Townhouse Fire Hazards
Life safety hazards must be number one priority regardless of time of day
By Michael Lee
Nearly every department in the United States has some form of multi-family residences in their districts. Fires in townhouses pose a significant challenge from both rescue and fire attack perspectives. Many fires in townhouses are room and contents fires, but it is critical to know how they may impact your own responses and how quickly fire can spread in these types of residences.
Townhouses are constructed in numerous architectural and floor plan designs, varying greatly in age and construction. They are labeled by a variety of titles based on geographic culture and if the unit is a rental or owned. The number of units in a building may also be used to title a specific style of townhouse.
Some examples include:
- Townhouse: One to four story units normally attached to several other units.
- Duplex: Two dwelling units connected together under a single roof.
- Quad: Four dwelling units connected together back to back under a common roof with separate addresses and separate entrances.
- Piggybacks: Two stacked units (one over the other) with attached units on each side, each with a separate address and entrance.
Townhouse construction is typically type V, wood frame, platform construction. Roof frames are either lightweight truss construction or conventional with sawn rafters depending on their age. Both types of roof support generally have a 4x8 plywood or OSB sheeting decking.
While numerous styles of roof construction exist on current townhouses, the roof is generally pitched from the center peak to the front and rear; occasionally a perpendicular gable may be found in the front. The presence of a dormer may not necessarily indicate a finished attic as it may be false and/or architectural.
A very dangerous style of roof for firefighters responding to fires is the mansard-style roof. Mansard roofs wrap around exterior division walls, allowing fire to spread in the cockloft. All townhouse fires can allow fires from windows to extend from the primary fire unit into common attic areas. This should prompt crews to open the ceiling above them prior to entry into units to ensure they are not advancing into a structure with an unknown fire overhead eating away at the chords of a truss supporting overhead weight.
Some older townhouses have usable attics. Attics, if present, may be unfinished and possibly used for storage by residents. Attic access may be through a scuttle or pull-down stairs on the top floor, and may be located inside a closet or bathroom. Construction in attics to create livable space will generally create half or knee walls, which can present hidden areas for fire to hide.
Firewall construction will generally run from the ground floor to above the roof line. It may be placed in a variety of areas including between each unit, between every other unit or between the living spaces (occupied floors) that do not extend into the attic or basement.
Newer performance-based codes allow for firewalls to consist of substantial drywall (2" or greater) that will serve as a firewall, thereby reducing the overall square footage in a unit. This in turn can mean that square footage is reduced to the point where sprinkler requirements are not required by local code.
Firewall construction may consist of masonry, 1-inch gypsum layered on both sides of a common wall, or offsetting ridgelines or rooflines with gypsum board separation. Exterior doors may be constructed of solid wood, insulated metal, or wood panel.
Townhouses may have a garage on the lowest level or detached in a common alley, and can even have unfinished basements allowing for fire spread to other structural components.
One of the most critical features in townhouses is the open central stairway, which allow for rapid spread of fire and combustion products. Common stairway construction features within a construction project may both help or hinder firefighting tactics. These features consist of stairways that are commonly stacked within the same area of the building and are generally on a connecting wall. These stairways will require an attack line to preserve egress avenues and firefighters should remember that fire may exist underneath them in a lower stairway.
Life Safety Hazards
Life safety hazards must be our number one priority regardless of the time of day. Townhouses have a significant life hazard as numerous occupants will have a variety of schedules throughout the day and night. In addition to the typical egress paths (windows, doors and hallways) that fire can spread through, occupants in attached exposures present additional life hazards.
Smoke from an adjacent unit may be forced into lateral units through common voids and the positive pressure generated from the fire. In addition, some cultures believe in keeping their family units together in one townhouse, which means 15-plus family members may be contained in just one residence. Also keep in mind that sub-leasing may create an additional life hazard as both basement and sub-basement areas may have been converted to sleeping areas.
Interior void spaces in addition to horizontal and vertical openings allow smoke and fire spread and will necessitate the opening of walls and floors. With the increase of lightweight construction and use of truss systems, common void spaces will exist between each floor and the ceiling above and in the attic as well.
Combustible siding can extend exterior fires up into the attic and roof areas. In addition, fire can spread through wet walls where plumbing, HVAC and electrical wiring are run. Fire can spread to adjoining areas through penetrations in the firewall or by bypassing it.
Lightweight construction is prevalent in most townhouse construction: Beware of collapsing truss roof members on the top floor from an attic fire or top floor fire. Fire in an unfinished basement could expose and weaken structural members.
Occupants that have added significant live load to the floors — such as waterbeds — could accelerate the potential for collapse truss-based construction. Fire in a floor void (open-web, parallel chord truss) could jeopardize structural integrity prematurely.
Beware of the installation of suspended ceilings in commercial occupancies that create combustible void spaces that may spread fire laterally, causing it to out flank suppression crews. In addition, masonry veneer walls can fall straight outward and strike the ground.
A further hazard can be found with overhead garage doors that can entrap suppression crews during a working garage fire — door springs and/or chain motor may fail. You should support garage doors with pike poles, a frame ladder or modified vice-grips.
In next month's column I will focus on how to respond to townhouse fires.
- Fire Attack