Hardboard and OSB Siding

Sep 1, 1999

Many manufacturers of hardboard and oriented strand board (OSB) siding have been hit with class-action lawsuits across the country.

Oriented-strand board (OSB) siding is made from wood strands that are oriented in layers under heat and pressure. The top layer is resin impregnated or protected with a sheet of resin-impregnated paper. Some OSB sidings also have factory-applied topcoat or primer. It can be painted or stained to suit your tastes.

In hardboard siding, wood fibers are oriented at random and bonded with a resin under heat and pressure. The result is a dense, tough material, somewhat less stable than plywood. To a greater degree than solid-wood siding, the durability of hardboard and OSB is dependent on proper installation and moisture control.

Both OSB and hardboard sidings are among the least expensive siding options and remain widely used, particularly in multi-unit development projects. The primary reasons for the plethora of lawsuits is buckling, swelling, and decay of siding. When subjected to moisture, hardboard expands more in length than a solid piece of wood does. This expansion from moisture absorption lies behind most hardboard siding failures. The hardboard industry standard allows an expansion of 2.4 inches for every 50 feet. This is enough to pull nail heads through a siding board as it bows outward. Breaks in the finish caused by pulled or overdriven nails, lack of paint protection on cut edges, or subjecting the siding to ground contact or water splash can invite more moisture absorption, causing more expansion, decay, and so on. According to the American Hardboard Association, hardboard fares worst in climates that have big swings in temperature and humidity and does best in areas that are dry year-round.

Identifying the manufacturer of problem hardboard or OSB siding may be difficult if documentation from the vendor, installer or manufacturer is not available. If no identifying marks or names on the back of the siding can be found, it may be necessary to identify the siding by the repetitive wood patterns on the face. Some sites identifying the characteristics of hardboard siding products are:

Interactive Resources has provided expert consulting and diagnostic architectural services for dozens of homeowners, developers and contractors involved in hardboard and OSB siding litigation.

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