"Large open attic spaces generally occur as the result of an architectural decision to have a tall roof line on a building. Often, these spaces are unheated, have limited ventilation, marginal access, and no fire protection because they are not meant to be occupied spaces. The structural supports may be there solely to support the roof and ceiling elements, and may not be capable of handling additional loads. Almost as often, however, this unused space provides the building tenant a simple solution to storage problems. Whether the storage occurs in the attic of a multi-family dwelling, the weather-resistant crawl space of an office occupancy, or in some other concealed space, there is a potential for combustible storage to add to a building's fire load and weaken its structural integrity."
Coffee Break Training - Fire Protection Series No. FP-2010-5
United States Fire Administration: http://www.usfa.fema.gov/