Most people see buildings as simply that: buildings. But if you’re a contractor or even a firefighter, you develop a keen eye to view structural elements differently. The material choices for floors and roofs tell a story, and the architecture and construction of exterior walls speak volumes.
Contractors, especially those involved in fire restoration, know better than anyone that building construction types matter. With real-life implications regarding safety, structural integrity, and fire resistance, understanding the five types of building construction is an essential part of a contractor’s job.
Here, we’ll go over the main kinds of construction and the implications that each of these types has on your construction and restoration approach.
Type I (IA and IB) - Fire-resistive
If you have to crane your neck way up to see the top of a building, there’s a good chance it’s a Type 1 fire resistive structure. This category of construction applies to high-rise structures with a few exceptions and boasts the highest fire-resistance out of the five types of building. High-rises are typically at least 75 feet in height, so maximum fire resistance is imperative for safety.
Type 1 structures are strategically made of poured concrete and steel coated with a fire-resistant material (often a concrete mixture). This kind of construction keeps a blaze from spreading rapidly by holding it to a specific room or floor. Hindering fire spread allows help to arrive and inhabitants of the building to escape.
Emergency ventilation becomes a challenge here. The concrete construction of columns, floors, and roofs makes it nearly impossible to cut a hole in the roof of the building, and horizontal ventilation in a fire is also challenging due to the thick, tempered glass of the windows. That’s why building codes require that Type 1 fire-resistive structures have intricate fire resistance systems in place, like self-pressurizing stairwells and HVAC systems to encourage air movement.
Both 1A and 1B are incredibly fire-resistant, but a few minor differences separate them. Ultimately, Type 1A comes out on top with the best fire resistance of all five types of building construction.
Type II (IIA and IIB) - Non-combustible
Most commonly, you’ll see Type 2 non-combustible construction in newer buildings or in commercial structures that have undergone remodeling. Here, the structural elements are made of exclusively non-combustible materials. The construction is similar to that of Type 1 buildings, but the fire-resistant requirements are slightly lower.
In Type 2 non-combustible buildings, you’ll find reinforced masonry walls or tilt slabs as the structure’s exterior walls. Floors and roofs in these buildings are also non-combustible, with floors commonly covered with lightweight concrete and roofs foam-insulated with metal construction. However, these structures are not nearly as durable as Type 1 buildings when it comes to full-on fire resistance. Type 2A requires at least 1 hour of fire resistance, while Type 2B doesn’t have any specific fire resistance regulations.
Type 2 structures are newer buildings, so they are typically up-to-date with current fire suppression guidelines and codes. However, because they use steel and metals in the construction of roofing, Type 2 buildings are at risk of roof collapse during a fire, caused by the distortion, expansion, and relaxation of the steel members when exposed to extreme heat.
Type III - Ordinary
Type 3 is known as Ordinary Type. This is the most common of the types of building construction amongst older buildings, although it is still seen in newer construction. In Type 3 Ordinary construction, you’ll typically find non-combustible materials in structural members like exterior walls and roof systems made of “ordinary” materials such as wood. In addition, newer buildings are more likely to have a lightweight roof supported by reinforced masonry. In comparison, older buildings have conventionally framed roof systems and masonry walls that are not reinforced.
These structures are typically around 2-3 stories in height and rarely exceed six stories. Roof system types in Type 3 buildings include parallel chord trusses and panels. While there are some standards that you can expect in this type of building, there is also great diversity. If you look anywhere in the US, you’ll notice Type 3 structures are a standard across the country. As such, local or easily accessible materials are often utilized during construction.
Type IV - Heavy Timber
Type 4 Heavy Timber buildings are typically older structures that use large dimensional lumber as structural elements, internally and externally. Since Heavy Timber Type construction dates back to before the 1960s, many of the structures we see today using Type 4 use bolts and metal plates as connectors.
While it is commonly known that timber is combustible and burns quickly, these structures have a unique fire-resistant nature due to the large size of the timber beams used. They must measure at least 8 inches in diameter for walls. While this does slow down the force of a fire, the wooden nature of columns, floors, and roofs means there’s a greater likelihood that other damage—like that of termites and weather�� has occurred over time, and it is not unlikely that roofs will collapse during a blaze.
Type V - Wood-Framed
Unlike a non-combustible type of construction, Type 5 Wood Framed structures can use combustible materials in their exterior walls. It is common for many of the structural members in this type of construction to be wood. Typically, if the walls are wood-framed, the roof will be as well. In a fire, this type of structure can collapse incredibly quickly.
Despite the massive risk of severe damage in a fire, this is an incredibly popular construction method for modern, single-family homes.
The Bottom Line
No matter what project you are working on, it is imperative to understand and recognize the five types of building construction when you encounter them.
The different types of building construction require different standards and must meet other codes. And, in the event of a fire, they all demand various courses of action, both to limit spread and to restore the building in the aftermath.