Before a building is constructed, it’s important to determine how it will perform in the event of a fire to ensure occupant safety and property preservation. Builders do this by classifying the building based on its fire resistance. Some buildings are classified as fire resistant or constructed with materials that can withstand fire for longer periods to prevent fire from spreading. Others, on the other hand, are classified as non-combustible or built with materials that provide less fire resistance than those of Type I. Here, we will look at non-combustible construction, also known as Type 2. Type 2 is one of five types we’ll explore in future articles.
Local building codes regulate the fire resistance of buildings, determining what type will be used in a given structure. This affects the GC and subcontractors who must adhere to these standards. It’s helpful for subs to obtain a general working knowledge of the five types of construction, how they apply to commercial buildings, and why they sometimes inhibit the use of certain building materials. We will explore the advantages, challenges, and standard materials of Type 2 construction.
Table of Contents
What Is Type 2 Construction?
Type 2 construction, also known as non-combustible, is a building classification in which the walls, columns, partitions, floors, and roofs are made of non-combustible materials. This type of construction uses the same types of materials as type 1 or fire-resistive construction, but the structural components do not have fire-resistant coatings and insulation, making them susceptible to collapse. If fire protection is provided, it is of a lower rating than that required for Type I construction.
The term “non-combustible” refers to the fuel the building contributes in case of a fire and does not indicate its resistance to fire spread. However, the materials will provide one to two hours of burn resistance.
This type of construction is commonly used in newer school buildings and warehouses. These structures typically have unprotected metal floors and roofs that can collapse prematurely when exposed to fire.
Failure to cool the ceiling area will allow heat to weaken unprotected steel, potentially leading to collapse or contributing to a fire on the metal roof deck. As a result, the primary goal of firefighters is to ventilate the entire structure by using skylights or roll-up doors on the building’s exterior. This ventilation will help prevent flashovers or sudden dangerous temperature spikes, particularly in warehouses that store a variety of commodities that can contribute to fires.
When Is a Building Classified As Type 2?
A building is classified as Type 2 based on its fire-resistance rating. We use the standard fire resistance test to determine how long an element can withstand flames, heat, and extreme temperatures.
The fire resistance test measures the building’s resistance to collapse, resistance to temperature rise, and resistance to flame penetration or passage on the unexposed side.
Most countries define fire resistance in terms of time, such as 0 hours, 1 hour, or 2 hours. A 0 fire rating indicates that the materials will typically collapse in less than an hour.
Type 2 structures have a one to two-hour rating depending on the building components.
Determining Authorities for Construction Classifications
There are two major sources for identifying construction types: the International Building Code (IBC) and the Insurance Services Office (ISO).
The IBC requires that the building elements have a fire-resistant rating not less than that specified in Table 601, while the ISO provides data, risk management, underwriting, and legal services to insurers and clients.
ISO has its categories of construction types, namely:
- ISO 1. Known as “Frame,” it is the class for combustible walls and roofs.
- ISO 2. This is known as “Joisted Masonry” or JM. It’s for non-combustible masonry walls with a wood frame roof.
- ISO 3. This is the “Non-combustible” category or NC. It has very minimal combustible materials involved in construction.
- ISO 4. This refers to the “Masonry Non-combustible Category” or MNC
- ISO 5. This is the “Modified or Semi Fire Resistive,” known as MFR or SFR.
- ISO 6. This is the “Fire Resistive” category.
Because type 2 construction is non-combustible, we can categorize ISO 3 or 4 construction as type 2. On the other hand, IBC is more descriptive than ISO as it includes A and B types of construction.
Types of Type 2 Construction
Type 2 construction, like type 1 construction, is divided into two types: 2A and 2B. These types are non-combustible but have little to no fire resistance.
Type 2A, or “Protected Non-Combustible,” requires the application of fire-resistant materials to the building elements. All structure elements have a minimum of one-hour fire protection, lower than that of type 1 construction.
This type is used for smaller buildings that cost less, and the intent is to preserve life so there are fewer occupants.
Type 2B, or “Unprotected Non-Combustible,” has no fire resistance requirements, exposing structure elements.
What Materials Are Type 2 Buildings Constructed With?
Type 2 buildings are typically made of steel, metal, or concrete blocks. Its structural framework may be similar to type 1 construction. However, its roofing may contain combustible materials.
Metal framing members, reinforced masonry or tilt-slab walls, metal cladding, and metal deck roofs with unprotected open-web joists are common in this type of construction.
Sometimes lightweight concrete is used for roofing. However, asphalt waterproofing and a combustible felt paper covering might also be present. Regardless, the other materials used can be almost as fire-resistant as those used in type 1 construction.
What Are the Drawbacks of Type 2 Construction?
While these buildings are composed of non-combustible elements, they are not safe against flashovers. Because of their metal roofs, Type 2 buildings are prone to early collapse due to high temperatures, even if they are not directly affected by the flames.
Suppose the ceiling area is not cooled quickly. In that case, it will allow heat to weaken unprotected steel members, making them susceptible to expansion, distortion, or relaxation, resulting in an early collapse during a fire.
Type 2 buildings also typically have flat roofs that often contain combustible materials such as felt, insulation, and roofing tar. If a fire extends to the roof, it can cause the entire thing to collapse and fail. Sufficient ventilation is necessary to avoid heat buildup from fires
Furthermore, because non-combustible doesn’t necessarily mean fire-resistant, structures may only have materials with no fire ratings in limited quantities. For example, you won’t be able to use untreated wood for the major parts of the building.
Challenges in Type 2 Construction
Because of how it’s built, a building of type 2 construction may mean:
- It’s difficult to breach for access during emergencies
- It’s challenging to secure the needed ventilation during a fire
- Debris would fall during the collapse
- Floors, walls, and ceilings retain heat
- Steel components can be weakened by fire, rust, and corrosion
Regardless, it is still second to the most fire-resistant construction type. These structures can provide some safety during a fire as long as proper systems are in place.
What are Type 2 Construction Examples?
Type 2A construction is commonly used in newer school buildings, while Type 2B is in commercial buildings.
Examples of Type 2A structures include:
- Daycare facilities
- Educational institutions up to 12th grade
- College institutions
- Religious, educational buildings
Examples of Type 2B structure include:
- Large box-type department stores
- Shopping malls or strip malls
- Retail or wholesale stores
Generally, Type 2 construction is most common in remodeled commercial establishments. They usually feature exposed metal floors and roof systems. They also use metal and masonry walls as building elements.
Getting acquainted with the nuances of construction, like the five types of fire resistance in buildings, can help you become a more well-rounded subcontractor who can better navigate building codes and regulations.