Replacing a Cornice is No Easy Task

Traditionally, cornices were constructed from either masonry (terra cotta or stone), sheet metal (galvanized steel or sometimes copper), or wood. Terra cotta cornices are solid structures supported by steel beams, hooks and anchors. Metal cornices are secured to the building with steel or wood framing and blocking. Wood cornices consist of an overhang supported by decorative brackets bolted directly into the façade.

Whether repairing or replacing your cornice, the first step is to have an engineer or architect perform a hands-on evaluation and probe from a scaffold. This will help determine whether the cornice can be patched or repaired in places, or if sections or the entire cornice needs replacing. Chances are that water has penetrated into or behind the cornice, so the wall may need repointing or to have some bricks replaced to make it watertight and structurally stable. In some cases, installing a new waterproofing membrane or applying a cement coating may be necessary. You might also need counterflashing installed over the top lip of the new cornice to further prevent water penetration.

The Landmarks Preservation Commission (LPC) prefers but does not require that buildings repair or replace materials with like materials. The important thing is that the new cornice must be an exact visual replica of the original.

Replacing sections of the cornice with different materials, however, even if they match visually, can lead to problems resulting from the materials' different expansion and contraction properties and attachment details.

Nuts and bolts

To replace terra cotta with terra cotta, the reinforcing steel beams should be scraped, primed and painted, or, if necessary, replaced. New stainless steel hooks, rods, ties and anchors should be used, and any defective sections of the underlying building wall must be repaired or replaced. The caulking between cornice segments often contains asbestos, so asbestos abatement may be required when removing the existing cornice.

An increasingly popular choice of 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 molded and colored to match the style, details and color of the existing cornice. Viewed from the ground, a well-designed replacement cornice made from FRP is often indistinguishable from one made from the original materials.

FRP typically comes in sections ranging from two to 16 feet in length, with a shell thickness of roughly 3/16 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.

FRP, unlike terra cotta, metal or wood, requires little maintenance because it doesn't pit, corrode, stain or fade. It's lightweight, so FRP cornices don't require heavy steel supports or impose structural stresses on the building. They're also much cheaper to manufacture and install than metal or terra cotta — about $1,000 a linear foot compared to $1,200 for metal and several thousand dollars for terra cotta. (Wood cornices are typically handcrafted, which adds to the time and cost of building one.) FRP cornices generally have 10-year warranties.

Other materials sometimes used for cornice replacement include glass, fiber-reinforced concrete (GFRC) and the trademarked brand Micro-Cotta, a polymer-based composite resin. Each is lighter than masonry, although not as light as FRP. NOTE: FRP, GFRC and Micro-Cotta, unlike terra cotta or other masonry, are not load-bearing, so they can be used only as decorative elements and not in a structural capacity.

To avoid a contractor's markup, some boards buy a cornice directly from a manufacturer and then hire an exterior restoration contractor to install it. This approach, however, can lead to problems during installation if the manufacturer's design, done without the input of a contractor at the job site, does not exactly match the field conditions at the building. Better to have the contractor work directly with the manufacturer with your engineer or architect consulting.

The LPC can take from several weeks to several months to review and approve the design. Shop drawings can take about four to six weeks to prepare, and fabricating replacement segments can take three to four months. Add the time for the engineer's or architect's initial evaluation, preparation of bid documents, bid solicitation, contract award, LPC and Department of Buildings permits and installation, and a cornice replacement could take four to eight months from start to finish.

Whether you end up repairing or replacing your cornice, and with whatever material, the important thing is that you'll be retaining your building's unique characteristics and character for years to come.

Stephen Varone and Peter Varsalona are principals at Rand Engineering & Architecture.

Adapted from Habitat April 2008. For the complete article and more, join our Archive >>