By Jerry R. Tindal, M.S.M.E., P.E., CFEI
Attic fires can be one of the most destructive and dangerous types of fires. This is particularly true when attic and roof structures are of wood framed and sheathed construction. Because wood is readily available, easy to use, and economical, there are a large number of buildings that use wood framing and sheathing in attic and roof construction. Unfortunately, most of these attics contain no automatic sprinklers, smoke or heat detectors, and subsequently early detection and suppression of attic fires can be a problem. In addition, attic fires are usually difficult and dangerous to fight due to their confined nature. These unique problems typically result in the total destruction or substantial damages to the structure.
Building codes and local ordinances prescribe the type of fire protection required in attics. Local ordinances requiring automatic sprinkler protection throughout buildings, including attics are in place in a few jurisdictions in the United States. These types of ordinances are gaining popularity and the result is a substantial decrease in property losses due to fires in these jurisdictions. However, these ordinances do not exist in most local jurisdictions throughout the United States. Most jurisdictions use building codes, which gauge the requirements of sprinklers on the size and construction types of the building and contents contained in the building. However, the sizes of buildings that can be constructed today without sprinklers can equate to a sizable dollar loss in the event of a fire.
Two of the most common commercial building types using wood frame construction in the attic and roof are apartment and motel structures. In some building codes these structures can be constructed two stories with as much as 14,000 square feet per story without any sprinkler protection. This generates a lot of attic space! The codes however do provide a significant feature to limit fire spread in attics. Provisions for draftstopping have been included in the building codes for more than thirty years.
Draftstops are an easy to install, economical and a highly effective means of slowing the spread of fires in attics. Draftstops are vertical barriers, most typically constructed out of a single layer of ½" gypsum board, that subdivide attic areas into smaller areas. The intent is to slow or prevent the fire from "sweeping" through and involving the entire attic and ultimately the living areas below when the ceilings collapse. Slowing the fire spread in the attic buys valuable time for firefighters to control the fire before it spreads extensively through the building. Unfortunately, many architects, contractors and owners omit draftstops in attic spaces during construction for "time and economic reasons" or because they lack knowledge of the codes. This folly is particularly problematic in older buildings although it occurs occasionally in new construction.
In multifamily dwelling units (apartments), motels and hotels, the codes require draftstopping "in the attic, mansard, overhang, or other concealed roof space above and in line with tenant separation when tenant separation walls do not extend to the roof sheathing above" and in other buildings "in attic spaces so that horizontal areas do not exceed 3,000 square feet". Note that, as always, exceptions exist for certain circumstances. When draftstops are properly installed attic fires will be slowed providing time for occupants to escape and firefighters to gain control. When they are not installed the potential for serious injury, death or substantial property damage increases significantly with attic fires.
It is important to ensure proper draftstops have been installed, where required by code, in all new and existing structures of wood frame construction to help mitigate the potential for injury and property damage in the event of a fire. If a fire occurs in one of these structures it is usually not difficult to tell if proper draftstopping was in place in the attic, provided enough of the building remains. First, look for areas in the attic where a sharp contrast in fire damage exists. This will usually occur along a well-defined straight line with little to no damage on one side and heavy damage on the other. Next look at the side surfaces of the wood structural members making up the trusses along the line. Roofing nails with large flat heads that were used to secure the draftstop partitions to the sides of the trusses will remain after the fire. Finally, there may be obvious remains of sections of the draftstop on portions of the trusses.
One of the best indications that draftstopping was not present is the "rapid" and complete destruction of the attic and roof. In order to qualify that determination however a comprehensive analysis of the circumstances surrounding the fire is required. A time line analysis of the discovery, report and suppression activities of the fire would be beneficial in such an analysis. The interview of witnesses, fire fighters and building maintenance personnel or owners would also provide valuable information. If plans of the structure are available they can be reviewed to determine if draftstopping was included in the design. Finally, check building and fire inspection records with state or local authorities.
National Fire Protection Association (NFPA) 921 Guide for Fire and Explosion Investigations, 2001 Edition 16.1 indicates that fire investigations should include consideration of the cause of damage to property resulting from a fire. This particular feature includes factors responsible for the spread of fire. As such fire investigators must be cognizant of building construction features that help limit or control the spread of fire. More importantly the fire investigator should question and investigate when these features were not present but were supposed to be.
The engineers at The Warren Group are experienced in analyzing fire causes and are familiar with code provisions that should limit or control the spread of fires. These considerations are always kept in mind during the investigation of any fire. If you have any questions or we can be of assistance please give us a call.