Raised floor systems are an increasingly important component of green building design. One benefit is flexible wire and cable pathways, often including modular manufactured wiring systems. Another plus for raised floors is underfloor HVAC distribution that provides consistent temperature, ventilation, humidification, and air quality throughout the facility. However, co-locating wiring and air handling requires that special attention be paid to the raised floor boxes that provide power, voice, data, and video. There is also considerable confusion about terms such as "plenum" and "environmental air spaces" in raised floor applications. The use and definition of the word "plenum" as it applies to raised floors varies widely within the industry. Because its interpretation is very important in specifying raised floor products, such as floor boxes and manufactured wiring systems, confusion can be significantly reduced by understanding the definitions used by UL and the National Electrical Code.