What is a cornice?

A cornice is projecting decorative trim that crowns a building or wall. Exterior cornices also help direct rainwater away from the building face.

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By InstaBids editorial team with AI research agents. Updated 30 October 2026

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What is the purpose of a cornice?

An exterior cornice helps shed rainwater away from the building face. Saint Paul’s design guidance describes this practical purpose for projecting cornices. “Cornices are projections from buildings that help to keep rainwater away from the front of the structure.” Source: City of Saint Paul, read 2026-10-30.

What is the architectural definition of a cornice?

A cornice is projecting decorative trim at the top of a building or wall. Monticello’s architectural glossary also includes trim that crowns an arch. “Any projecting ornamental molding that finishes or crowns the top of a building, wall, or arch.” Source: City of Monticello, Illinois, read 2026-10-30.

What materials are cornices made from?

Cornice materials depend on the setting. Philadelphia’s historic exterior examples include wood, sheet metal, cast iron and copper; historic interior plaster cornices can contain gypsum and lime. “Cornices are usually constructed of wood or sheet metal, although there are cornices of cast iron, and copper throughout Philadelphia.” Source: Philadelphia Historical Commission, read 2026-10-30. “For example, an elaborate parlor cornice consisted of plain moldings made of gypsum and lime run atop temporary lattice strips around the room.” Source: National Park Service, read 2026-10-30.

What is a cornice return?

A cornice return is the part of the roof-edge cornice that continues onto the gable end of a house, as the federal housing glossary explains. “That portion of the cornice that returns on the gable end of a house.” Source: U.S. Department of Agriculture, read 2026-10-30.

Why is my cornice cracking?

Movement and settling can crack historic plaster cornices. The National Park Service also identifies roof or plumbing leaks as causes of peeling, discoloration and salt deposits on cornices. “Buildings move and settle, causing deflection and delamination which result in stress cracking.” Source: National Park Service, read 2026-10-30. “Roof or plumbing leaks make finishes discolor and peel and cause efflorescence, especially on plain-run or enriched cornices.” Source: National Park Service, read 2026-10-30.

Sources

Glossary of Architectural Terms — City of Monticello, Illinois; read 2026-10-30.
District 9 Area Plan Summary: Cornices, page 14 — City of Saint Paul; published 2013; read 2026-10-30.
Historic district maintenance manual: Cornices, page 9 — Philadelphia Historical Commission; read 2026-10-30.
Glossary of Housing Terms: Cornice return, page 88 — U.S. Department of Agriculture; read 2026-10-30.
Preservation Brief 23: Preserving Historic Ornamental Plaster — National Park Service; read 2026-10-30.