Almost all of us have this one fire problem in common: the 1½ to 2½-story dwelling and the challenges it presents. These structures are usually single-family dwellings, but some of the larger 2½-story structures may be renovated into two- or three-family dwellings.
One specific challenge these structures present is the knee wall, a confined space in the half-story above the tallest full story. The half-story can be finished with either drywall or lath and plaster, depending on the age of the structure, and used for living space or storage.
The knee wall is a vertical wall that stretches about 3—4 feet internally from the floor toward the peak of the roof. A concealed space is created behind the knee wall and usually extends to the eaves; it may be used for storage space or as a means to conceal plumbing or electrical wiring, which will increase the risk of extension.
Size-Up & Balloon Construction
A thorough and accurate size-up will greatly increase your chances for success when fighting a fire in a structure with knee walls and concealed spaces, because it will help you determine many important aspects of the structure, such as the type of building construction, the height of the building and the location and extent of the fire. These elements should give you clues as to the possible presence of knee walls and the aggressive measures that you’ll need to take to confine and extinguish the fire.
Often, these buildings are wood-frame construction, but depending on the building’s age, they may also be balloon-frame construction. If you identify balloon construction, stretch handlines to all floors of the building. The truck company will also need to prepare for aggressive roof ventilation.
If the fire penetrates the wall space of the balloon-frame construction, all wall spaces on each floor will need to be opened from floor to ceiling and an engine company will need to work in conjunction with the truck company, with a charged line at the ready.
Hoseline Placement & Fire Attack
The interior will vary within these structures, but for the typical 1½-story, single-family dwelling or Cape Cod-style home, the interior stairs will be close to the front door. The bedrooms are likely to be located on both floors of the home, with one or two on each floor. With this layout, hoselines should initially be positioned to protect the stairs and any occupants, with at least one hoseline between the fire and the occupants.
The second line must serve as a back-up line to the initial-attack line. If you determine that the initial-attack line has the fire controlled, the back-up line can then be repositioned above the fire. As soon as the initial-attack lines knock down the fire, the ceiling and outer wall spaces must be opened up and the line operated in the void space. If the back-up line must stay in place, a third line must be stretched above the fire as soon as possible.
If the fire has penetrated the concealed space in the knee wall, the company stretching the hoseline to the second floor will typically encounter high heat conditions when reaching the top of the steps. The attack line to the floor above must be charged prior to ascending the steps. In a typical Cape Cod-style house, the firefighters on the attack line will have the option of going to the right or left at the top of the stairs. The line should obviously go in the direction of the fire below. Tip: Use a thermal imaging camera when determining where to place the line and the presence of fire in the concealed space.
If the fire is not immediately visible on the upper floor, the truck company needs to begin opening up the knee wall above the fire. The engine company must also be ready to open its line as soon as the space is opened. If a truck company is not available, the engine company must take tools with them when they advance the line up the stairs. Tip: Due to the limited workspace, use an axe, a short pike pole or a Halligan bar.
As crews open the knee wall and encounter fire, they must aggressively open the hoseline in the concealed space. An additional hoseline should also be considered and advanced up the stairs and stretched in the opposite direction as the initial line above the fire. The company operating the second attack line above the fire should then open the knee wall on the opposite side of the steps and prevent the fire from spreading behind the initial line.
Remember: It’s not unusual to require more than one line in fires involving knee walls. So if any doubt exists as to the extension of the fire into the knee wall, it’s always good practice to open it up!
Triangles & Dormers
If fire is located in the knee wall, it’s a good idea to open the ceiling directly at the peak of the roof. Many finished half-stories will have a small, triangle-shaped, concealed space at the peak. This area is connected to the knee wall by the rafter construction and there are rarely any inherent fire stops.
Often, residents remodel their half-story and add a dormer. A dormer will extend along the roofline, providing additional living space, and as a result, often eliminates the knee wall on that side of the structure. However, although the knee wall is eliminated, the dormer still presents concealed spaces for fire to travel and therefore must be aggressively opened. Dormers are often added to provide room for an additional bathroom on the second floor. The plumbing may provide an additional path for fire travel.
Things to Remember
The keys to combating a fire in structures with knee walls: 1) aggressive truck work on the fire floor and the floor above, and 2) the timely advancement of hoselines on the fire floor and the floor above. Operating hoselines into the concealed spaces may be the key to saving the roof.
Most importantly, if in doubt about fire spread, don’t hesitate to open up the knee wall.
