Exploring the Main Types of Building Construction

The International Building Code (IBC) is a model building code, and it was developed by the International Code Council. The IBC’s goal is to create uniform building practices for the sake of public health and safety. It also plays an important role in defining the different construction types.

The IBC defines the different types of construction for several reasons. First, it determines the structural design criteria for a project to ensure that it is strong and safe enough for the intended occupancy. It also ensures that all of the components and utilities in the structure are up to code to ensure the building can last in the event of a fire.

There are five main building construction types. They include Type I Fire-Resistive, Type II Non-Combustible, Type III Ordinary, Type IV Heavy Timber, and Type V Wood Frame. Each type meets different specifications established by the International Building Code (IBC) concerning materials used, design, and fire rating.

• Type I: Buildings over 75 feet tall and made from concrete and steel
• Type II: Buildings made from reinforced masonry or tilt-slab walls and metal roofs
• Type III: Buildings with non-combustible walls but wood-framed roofs
• Type IV: Buildings made from heavy timber
• Type V: Modern buildings with standard wood-framed walls and roofs

Type I: Fire-Resistive

Type I buildings are “Fire-Resistive,” which means they’re designed to withstand high temperatures for long periods without catastrophic collapse. Type 1 buildings, by definition, are over 75 feet tall and made from reinforced concrete and protected steel. Other materials within the building are coated with fire-resistant treatments to further increase their fire resistance.

There are additional important characteristics of Type 1 buildings, as well. For one, all of the building materials are non-combustible. Also, these buildings are designed to withstand extreme temperatures for up to 4 hours and to prevent collapse. Many have specialized HVAC systems and pressurized stairwells that help the building self-contain fires.

Type II: Non-Combustible

Non-combustible buildings are known as Type II construction. These buildings are constructed with materials that will not act as fuel for a fire. They’re generally built from reinforced masonry or tilt-slab walls and non-combustible roofing materials like metal and concrete. Some examples of Type II buildings include schools, hospitals, industrial factories, retail buildings, and shopping malls.

Type II buildings are designed to withstand fire for one to two hours, depending on the materials. Components like columns, beams, flooring, and decks are designed not to burn within that time frame. These buildings are also designed to contain fire and smoke in compartments within the building. Thanks to the fire door and fire-resistant partitions that separate them, it allows fire suppression systems to knock fires down before they can spread.

Type III: Ordinary

An ordinary building, or Type III construction, features non-combustible exterior walls with combustible roofing structures. These buildings may feature non-combustible tilt-slab or reinforced masonry for the exterior walls. However, the floors and roofs can be standard wood-framed. They also feature fire-cut joists, which can separate from the wall in a fire, preventing collapse.

Ordinary construction is common in commercial buildings, residential structures, and low-rise buildings. While these techniques have been around for many years, modern buildings can still be constructed with Type III methodology. The balance between fire resistance and affordability makes it a popular construction method.

Type IV: Heavy Timber

Type 4 buildings are also known as heavy timber buildings due to the thick structural wood members that support them. The exterior walls of these structures are non-combustible, but the interior columns, beams, and girders are made from thick wood boards. These beams are connected to the structure of the building with metal braces, brackets, and hardware.

Common heavy-timber structures include churches, historical buildings, and recreational facilities, most of which would be built before 1960. The IBC requires that beams in these structures be at least 8 inches thick, as thickness makes them surprisingly fire-resistant despite being made from wood. Since the load-bearing exterior walls are non-combustible and the beams are fire-resistant, these structures often fare well in fires and aren’t as susceptible to collapse as one might think.

Type V: Wood-Framed

Type V buildings are the only structures on the list to allow combustible exterior walls. These structures are built from standard dimensional lumber in both the exterior walls, floors, interior partitions, roofing structures, and more. Dimensional lumber is affordable and readily available, but these are the buildings most susceptible to fire damage. Common Type V structures consist of houses, residential buildings, townhouses, and some low-rise apartment buildings.

While wood-framed structures have their drawbacks, there are also some benefits. For example, these structures feature horizontal platforms that can help prevent the vertical spread of fire. Also, the dimensional lumber is covered with drywall, which can resist fire for anywhere from 30 minutes to an hour (two hours is possible, as well).

To the average person, a building’s construction type is not a top-of-mind concern. However, there are some good reasons why these types exist and are classified the way they are. When firefighters arrive on the scene of a fire, they have different tactics they have to use to save lives and property.

• In Type I buildings, firefighters focus on securing evacuation points like stairwells and exits, as these structures are generally safe and can prevent inhabitants from getting trapped.
• In Type II buildings, firefighters have to prioritize ventilation, which could mean anything from opening doors or cutting holes in the roofs. This approach prevents a dangerous heat build-up known as “flashover.”
• For Type III buildings, firefighters can vent the building, but since many of these structures have crawl spaces or attics, the fire can spread quickly.
• Type IV buildings are tough and resist fire well, but fires in these structures require a lot of water to put out all the burnable material.
• Type V buildings can ignite and become completely engulfed faster than other building types. Firefighters know how to approach these homes quickly and carefully. They may vent roofs by cutting holes, but flashover is always a concern.

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