Building Size-Up

Laying a solid foundation

Throughout the North American fire service, there are a wide range of approaches taken by firefighters in the manner in which they size up the physical structure during a fire and the amount of information that is passed along to incoming units. Some use the traditional five types of construction (fire-resistive, noncombustible, ordinary, heavy timber, and wood frame), while others give a physical description of the building. Some will describe the building based on perceived occupancy such as commercial or residential and, unfortunately, many do not include any information at all. The size and age of the structure, types of materials used in the construction, and use or occupancy of the space are arguably some of the most important factors that affect our strategies and tactics during a fire, and neglecting to identify hazards associated with the building can have devastating consequences.

Age: New/Modern. (Photos by author.)

Age: New/Modern. (Photos by author.)

Missing Information

In an ongoing study titled “Project Mayday,” Don Abbott has undertaken a comprehensive investigation into 2,868 Maydays that have occurred over a 30-month period. Of the hundreds of statistics and factors that have been identified throughout the study, one that immediately jumped out at me was that in 54 percent of the recorded Maydays in the project, building construction was never identified during the initial size-up. Although the construction may not have necessarily been a contributing factor in the initial cause of the Mayday, it certainly showcases the fact that we are still missing this critical piece of information on a regular basis.

I am a very firm believer that a size-up of the building is something that should be done by every single member on the fireground and continuously monitored as the incident evolves. There are numerous examples of fires that have resulted in building collapse and, fortunately, the firefighters on scene were able to recognize and identify preliminary signs of collapse prior to the collapse itself. Several of these fires would have certainly resulted in line-of-duty deaths if the signs of building collapse had not been identified and communicated. This is one of the reasons that I personally dislike the practice of donning the self-contained breathing apparatus face piece in the rig prior to arrival, as I feel that it severely restricts the individual’s ability to complete a size-up of the structure. The initial size-up creates an important benchmark that allows us to see if conditions are either improving or deteriorating.

 Size: Medium 21⁄2-story with basement.

Size: Medium 21⁄2-story with basement.

My personal approach to building size-up (and most things within the fire service) is that simplicity reigns supreme. I believe there are many benefits in having a simple standardized size-up methodology, one that also allows for additional information to be added, based on the level of experience or building construction knowledge of the individual. When I am approaching a building that is on fire, either as the apparatus operator or riding backward as a firefighter, I am initially trying to determine two things from a structural perspective: how the fire will spread and how the building will fail. I do this by attempting to identify the size, age, materials, and use of the building. This is similar to the methodology that Dave Dodson and John Mittendorf describe in The Art of Reading Buildings. I believe that when these four characteristics are combined with a prior knowledge of building construction and an understanding of the types of structures commonly found within your city, they provide a solid foundation for an initial size-up.

Materials: Noncombustible concrete tilt-up construction.

Materials: Noncombustible concrete tilt-up construction.


The size of the structure is the first thing that most firefighters automatically recognize when arriving on scene. Whether it’s a small two-story house or a large one-story warehouse, these physical attributes are generally easily identified and communicated to incoming units. Some agencies have their officers give a rough estimate of the size of the structure, such as 20 feet by 60 feet.

I do like this approach in theory; however, there tend to be two major drawbacks to estimating the size in this manner: The approximate size rarely ends up being accurate, and the majority of the time you still have to arrive on scene to orient yourself as to which direction is which. The simple description that I like to use for the size of a building is small, medium, or large. I realize some may feel that this is an oversimplification but, when combined with the age and use of the building, I believe it paints an adequate picture that most firefighters can relate to. Another thing to take notice of is the shape of the building, as it can often give you clues to the direction that structural members such as joists, rafters, and trusses may run.


Identifying the age of the structure is one of the more challenging aspects of the building size-up. Frequent remodels and updates to older structures only add to the level of difficulty of truly knowing the age of the building and the type of structural members contained inside. Another issue with attempting to identify the age is, quite frankly, a lack of building construction knowledge. If someone doesn’t understand the significance of a pre-1933 masonry building, or the likelihood that a wood-frame home built before World War II will be balloon frame, then their personal size-up is destined to fail.

Virtually every type of building has significant differences in the materials and methods used based on the period in history in which it was built. It is important to first understand these differences and how they correlate to the buildings found in the city you serve. A great resource for learning the age of buildings common to your area is visiting real estate Web sites. These online listings contain photographs of the exterior of the building along with a written description and the year that it was built. By doing this, we start to see common trends in the design aesthetic of buildings of a similar era.


The materials and structural assemblies that we will find in a building are often dictated by the other three characteristics: size, age, and use. For example, a large, newly constructed, single-family residence with an open concept floor plan will most likely require engineered building components in the floor or roof system to achieve the spans the structural members will require for the design. Conversely, a small one-story home built at the turn of the century will be much more compartmentalized and contain dimensional framing lumber throughout. When looking at a building, I try to identify if the materials are primarily combustible or noncombustible, as this will indicate if they will contribute to the fire load. Then, based on the age, I try to determine if the building has engineered components, as this can affect the size of the void spaces and how the fire will spread throughout the structure.


The use of the building is the final piece of the puzzle and is an aspect of the size-up that is often started once the initial dispatch is received. The use of the building is commonly differentiated by either residential or commercial and, when combined with the size of the building, can also be an indication of the materials involved. For example, a large building with a high occupant load such as a school or a hospital will most likely be constructed of protected noncombustible structural components.

Like most aspects of the fire service in which a variety of techniques can be used to complete the same task, there are many ways to accurately size-up the building. Whether you choose to implement the four characteristics of size, age, materials, and use within your size-up protocol, the most important part is ensuring that you have a system in place prior to the alarm sounding that is rehearsed, simple, and easy to remember and ultimately contributes to our mission of safely and effectively protecting lives and property.

By James Johnson

James Johnson is a firefighter for Vancouver Fire and Rescue Services in Vancouver, British Columbia, Canada. He is assigned to Firehouse 1 and is part of the special operations technical rescue team as well as Canada Task Force One USAR Team. Johnson is a certified fire service instructor II and teaches at the Justice Institute of British Columbia in the fire and safety division. Before becoming a career firefighter, he spent a number of years in the construction industry and completed an apprenticeship and the technical training to become a Red Seal journeyman carpenter. Johnson serves as a technical committee member for NFPA 5000 and is an FDIC presenter.

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