The Case For The Half -Story In Your Size-Up
Painting an accurate picture of what the first arriving fire unit encounters is vital when giving an initial fire scene size up. Being able to clearly and efficiently communicate the current situation to other responding units is a good first step in working towards a successful outcome at an emergency.
What we should also do though, is communicate this in terms that make sense to other units so they can begin to formulate a pre-arrival plan in order to work more efficiently and effectively.
One way to do this, is to understand the importance of stating the half story in your size up, when a peaked roof is encountered.
Where I work, a large part of our housing stock is either two and a half story, or three story wood framed multi-family housing. There is no consistency or pattern as to where one roof type will be encountered over another in a given street or neighborhood.
So for us, announcing the half story gives incoming units valuable information that allows them to get a clearer picture of the situation, and better prepares them for the tasks at hand. When talking to firefighters about size up, I often hear folks take a very code related approach, and argue what a half story is or is not, based on their interpretation of the local building or fire codes.
Some folks will describe the structure as a full story if they feel that the area is large enough and configured for occupancy, regardless of the roof design. Some will say that it can only be a half story if it is uninhabitable space, otherwise it is always a full story.
As an example, in my opinion a cape cod style home is a one and a half story occupancy, where some will call these two stories based on the second floor being occupied. Your size up isn't about code compliance, or your assumption on what space is or is not habitable. Your size up is meant to help responding units to get on the same page and begin to have a common understanding of the situation and problems at hand.
Calling both of these structures three stories does not accurately depict the construction features, or, more importantly, alert incoming units to the potential hazards and operational differences that would be encountered if either were on fire.
For me, I will call any structure that has a flat roof, a full storied structure, such as a three story wood frame dwelling. If there is a pitched roof, I will call it a half story, such as a two and a half story wood frame dwelling, regardless of occupancy.
I know that may be too general for some people, but for me, it works. Having a "half story" - tells the truck company - and all other fire units responding, of the presence of a pitched roof and the potential complications associated with it. As far as occupied or not, I always assume that all space is occupied, until fire service personnel determine otherwise.
Fire travel and growth is different in a half story versus a full story, particularly in balloon frame construction. Incoming units need to understand this and adjust accordingly, not only
their tactics, but their expectations on how long it will take to perform given tasks.
If your department places a priority on well coordinated ventilation, particularly vertical ventilation, then being aware of the presence of a peaked roof is vital.
Typically, flat roofs are faster and easier to perform top side ventilation on compared to a peaked roof. Flat roofs can be accessed from essentially any location, and members can walk to the area to perform ventilation relatively easily.
Peaked roof operations often have difficulties not found on flat roofs. Having steep pitches that aren't walkable, the presence of dormers, limited access for ladders, as well as the potential of having to operate from an aerial or roof ladder, could increase the possibility of making ventilation on a peaked roof more difficult and time consuming. As far as stretching a line, often it is much easier to access a third floor apartment from the front in a three story dwelling.
In a two and a half story dwelling, sometimes it is necessary to either stretch to the rear yard and go up the back stair, or stretch up the front to the second floor apartment, and then stretch through that apartment in order to gain access to the internal stair going to the top floor. Having a longer or non-traditional stretch runs the risk of complications and delays when stretching to the top of the two and a half story occupancy.
Half stories will have knee walls and void spaces not normally encountered in a full story. These areas can trap and conceal fire and allow it to grow, making conditions on the top floor difficult for both fire service personnel and occupants.
Calling both of these structures three stories does not accurately depict the construction features, or, more importantly, alert incoming units to the potential hazards and operational differences that would be encountered if either were on fire.
The full story has a flat roof, with a large void area above the top floor and below the roof. This is called a "cockloft". Since the flat roof actually has a slight pitch to allow water to run off, this void area can be quite large and will allow the fire, heat and smoke to travel up above the top floor occupancy and fill that void area. This can give occupants more time to get out, or allow fire personnel easier access and more operating time on the top floor.
Half stories typically will also have fewer windows (horizontal openings), while a full story will have many, and usually larger, windows. The limited number of horizontal openings can reduce effective ventilation efforts, as well as limit the number of windows available for VES.
Typically, a full story multiple occupancy will have more than one means of egress (stairs), while a half story will only have one means of egress.
Having one set of stairs limits the occupant's ability to escape and compounds issues when hose lines and other fire personnel are trying to access an area from the same stairs. Clogging
of the stairs, and a need for rapid egress, can quickly become an issue if fire crews aren't disciplined.
Overall, what does any of this mean to the units that will be operating or to the occupants? By the way it's constructed, the 'half story' compresses our time frame for how long we can expect to operate on that upper floor when compared to a full story.
Once fire gets into the void spaces, it can quickly travel to other areas on that upper floor, and has the potential have conditions suddenly change from clear to heavy smoke and fire once the trapped fire and smoke breaks out.
Combine this with the fact that vertical ventilation can potentially be delayed and the fact that there are fewer horizontal openings available, and this equates to interior units operating under more difficult conditions for a longer period without the relief of adequate ventilation.
More importantly, it means that occupants will have a shorter period of time where they will be able to perform self-rescue, and they will be exposed to the heat and products of combustion much faster.
By stating in the initial size-up the presence of a half story, hopefully this will give responding units a greater awareness of the potential hazards they will face upon arrival so that they can work efficiently and effectively to achieve a positive outcome.
As can be seen in the above picture, fire on the second floor quickly travels up the wall bays and into the roof bays and void spaces (particularly knee walls) of the floor above. Once these areas become involved in fire, the fire will quickly extend into the apartment.
In balloon frame construction, fire quickly travels up through the stud bays of the walls. Once the fire reaches the top of the bay, the fire will push out into the knee walls as seen in the above photos. The knee wall was opened up during attack and overhaul to completeextinguishment.
You can also see how the fire burned the underside of the roof components. If this structure had a flat roof, the fire and products of combustion would travel up and into the void space of the cockloft under the roof.
Here we can compare, side by side the differences in the number of horizontal openings in the top floors of these two buildings. The 2.5 has two windows on each the A and D sides, while the larger 3 wood has 10 windows on the front and 7 on each floor of the B side. Having fewer horizontal openings on the 2.5 wood can lead to limitations for access and egress, as well as horizontal ventilation.
Here we can see a fire that traveled up through a single bay and made it to the void at the top of the
bay in a 2.5 story balloon framed structure. This is a good example of how a relatively small fire below can quickly take hold of an entire knee wall void and cause a much larger fire above. This type of fire travel is often seen in cape cod style homes that have knee walls that can run the full length of the upper floor.
Above you can see a large void in the center of the occupancy that goes from the basement to the roof that contains the chimney. In many occupancies, it is not uncommon to find hot and cold water pipes, drain and soil pipes, electric, gas and heating components in these voids. This is another avenue that can greatly contribute to the vertical spread of fire.
A typical Cape Cod. The dormers on the second floor
are a great indicator of where bedrooms are. There will be knee walls found under the roof area on the A and C Sides that are often used as storage or to hide utilities. These void spaces, as well as voids created by the construction of the dormers and interior stairs will contribute to fire travel and the trapping of smoke and fire. If not opened up in a timely manner with the protection of a hand line, the fire can quickly grow unchecked and force units to retreat.