Building Codes and Historic Office Corridors
Efforts to accommodate the unique nature of historic features while upholding the safety of occupants and the building itself are increasingly reflected both in newly written rehabilitation codes and how older codes are administered. Traditionally codes have been prescriptive, in that they identify all of the steps necessary to achieve compliance. For example, the code may require that stairways used for egress have a two-hour fire separation and that sprinklers be located at specified intervals.
Standard code requirements, however, do not take into account the individual characteristics of a building and are not easily applied to existing structures.
In addressing these issues, most codes allow authorities to consider alternative approaches often based upon the concept of "equivalency." If existing features are code deficient, architects and building officials may be able to retain them by establishing safety measures that provide an equivalent level of protection to that stated in the code. Fire detection and automatic sprinkler systems, for example, may be expanded beyond minimum code requirements in order to permit the retention of historic features that are not code compliant. This provision is set forth in the National Fire Protection Association's model code for historic structures (NFPA 914) which states, "Nothing in this code shall be intended to prevent the use of systems, methods, or devices of equivalent or superior quality, strength, fire resistance or effectiveness," provided documentation of the equivalency is submitted and accepted by the code authority.
Fire protection options available to those working with historic buildings will expand even further as many states and municipalities incorporate performance-based components into their fire code. Performance-based codes establish life safety goals that fire protection engineers then use to develop a protection plan that is unique to a particular structure. Computer modeling and other forms of analysis allow the engineer to consider every aspect of a building's design, construction and use. Originally developed to give architects additional freedom in designing uncommon building types, performance-based systems are also well suited to assessing and retaining the features of historic buildings.
All fire codes share one primary objective -- to ensure the safe evacuation of a burning building. Because the corridors in high-rise buildings typically function as primary escape routes, fire protection solutions are designed to prevent smoke and flames from spreading through and across the space. Valuable escape and emergency service response time is gained by restricting the rate at which fire and smoke spread. Most prescriptive building codes stipulate a one-hour fire rating for corridors. The wall assemblies separating offices or residences from areas used for public egress must be able to resist heat and maintain their structural integrity for at least one hour during a fire. Door openings that perforate such a wall assembly must have a 20-minute rating. Additional provisions may limit the amount of glazed surface area and the types and characteristics of wall and door glazing.
Although historic masonry walls with two faces of plaster and solid wood doors may meet these basic requirements, most doors, door panels, sidelights and transoms will probably be considered non-conforming elements that require some form of alteration. Such code deficiencies were often corrected in the past by replacing historic doors with solid doors and filling in or removing glazed areas along corridor walls. However, an increasing body of research and precedent indicates that the fire resistance of historic corridor features can be improved with relatively simple modifications that have little impact upon the historic features.
One successful technique developed to upgrade the fire resistance of historic doors and glazed areas is to add sheets of non-combustible material behind the door or glass. The panels, usually gypsum board, calcium silicate board or sheet steel, supplement the inadequate level of protection provided by the original glass or wood panels, thereby achieving the desired rating. If the sidelights or transoms are particularly large, new partitions can be constructed behind the original walls (within the room or office units), again using non-combustible material. Smoke-resistance can be increased by applying intumescent materials such as paint, paste or sealing strips to the space between the edge of the door and the frame. These products expand to several times their original thickness when heated, forming a seal that prevents the passage of smoke and flames. Intumescent stains, clear varnishes and paints can also be used to raise the flamespread resistance of corridor trim and wainscoting.
When major assemblies such as doors and whole wall sections are preserved, a range of other features can also be retained. For example, if historic doors are kept, it is likely that surviving hardware and trim can also be preserved and integrated into the new function. If historic wall assemblies can be modified to meet code, the original dimensions, door locations, trim, flooring and spatial organization of the entire corridor can be retained.
Two structures built in Chicago during the last decade of the 19th century were recently rehabilitated using these approaches to save historic corridor features and meet building and fire code requirements. The Reliance and Fisher buildings, both originally designed by the noted architectural firm Daniel H. Burnham and Company, are important early high-rise office structures and seminal examples of the Chicago School of Architecture. Although the buildings' office spaces were altered over the past century, large portions of the historic corridors survived to the late 1990s when the structures were converted for new uses. The following sections discuss how the corridor features of both buildings were modified for increased fire protection.
