By: Kevin Duffy
If you walk through the streets of New York City, cornices are some of the most prevalent architectural features you will see. They come in a variety of shapes and sizes. They can be made of sheet metal, wood, terra cotta, or architectural pre-cast concrete. Some cornices are made of fiber reinforced polymer (FRP), which is also referred to as glass fiber reinforced polymer (GFRP), or more commonly Fiberglass. Due to the relatively labor intensive installation process, very few wood or sheet metal cornices are currently being installed or repaired.
For years terra cotta was the most prevalent cornice material; however, fiberglass is now becoming a more popular option in the exterior restoration business for several reasons. Terra cotta is notoriously difficult to inspect and preserve due to its hollow nature and complex construction process. Itas often difficult to determine whether water, which could cause spalling during the next freeze thaw cycle, might be trapped inside. It is also difficult to determine if the steel structures supporting the terra cotta are corroded. A fiberglass cornice system is much easer to inspect since the fiberglass itself rarely deteriorates. Any system fails is usually at the sealant joints between the fiberglass pieces, which is easily repaired.
Fiberglass is significantly lighter than terra cotta. Terra cotta weighs approximately 122 pounds per cubic foot, which is only slightly less than structural concrete. To circumvent itas weight, terra cotta was often manufactured to be hollow. However, some cornices can extend out up to 6a from the face of the building, creating a large load (or moment) on a parapet wall, irregardless that the terra cotta is hollow. This downside to terra cotta is also the same if pre-cast concrete were used. Fiberglas cornices are typically about 1/8a or 3/16a thick and installed on steel framing that is mounted onto the parapet wall.A This steel framing is often spaced farther apart than it would be in a terra cotta or pre-cast concrete cornice.
The cost effectiveness of using fiber reinforced polymer for a cornice replacement is another advantage. Only 2 companies in the United States: Boston Valley Terra Cotta in Orchard Park, NY and Gladding, McBean in Lincoln, California, manufacture architectural terra cotta. Relatively long distances, coupled with the weight of the material, can lead to high shipping costs. Although there are only 2 manufacturers of architectural fiberglass servicing New York City, both Seal Fiberglass and Architectural Fiberglass Corp. are located less than 11/2 hours from downtown Manhattan.
Shorter lead-time is another advantage to installing FRP cornices. A full-scale terra cotta project can take up to 24 months for production to complete, while fiberglass is often a fraction of the time, depending on how ornate the building is.
Since fiberglass does not weather like pre-cast concrete or terra cotta, some say it sometimes looks fake or even cheap. This aesthetic criticism is waning however as more advanced fabrication techniques are used in the manufacturing process. Even the New York City Landmarks Preservation Commission has recently started to approve FRP cornices on landmark buildings, provided the color matches are close.
While there is no perfect cornice replacement option, FRP is certainly a solid choice (no pun intended). If you suspect your cornice might need to be repaired or replaced, you should contact a professional engineer or registered architect that is familiar with inspecting cornices.