Fiber cement siding, a construction material made from a blend of cement, silica sand, is used to cover the exterior walls of a home. This product is a popular alternative to traditional vinyl or wood siding due to its durability and strength. Most fiber cement products come with a warranty of up to 50 years, and are known for their resistance to fire, termites, and rot. Despite its many benefits, this material is also associated with a number of problems, ranging from adverse health effects to moisture damage.

New cottages with green grass near the road
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Image of cottages with cement fiber siding.

Asbestos

Fiber cement siding has been used for over a century to cover the exterior of homes. From its first use up through the 1980s, this product was often reinforced with asbestos fibers, which helped make the siding even more durable and resistant to fire. By the end of the 1980s, asbestos use was discontinued due to a link between asbestos fiber inhalation and lung cancer. Homes built before the late 1980s may have cement board siding that contains asbestos. This material is only harmful if the fibers are released through damage or removal of the siding. Intact fiber cement siding should be left as is, or removed by a professional abatement contractor. No holes should be drilled into the planks, and they should not be cleaned with pressure washers or abrasive tools.

Silica Dust

Modern cement board siding contains no asbestos, but it does contain a hidden health hazard. Cement siding is made from equal parts cement and silica sand, with a small amount of wood fibers and other elements. When the planks are cut during installation, silica dust is released into the air. This substance is extremely hazardous to the health, and can lead to respiratory problems or other illness. To minimize exposure to silica, cement board siding should be cut well away from other people. Installers should wear full respirators, as simple face masks are ineffective. Some installers may decide to wet the siding while cutting to keep dust contained.

Installation Difficulties

While fiber cement siding is prized for its strength and durability, these same features can be a problem during installation. One of the biggest problems is the difficulty in cutting these planks. While traditional wood or vinyl siding can be cut by hand, most fiber cement board requires the use of specialized saws designed for fiber cement. Once the boards are cut, they are often left with rough edges, which require filing or smoothing by hand. Fiber cement boards are also much heavier than other types of siding. This means installation is more labor intensive, with at least two installers needed to carry and hang each board.

Moisture

Fiber cement siding manufacturers have faced a number of class-action lawsuits from consumers whose homes suffered moisture-related problems. Because this material is more porous than vinyl, it can absorb water, especially through edges that have been cut during installation. This water can then cause the product to crack or split, especially in colder climates. Moisture infiltration can also cause mold or mildew growth in the framing members or sheathing. While wood siding also absorbs water, it dries out much faster than cement board, resulting in fewer problems.

Other Problems

Cement siding is considered a poor provider of thermal resistance. This means that cold or hot air from outside your home will penetrate this material fairly easily. Thermal resistance of a given material is indicated by a measurement called an R-value, with higher values equating to better levels of resistance. According to the Colorado Energy Board, cement board siding has an R-value of .34, which is nearly half that of uninsulated vinyl or aluminum. Another issue with fiber cement siding is its inability to block sound transmission through the walls. This means that more noise from the street activities will pass into the home.