Top 6 Fire-resistant Building Materials

Natural building materials such as lumber and cotton typically offer very poor fire resistance compared to dense concrete and plaster. The plant-based substances make for easy fuel and are quickly consumed by flames. However, builders have access to specialized chemical treatments that can increase their resistance, making them able to stand up to fire for several minutes [source: Greenfiber]. Instead of being consumed right away, flame-treated wood creates a charred barrier around its surface that slows further burning. This type of lumber is often used on exterior features that could catch sparks before reaching a home's interior [source: Forest Products Supply Co.].

Treated cellulose insulation also acts as a flame-resistant alternative to common insulators like fiberglass and cotton. The cellulose is mostly sourced from recycled paper, and is chemically treated with borate fireproofing, making it much less flammable than it would be in raw form. Once the insulation is sprayed into walls, it does a considerable job of blocking heat from flames, or from warm weather conditions [source: Wallender].

Windows, important for visibility and light, can nonetheless be a fire hazard. Even before a window is in direct contact with flames, the intense heat of a nearby fire can cause the glass to break. And a broken window allows flames to enter a building easily. In addition, the heat from a fire outside might be enough to simply ignite flammable items inside a home without direct contact.

To protect your house, consider installing fire-resistant windows. One example is dual-paned glass windows, which, in addition to providing energy efficiency, also double the time it would take for fire to break the windows. The outer layer will break first before the inner layer. Tempered glass, which is heat-treated to make it about four times stronger than regular glass, is also effective.

Though they don't provide visibility, glass blocks are extremely fire-resistant while still providing light. Perhaps the best is wired glass, which is tempered glass with metal wire reinforcement. Doors that require fire resistance but also visibility often incorporate wired glass windows.

It's also wise to note the importance of window framing. Steel framing offers the best fire protection, followed by wood and aluminum. Vinyl is the least effective.

Concrete, one of the most common building materials, is also an excellent fire-resistant material. It is noncombustible and has low thermal conductivity, meaning that it takes a long time for fire to affect its structural, load-bearing ability, and it protects from the spread of fire. It's actually significantly more fire-resistant than steel, and often used to reinforce and protect steel from fire.

However, it's important to note that not all concrete is created equal. It consists of cement and aggregate, and the particular kinds of aggregate materials used can vary, as well as the amount used. Aggregate can make up 60 to 80 percent of the concrete's volume {source: Ashley]. The exact fire-resistance properties change depending on the type and amount of aggregate used. Natural aggregates tend not to perform as well. Moisture in the aggregate can expand when heated, causing concrete to sinter after long exposure.

Concrete is often listed as among the best fire-resistant roofing materials, too. And you shouldn't overlook the roof as essential in fire-protection, since it's extremely vulnerable to sparks blown from wildland fire.

A more recent development in concrete construction is known as the Insulating Concrete Form (ICF). This structure is often used inside the walls of things like apartments and commercial buildings and consists of two polystyrene insulation panels with concrete poured between them. The completed material resembles a concrete sandwich, and is quick and cheap to construct, while offering a great balance of climate insulation, noise blocking and fire resistance [source: PCA].

Stucco is a plaster that has been used for centuries for both artistic and structural purposes. Modern stucco is made of Portland cement, sand and lime, and it serves as an excellent and durable fire-resistant finish material for buildings. It can cover any structural material, such as brick or wood. It usually consists of two or three coats over metal reinforcing mesh. A 1-inch (2.54-centimeter) layer of stucco can easily lend a one-hour fire rating to a wall or ceiling, meaning it will take one hour to catch fire [source: Nazarro].

Roof eaves (overhangs) are a fire hazard, but they can be protected with an encasement of fire-resistant material. Stucco is often recommended as one of the best materials for boxing in hazardous eaves.

Many structural materials will require underlying gypsum sheathing in order to achieve a good fire-resistant rating, and gypsum board is the most commonly used fire-resistant interior finish. Gypsum board, also known as drywall, consists of a layer of gypsum sandwiched between two sheets of paper. Type X gypsum board is specially treated with additives to further improve its fire-resistive qualities.

The paper on the exterior of the type X gypsum board burns slowly and doesn't contribute to fire spread. In addition, gypsum board has a noncombustible core that contains chemically combined water (in calcium sulfate). When affected by fire, the first thing that happens is that this water comes out as steam. This effectively impedes the transfer of heat through the gypsum board. And even after the water is gone, the gypsum core continues to resist fire penetration for a time. Builders often use multiple layers of gypsum board to increase the fire-resistance rating.

If we learned anything from the popular children's tale of the "Three Little Pigs," it's that you should make your house out of brick. This isn't such bad advice. Brick is not only resistant to a big bad wolf's huffing and puffing — it's also resistant to fires.

As bricks are made in a fire kiln, they're already highly resistant to fire. However, it's true that individual bricks are much more fire-resistant than a brick wall. A brick wall is held together with mortar, which is less effective. Nevertheless, brick is commonly cited as among the best building materials for fire protection [source: CLM]. Depending on the construction and thickness of the wall, a brick wall can achieve a one-hour to four-hour fire-resistance rating.

So, although some materials are more fire-resistant than others, several factors might influence a builder's decision, including cost effectiveness, ease of installation and climate.