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Composite siding is a building material used on the exterior of homes and commercial structures. Known as cladding, siding, or weatherboard in various parts of the world, this product protects the interior of a building from water and other exterior elements. It also serves an aesthetic role, and is available in a number of textures and materials to suit various decors and home designs.
Like other cladding products, composite siding is installed so that it covers the exterior of a building completely, providing no openings for water to enter the interior of the space. Siding is available in boards or planks, which can be layered over one another horizontally or vertically. It is also commonly sold in the form of shingles, or shakes, which are smaller tile-like sections that can be layered in a variety of patterns. Some composite siding products are sold in the form of large panels, which are mainly used on commercial buildings, or to cover soffits or trim sections on homes.
While siding has traditionally been made from cedar or pine, these materials can be expensive and also are susceptible to rot and termite damage. Composite siding costs much less than siding made from hardwoods, and offers an array of other benefits as well. Some varieties of composite siding are made from shredded wood or sawdust, with a bonding agent added for strength. Known as Oriented Strand Board (OSB), this product offers the look of solid wood siding for a fraction of the price. Like traditional wood products, OSB is susceptible to moisture damage, but offers a higher level of protection against termites and rot.
Fiber cement board is another popular composite siding product. Made from cellulose fibers, sand, and Portland cement, this material is one of the most durable and longest-lasting siding products on the market. It can be made to resemble wood, but is much cheaper and typically will outperform wood siding on a number of factors. Fiber cement board is highly resistant to fire, termites, and water damage, and holds it shape through the years with little maintenance. This product can be purchased in many different colors and finishes, and requires repainting only every ten years or so.
Despite its many benefits, fiber cement board also has a number of potential drawbacks. First, it is very heavy, which means longer and more difficult installation. Unlike wood siding, cement board can't hide irregularities in a building's framing, which can give the exterior walls a bumpy or wavy look. It is a poor thermal insulator, and does little to block sound transmission. Finally, the dust produced when cutting this composite siding product can cause respiratory irritation and illnesses.
I have observed composite siding types come and go for over 40 years. They are typically made from wood fibers, and when the backs or cut edges of panels are exposed to moisture vapor or liquid, they decay much faster than common untreated wood siding. They are much cheaper and highly dependent on precise installation according to the manufacturer's guide.
Cheaper and good workmanship are not ordinary bedfellows, so this precision almost never occurs, which is why in the real world, these products have seldom ever lasted even 20 years without significant degradation, swelling and decay.
Other than being inappropriate for exterior use, they are great!