By James Johnson
Tilt-up or Tilt-wall construction is quickly becoming one of the fastest growing building methods in North America wherever large square footage is required. According to the Tilt-up Concrete Association, 15 percent of all industrial buildings in the United States were created using tilt-up construction, and the industry is growing at an annual rate of almost 20 percent.1 This construction method originated in the early 1900s by architect-contractor Robert Aiken but didn’t really gain popularity until the post-World War II construction boom.
In the past, these buildings were mainly found in commercial and industrial areas; however, they are now frequently being developed within urban centers in the form of educational institutions, low-rise apartments, and even single-family dwellings. This shift is largely a result of the economic advantage of tilt-up construction and the speed in which projects are completed when compared to traditional steel-frame or masonry buildings.
The construction process of the exterior walls begins by pouring large slabs of concrete horizontally on the construction site. Once cured, these panels (usually six to 12 inches thick and weighing 40 to 70 tons) are “tilted” up into place to create the outside structural walls. Once they are placed in their permanent position, the walls are temporarily braced until all the subsequent walls are erected and the roof system is installed (photo 1). The roof system typically consists of a series of large steel beams and lightweight open-web steel roof joists welded to steel plates. These steel plates are imbedded in the walls during the forming process. Once the roof system is in place, the whole building now acts as a cohesive structural unit, and the braces are removed.
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The design of tilt-up buildings is based on the concept that the roof system and walls work in cohesion to create a structural diaphragm; however, there are potential dangers in the case of a fire. Should one component fail in this type of construction, causing other components to carry the excess load, there is the potential for total failure. That is why it is crucial for firefighters to be able to recognize these buildings and prevent damage to the structural components in the case of a fire.
When arriving on scene to an alarm in a suspected tilt-up building there are a few characteristics that can help us to recognize these buildings:
The Exterior
During our initial size-up, the physical appearance of the exterior walls can speak volumes. In tilt-up construction, the walls are typically smoother in appearance when compared to steel (photo 2) and masonry (photo 3) construction. They may also have an architectural design embedded in the panels in the form of reveals placed in the formwork prior to placing the concrete (photo 4). Many buildings are either painted or covered with an acrylic coating. In some cases, you might find that the rear of the building, which typically is not as publicly visible, might not have been finished (to lower cost) and ma give you a clear view of the panel.
In commercial and industrial applications, typically one- or two-story tilt-up buildings have larger individual panels that each measures 30 feet by 30 feet in dimension. This size allows the panels to be a reasonable weight; they can be lifted by a portable truck-mounted crane. With the wall dimensions characteristically 30 feet or less in width, panels are connected in two main ways to create long spans–butt-jointed (photo 5) or overlapped (photo 6). An overlapped appearance is a classic architectural characteristic of tilt-up construction. Both of these methods allow a small gap (one-half to three-quarter inch) to provide room for insulation and caulking.
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The Interior
Ideally, we should know the construction type before we enter a structure; however, once inside the building, there are a few features we can look for to confirm our initial size-up. In photo 7, you can see the interior wall of a completed and operational big box store. Many times in these types of occupancies, the panels remain unfinished and certain building components–such as the connection points for lifting and bracing, connection weld plates, and the caulked joints–are visibly exposed. They all are distinct telltale signs of tilt-up construction.
In recent years, there have been big changes to building codes for tilt-up buildings in regard to energy efficiency,2 and many North American regions are now obligated to meet specific insulation requirements. Here in Western Canada, these requirements are usually met in one of two ways. The first, and most common, method is achieved by creating insulated panels. These panels typically have two to three inches of ridged insulation sandwiched between two layers of reinforced concrete to create one solid panel (photo 8). The second method is to build another wall on the interior directly in front of the tilt-up panel. The standard thickness for this wall is six inches, and the wall is constructed using steel studs. This wall is then filled with fiberglass insulation covered with drywall; in commercial settings, the wall is often completed with a layer of plywood.
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This second method of insulation can be problematic for firefighters for a few reasons. This insulation wall, although small, leaves a void space that creates the potential for fire spread behind the drywall. Second, having the whole interior of the panel covered by a secondary wall makes it nearly impossible to recognize key features and also takes away our ability to see any signs of impending collapse in the wall itself. Last, when used in a commercial or an industrial setting, a layer of plywood is used to cover and protect the drywall, which creates a combustible surface and increases the fire load.
Firefighters and fire officers need to fully understand these buildings and the dangers associated with them. If we can ensure that our members are entering these buildings with a thorough knowledge of their method of construction how building components will react when subjected to fire, then we can be more confident we will make the safest tactical decisions.
Endnotes
1. Tilt-Up Concrete Association: Mt Vernon, Iowa: www.tilt-up.org.
2. American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) ASHRAE 90.1-2007: www.ashrae.
BIO
James Johnson is a firefighter with Vancouver (BC, Canada) Fire and Rescue Services and has been involved with the fire service since 2003. He is passionate about building construction and instructs on that topic. He is a certified Red Seal Journeyman Carpenter, a fire service instructor, and an FDIC International presenter.
