Is HardiePlank Siding Really Non-Combustible?

Hardie plank siding, produced by James Hardie, has gained significant popularity among homeowners due to its durability, aesthetic appeal, and low maintenance. But when it comes to fire safety, a common question arises: is Hardie plank siding non-combustible?

Given the increasing concern over fire-resistant building materials, let's delve into the matter, exploring the fire safety aspects of Hardie plank siding and debunking any misconceptions.

The Nature of Hardie Plank Siding

Hardie plank siding is composed of fiber cement, a material made from a blend of cement, sand, and cellulose fibers. This composition sets it apart from traditional wood or vinyl siding, which are combustible materials.

However, it's essential to note that "non-combustible" is a technical term defined by building codes. It refers to materials that either cannot burn or will not contribute to a fire under specific conditions.

The Role of ASTM International Standards

ASTM International, formerly known as the American Society for Testing and Materials, sets standards for a wide range of materials. When it comes to building materials, ASTM has defined combustible and non-combustible materials. According to ASTM E136, a non-combustible material is one that, when tested, loses not more than 50% of its original weight when exposed to temperatures up to 1,200°F (649°C).

Hardie plank siding, unfortunately, does not meet this stringent standard. When exposed to high temperatures, it can degrade, char, and even emit smoke. Thus, it cannot be classified as non-combustible under ASTM E136.

Fire Ratings and Hardie Plank Siding

While Hardie plank siding is not non-combustible, it's crucial to understand that it's not entirely helpless in the face of fire either. James Hardie has conducted extensive testing to determine Hardie plank siding's performance in various fire scenarios. The results are promising, with Hardie plank siding exhibiting limited flamespread and low smoke development.

Moreover, Hardie plank siding has received a Class I rating from Underwriters Laboratories (UL). This rating indicates that the product does not exhibit flame propagation under specified fire exposure conditions. This doesn't mean it's "fireproof," but it does show that it performs well in a fire, indicating reduced fire risk compared to other siding materials.

Languages of Building Codes and Hardie Plank Siding

Building codes often distinguish between "combustible" and "non-combustible" materials, with the latter typically enjoying more favorable treatment in design and construction. However, their distinctions may vary, leading to confusion about Hardie plank siding's classification.

For instance, the International Building Code (IBC) classifies Hardie plank siding as "limited combustible" based on its flame spread index. This classification acknowledges that, while Hardie plank siding can burn, it does so in a way that limits flamespread andSmokedevelopment compared to other combustible siding materials.

Hardie Plank Siding and Fire Resistance Ratings

Fire resistance ratings measure a building material's ability to contain a fire within a compartment for a certain time. Many building codes require fire-resistant siding in certain regions and on specific buildings. However, it's important to note that Hardie plank siding's Class I rating from UL does not provide a fire resistance rating.

Thus, if fire resistance ratings are required for a project, Hardie plank siding may not be the best fit. Other cladding materials, like masonry or metal, should be considered, as they often provide fire resistance ratings.

Installing Hardie Plank Siding and Fire Safety

While Hardie plank siding may not offer the same fire resistance as non-combustible materials, its installation can still contribute to enhanced fire safety. Hardie plank siding's overlapping design, when installed correctly, can create a barrier against the elements, potentially delaying a fire's spread across the building's exterior.

Furthermore, combining Hardie plank siding with other fire-resistant components, such as fire-resistant foams, membranes, or barriers, can also improve the overall fire safety of a structure.

In the grand scheme of fire safety, Hardie plank siding may not be the first choice for its non-combustibility. However, understanding its fire performance characteristics, ratings, and how it aligns with building codes can help property owners make informed decisions about its suitability for their projects. Always consult with local building codes and relevant authorities to ensure compliance with their specific requirements.