Ask Habitat: Can We Replace Our Cornice Without Going Broke?

HABITAT ANSWERS: As a rule, the Landmarks Preservation Commission (LPC) prefers that properties in historic districts match the existing materials when doing repairs or replacements. But depending on the particulars of your building, such as the size of the cornice, how ornate it is, the extent of the damage, and the height above street level, your board may be able to replace the cornice with one made out of several LPC-approved materials. The only catch is that the new cornice be an exact visual replica of the original.

If your board decides — or the LPC requires you — to replace your terracotta cornice with terracotta, you should scrape, prime, and paint the reinforcing steel beams (or replace them entirely). Use stainless steel hooks, rods, ties, and anchors, and repair or replace any defective sections of the underlying building wall. If only some sections of the cornice need replacing and other sections patching, a coating can be applied to cover color variations and give the cornice a more uniform appearance, pending LPC approval. The caulking between cornice segments often contains asbestos, so asbestos abatement may be required when removing the existing cornice.

An increasingly popular replacement material for cornices, and one approved by the LPC, is fiberglass reinforced plastic (FRP), a thin shell with an ultraviolet-resistant polyester-gel coating that can be made to match nearly exactly the style, details, and color of the existing cornice.

Even mortar joints, supporting brackets, and other structural elements in the existing cornice can be provided for purely decorative purposes in the FRP mold in the replacement cornice. To an observer looking up from the ground, a well-designed replacement cornice made from FRP is often indistinguishable from one made from the original materials, whether masonry, metal, or wood.

FRP typically comes in sections ranging from two to sixteen feet in length with a shell thickness of roughly three-sixteenths of an inch. The cornice sections are secured to the building using a wood framing and blocking system similar to that used with a metal cornice, and then caulked at the seams and along the edges. Weep holes may be provided along the bottom to allow any water that enters behind the cornice to escape.

The main advantage of FRP is that, unlike terracotta, metal, or wood, it requires very little maintenance because it doesn’t pit, corrode, stain, or fade. In addition, because they are made of a lightweight material, FRP cornices don’t require heavy steel supports or impose structural stresses on the building.

Other materials are sometimes used for cornice replacement. Molds made from glass, fiber-reinforced concrete (GFRC) and Micro-Cotta, a polymer-based composite resin material, can also be fabricated to match the detail and color of an existing cornice.

GFRC replacement segments are typically up to several inches thick, while Micro-Cotta ones are three-quarter inches thick at a minimum. Both materials are lighter than masonry, although not as light as FRP.

Unlike terracotta, stone, or other masonry, FRP, GFRC, and Micro-Cotta are not load-bearing materials, so they can be used only as decorative elements and not in a structural capacity.

For more, see our Site Map or join our Archive >>