What Is Fire-Resistant Construction?

Our Boulder community has just come out of a heavy month, amongst a heavy year, of suffering great loss and devastation due to wildfires. If your home and livelihood have been affected by the wildfires, we express our deepest condolences. Our hearts are with you in your grieving. 

As we begin to heal and look toward the future, our Tectonic Design + Build team would like to extend a helping hand. If your home has been damaged, we’re here to guide you through the rebuilding process. 

Along with that, we’re committed to providing our entire community with more information on how durable, fire-resistant building techniques and materials can help protect us from further loss. In this article, we’ll start with the basics of fire-resistant construction, as well as which building materials can be used to achieve it. 

What Is Fire-Resistant Construction?

Fire-resistant construction is a method of construction that involves the use of flame-resistant materials that can slow down or prevent fires within a structure. It takes into account the ignitability of the home itself and the defensible space around it — two components that combine to create the concept of a Home Ignition Zone (HIZ). 

In wildfire prone areas, the goal of fire-resistant construction is to reduce or eliminate as many ignition sources within the HIZ as possible. While it’s not feasible for an HIZ to be completely fireproof, there are many building techniques and materials that can dramatically slow fires down, allowing more time for people to escape and for first responders to get to the scene. 

What Are Fire-Resistant Building Materials?

Now we’ll dive into a key component of the fire-resistant construction process: choosing fire-resistant building materials. As mentioned above, these materials are designed to resist ignition for longer periods of time, slowing down the spread of a fire — not fully preventing it.  

Fire-resistant building materials generally have ratings, most of which were established by the American Society for Testing and Materials (ASTM). These fire ratings are based on ASTM’s flame spread index (FSI), which measures how quickly a material can burn and spread flames. 

From there, building materials are separated into 3 classes based on their FSI measurement, which are:

  • Class A: FSI 0-25
  • Class B: FSI 26-75
  • Class C: FSI 76-200

The lower the rating, the more fire-resistant the building material. Therefore, for fire-resistant construction, you’ll want to make sure all of your materials are labeled Class A.

5 Categories of Fire-Resistant Building Materials to Consider

Not sure where to start your fire-resistant building material search? No worries! Here are the five main categories of building materials and their corresponding fire-resistant options.

Fire-Resistant Foundations

A resilient, fire-resistant home starts with a durable, fire-resistant foundation — and for that, insulated concrete forms (ICFs) should be your top choice. ICFs are polystyrene blocks that connect together to create your home’s shell. Their concrete composition makes them one of the most fire-resistant building materials available.  

ICFs have an estimated burn time of 4 hours, meaning that it would take four hours of continuous fire on the outside for the flames to reach the inside of the home. Most wildfires tend to blaze past homes and burn out much quicker than that, ensuring your home is well-protected. And when you compare that long burn time to the estimated 15 minutes of traditional, wood-framed foundations, you can see how ICFs can make a world of a difference when it comes to building a more resilient home. 

Fire-Resistant Siding/Exterior Walls

There are a number of fire-resistant siding and exterior wall materials to choose from, but the most important thing to remember is to avoid plastic. Materials like brick, stucco, cement, and gypsum will prove much more resistant to flames. 

At Tectonic, we recommend cement-based siding products, like those from JamesHardie™, for the best results. Their fiber-cement siding products are extremely durable, offering high-performance and protection in various climatic conditions, including wildfires. 

Fire-Resistant Roofing

While having a fire-resistant exterior structure is important in preventing damage, you’ll need to pair it with a fire-resistant roof as well. It’s best to avoid wood shingles of any type, regardless of their treatment or rating, and to look for materials labeled Class A. You’ll have the best luck looking at materials like tile, slate, standing seam metal, or cementitious composite shingles. 

The material you use for your roof definitely matters — but it also depends on how it’s used. In many cases, roofs that have steeper slopes perform better in case of a fire. This is because embers can roll off your roof before they have a chance to burn through. 

Fire-Resistant Windows

Windows are a necessary component to any healthy home, but they also usually bring the most risk in the case of a fire. A fire’s extreme heat can easily shatter glass before its flames can even enter. That’s why it’s important to install insulated, double-glazed windows with tempered glass on the exterior. 

For extra protection, you may also consider installing fire shutters on the exterior of your home, which are generally made of galvanized or stainless steel. These flame-resistant shutters have an estimated burn time of 1-4 hours. 

Fire-Resistant Decking

Any outdoor living space you have is likely in your home’s defensible space, so it’s critical that you use fire-safe materials to build that too. For decking specifically, make sure to avoid wood and opt for composite or concrete materials instead. 

For best results, ensure that the underside of your deck is not exposed. This building technique can prevent embers from reaching underneath. 

Other Considerations for Building a Fire-Safe Home

Aside from those five main categories of fire-resistant building materials, there are some other techniques to keep in mind during the construction process. While you may not have put much thought into these things before, they could make all the difference in the case of a future emergency. 

    • Clean your gutters out annually. Any debris that builds up can fuel the flames of a fire that reaches your home. 
    • Cover your chimney with a nonflammable screen. This can prevent embers from either entering your home or from escaping your home and starting other fires. 
    • Cover your vents, soffits, etc. with a metal mesh no larger than ⅛” in size. This can also prevent embers from entering your home.
    • Ensure your driveway is always accessible and your address is always visible. Keep trees and shrubs at least 30 feet away from each side of your driveway, and post noncombustible, easily visible signs with your house numbers at the end of your driveway. This will help first responders find you quickly. 

In a world of ever-changing environmental conditions, fire-resistant construction is always an initial consideration in our design-build process at Tectonic. We’re committed to building healthy, high-performance, resilient homes with safer materials, so that our Boulder community can be protected from further devastation. If you’re looking to rebuild for the future, contact our team. We’re happy to help get you started. 

Looking for more resources on fire-resistant construction and building materials? Check these out: 



Matching your goals with a remodeling contractor in your area doesn’t have to be difficult. If you’re looking for a larger-scope remodel that prioritizes performance and craftsmanship, the Tectonic Design + Build team is the Boulder, CO remodeling contractor for you. Reach out to learn more about what we do and how we can help facilitate your upcoming project.