Replacing a Cornice

The original terra cotta cornice on our Park Slope cooperative has steadily deteriorated. (It’s more than 100 years old.) Over the past few years, we’ve patched the particularly bad spots, but we’re now at a point where we’ll probably have to replace some sections of the cornice and possibly the entire thing. We would like to replace it with terra cotta and maintain the cornice’s decorative features as much as possible, but the costs may be beyond our budget. We’re told that there are replacement materials available, but because our building is in a historic district, we may be limited to what types we can use. What are our options for a cornice replacement that meets the Landmarks Preservation Commission’s approval yet is still relatively affordable?

Although cornices serve a waterproofing function by shielding the top of the building’s façade from rain runoff, their purpose is chiefly decorative. For conscientious building owners who want to preserve the architectural qualities and historical character of their properties, keeping the cornice in sound condition is of paramount importance.

Because your building is located in a New York City-designated historic district, your options for repairing and/or replacing the cornice are established by the Landmarks Preservation Commission (LPC). While the LPC requires a replacement cornice to match the appearance of the existing one, it does provide leeway regarding the type of replacement material that can be used.

Cornice Types. Traditionally, cornices were commonly constructed from either masonry (terra cotta or stone), sheet metal (usually galvanized steel or sometimes copper), or, for some older buildings, wood. Terra cotta cornices such as the one on your building are solid structures supported by steel beams, hooks, and anchors embedded into the building and the cornice itself. Metal cornices are secured to the building with steel or wood framing and blocking. Wood cornices consist of an overhang or “shelf” supported by decorative brackets bolted directly into the façade. Cornices can extend several inches to three or four feet from the building.

When considering whether to repair or replace your cornice, the first step is to have an engineer or architect perform a hands-on evaluation and investigative probing from a scaffold. The engineer or architect will assess the condition of the terra cotta and the underlying support framing. The evaluation will help determine whether the cornice can be patched or repaired in places, or if sections or the entire cornice needs replacement. Metal cornices should be checked for rust, corrosion, and deflection. Wood cornices should be similarly inspected for rotting, cracking, and splitting.

If the cornice is badly deteriorated, sections of it may need to be removed so the condition of the backup wall can be inspected. Chances are that water has penetrated into or behind the cornice causing damage to the wall as well. Before a new cornice can be installed, the wall may need repointing or need 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. Attaching a new cornice to a defective wall will only compromise the installation and perpetuate water infiltration.

If it is determined that the entire cornice or main sections of it need repair or replacement, then your board has several options, all of which are subject to LPC approval. As a rule, the commission prefers that properties in historic districts repair or replace bricks, stone, masonry, cornices, and decorative elements with materials the same as the existing ones. 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. But the new cornice must be an exact visual replica of the original.

If your board decides – or the LPC requires you – to replace your terra cotta cornice with terra cotta, several steps are recommended. The reinforcing steel beams should be scraped, primed, and painted, or replaced if necessary. New stainless steel hooks, rods, ties, and anchors should be used, and any defective sections of the underlying building wall will have to be repaired or replaced. 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.

Fiberglass-reinforced plastic cornices. 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 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 terra cotta, 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. They are also much cheaper to manufacture and install than terra cotta or metal, approximately $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 typically come with a 10-year warranty.

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 terra cotta, 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.

Keep in mind that the installation of a replacement cornice must be integral with the building and its structural supports; it can’t just be slapped up on the side of the wall. The top surface of the cornice should be pitched slightly away from the building so water runs off the edge and not back toward the joint between the cornice and the building wall. Depending on the cornice design, counterflashing installed over the top lip of the new cornice may be recommended to further prevent water penetration. Replacing sections of the cornice with different materials (such as terra cotta and FRP), even if they match visually, can lead to problems resulting from the materials’ different expansion and contraction properties and attachment details.

Regardless of the type of material your board decides to use, there are a few considerations to be aware of with any cornice replacement program. First, consider the timeline: for landmark properties or buildings in historic districts, the LPC can take anywhere from several weeks to several months to review and approve the design for the replacement cornice.

Fabricating replacement segments can take three to four months from the time the manufacturer’s shop drawings are approved, and shop drawings themselves can take about four to six weeks to prepare. Add the time for the engineer’s or architect’s initial evaluation, preparation of bid documents, bid solicitation, contract award, LPC and DOB permits, and installation, and a cornice replacement project could take four to eight months from start to finish. Sometimes a cornice replacement project is coupled with a roof replacement program because some cornices are integrated into the roof deck.

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) to iron out the attachment details and specifics of the building, placing the full responsibility for proper manufacture and installation on the contractor.

Whether your board ends up repairing its cornice or replacing it with terra cotta or an LPC-approved substitute material, the important thing is that you will be retaining your building’s unique characteristics and character for years to come.