What is fireproofing?

Fireproofing is to extend the time an item can be exposed to fire before it fails. In construction this is referred to as passive fire-protection as it does not extinguish the fire but rather prevents failure. Typically this is done by applying a fireproofing material to structural members.


While the term fireproofing may seem to imply that an item cannot burn or fail, this is not the case. In reality, no building material or system is completely fireproof. All physical structures and components have limits and can be irreparably damaged by fire. A more proper term would be fire resistant as it only protects the structure for a prescribed period of time.

 Although there are different materials and methods of doing this, all systems follow the same basic principle.  A product is used to separate the item from the fire, which will insulate and delay the transfer of heat. This can be achieved in different ways but the basic principle always stays the same. 

Regardless of the above, fireproofing a structure is an effective way of  preserving structural integrity for a period of time during a fire. This is important as it allows people a chance to escape and gives firefighters the ability to safely enter the structure and provide fire rescue services.

When is fireproofing required?

Fireproofing is required in order to ensure a structure or a part of a structure will not fail for a period of time during a catastrophic fire. National and regional building codes will determine what fire-rating is required for a given structure.

 The given fire rating is referred to as an hourly rating. This is typically either one, two, three, and occasionally a four hour fire-rating.  

The required rating usually depends on the construction type and use group. There are also often more than one use group in a structure. In these instances a separation between uses may be required with a fire rating higher than the rest of the structure. 

Buildings may be designed and constructed with fire resistance-rated walls, floors and ceilings and a design must be provided showing all components of a given assembly and the provided rating. When all details of a design are followed, the assembly as a whole is to be considered fire-rated. This is often referred to as a fire-rated assembly.

A thorough understanding of building code is needed in order to determine the fire ratings needed for your project. These are typically called out by the architect and can be found in the construction documents. 

Fireproofing steel

While there are different methods to fire rate a structure, steel construction is generally fire rated with a fireproofing material. This will usually be either cementitious (spray fireproofing) or intumescent fireproofing.

A common misunderstanding is that a building component needs to either combust or melt in order to fail. Therefore people wonder, when will this ever be needed on a steel structure? Isn’t steel non combustible and able to withstand temperatures in excess of 2000°F?  The simple answer is, you don’t need the structural member to completely fail in order for a disaster to occur. When designing a building, the engineer will put enough steel to handle the intended load. When steel hits extreme temperatures, it weakens and loses some of its structural capacity. All that’s needed for a failure is for the steel to reach a point where it can no longer handle the intended load.

When designing a project and specifying a product, care must be taken to choose the most appropriate material that complies with the code requirements of the structure getting rated. Aside from the required rating, there are variables in material capabilities and properties. Code may require materials with specific characteristics depending on building height and other factors. Additionally, not all materials are created equal and the environment and location play a big part in choosing the correct product. Some situations may require materials with specific approvals and properties.

What is spray fireproofing (cementitious fireproofing)?

Cementitious fireproofing is often referred to as spray applied fireproofing or SFRM for short. This coating is either gypsum or portland cement-based and is the most common form of fireproofing. 

spray fireproofing

Fireproofing contractors will use specialty machinery to mix water and material. Then using compressed air, they atomize and spray apply the fireproofing to the correct thickness for the required rating. When the cementitious material completely dries, it forms a barrier. This coating will act as an insulator and significantly delay heat transfer. In the event of a fire this will protect the building structure from failure for the prescribed time.

Not all cementitious fireproofing is created equal, so you need to choose a product that is best suited for your project as well as the environmental conditions your building will encounter. Some fireproofing is more durable, and some are better suited for high-moisture areas. Some products are designed for conditioned spaces while others are tested for durability in freeze-thaw cycles.

In addition to the above, cementitious fireproofing comes in different densities which are broken down into three categories, low, medium and high density. Higher density materials will have different properties then lower density materials. Higher density materials may be required by code depending on different factors. 

More on cementitious fireproofing.

What is Intumescent Fireproofing?

Intumescent fireproofing (IFRM) is a fire resistant coating that is designed to protect structural elements during a fire. When exposed to extreme heat, the material will expand 25 times its original thickness and char, creating a layer that can protect your structure for a period of time. 

Intumescent fireproofing

While significantly more expensive than spray fireproofing, intumescent can provide a beautiful finish and allow you to keep structural components exposed and incorporate them into your design. It might also be necessary to use intumescent fireproofing where there are environment considerations (e.g., heavy industry settings) or space restraints.

Care must be taken when selecting Intumescent as not all products are created equal and depending on the situation some are better suited than others.

More on Intumescent fireproofing.

How is fireproofing thickness calculated?

A UL design is typically followed for a given assembly or structural member. The design will provide a thickness and what hourly rating it achieves. Fireproofing contractors will then use an equation such as W/D or A/P in order to add or subtract fireproofing for variable steel sizes.

Drawing showing how fireproofing is calculated

While the thickness given in the design is good for the structural member used in the test, different sizes of steel have variable thermal capacities and may require more or less material to achieve the same rating. These equations take into consideration the weight and size of the steel member and equate for the higher or lower thermal capacity.

The contractor then provides the architect with submittals and supporting documents. The submittals show what fireproofing material will be used, where and at what thickness. The architect will then review the documents to confirm that the thickness is correct for the given design and hourly rating. 

Once the fireproofing is applied, a third party inspector will typically be called to inspect. The inspector will review the approved submittals and confirm that the material was installed as designed.