Fiber cement siding is made from a blend of cement, silica sand, wood fiber and other ingredients, making it a siding option that is known for durability and strength. Most fiber cement products come with a warranty of up to 50 years, thanks to a natural resistance to fire, termites and rot. Despite its many benefits, fiber cement siding comes with its share of problems, ranging from adverse health effects to moisture damage.
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Asbestos Content in Older Siding
Fiber cement siding use spans back for over a century. Until the 1980s, this type of siding often included asbestos fibers for reinforcement, which helped make the siding even more durable and resistant to fire. By the end of the 1980s, manufacturers stopped using asbestos because asbestos fiber inhalation is linked to 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. If you suspect your old siding has asbestos in it, keep the siding intact, or have it removed by a professional abatement contractor. Avoid drilling holes, cleaning with a pressure washer or using abrasive tools on fiber concrete siding that may contain asbestos.
Silica Dust Issues
Modern cement board siding contains no asbestos, but it does contain a hidden health hazard: silica dust. Cutting the planks during installation releases silica dust 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, cut cement board siding away from 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.
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 the planks. While traditional wood or vinyl siding can be cut by hand, most fiber cement board requires specialized saws designed for the material. Once cut, the boards often have 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.
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 the cut edges. This water can then cause the product to crack or split, especially in colder climates. Moisture can also cause mold or mildew growth in the framing or sheathing. While wood siding also absorbs water, it dries out much faster than cement board, so it's less of an issue.
Cement siding is considered a poor thermal insulator. This means that cold or hot air from outside your home penetrates this material fairly easily, so it doesn't help insulate your home. The R-value of a product describes its thermal resistance, with higher values equating to better levels of resistance. Cement board siding has an R-value of 0.34, 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, which means you may hear more outdoor sounds inside your home.
The nature of fiber cement siding lends itself to some issues in performance. This type of siding tends to be brittle. It can break or crack easily, especially during the installation process. Damage can also happen if something hits the siding hard after installation.
Shrinking is another potential performance issue. The siding cures and shrinks some after installation. If it's installed properly, that shrinking isn't an issue. If not, the shrinking may leave your home looking unattractive. Moisture and temperature changes can also cause shrinking of the siding.
Fiber cement siding also requires more maintenance than some other siding materials. You need to repaint the siding periodically. You also need to check the caulked seams on the siding every year. The caulk often loosens in five to 15 years, so you may have to redo the caulking.