Coping is usually installed in 10- or 12-foot sections with a gap of about 1/4 inch at each joint, bridged by a splice plate set in sealant. Corners are made as one welded or soldered piece. Rigid, caulked-only joints crack open within a few seasons.

Materials

Material	Typical thickness	Notes
Prepainted steel (Galvalume or galvanized)	24 gauge	Most common; matches roof edge metal
Aluminum	0.050 or 0.063 inch	Doesn't rust; painted finishes; good near the coast
Stainless steel	24 to 26 gauge	Long life; higher cost
Copper	16 or 20 oz	Historic and high-end buildings; stains masonry below

Wind and code

On commercial buildings, the International Building Code requires low-slope roof edge metal, including copings, to resist wind. That's usually met by systems tested to the ANSI/SPRI/FM 4435/ES-1 standard. Manufactured coping systems come with test data, which is one reason commercial roofers buy them instead of bending their own. On houses, follow the roofing manufacturer's edge details.

How coping connects to the roof

The roof membrane runs up the inside of the parapet and over the top of the wall before the coping goes on, or it ends on the inside face under a termination bar with counterflashing above. Where the parapet is masonry and the coping doesn't cover the membrane edge, a reglet flashing does the job.

Common problems

• Coping that slopes outward and streaks the facade
• Face-nailed coping that pulls loose in wind
• No underlayment, so every joint leak soaks the wall
• Sealant-only joints that crack
• Short legs that let wind-driven rain under the coping