Siding and Sheathing Options

While it is typically inadvisable to judge a book by its cover, it is undeniable that a building’s exterior wall surfaces are among its most visible and defining features. It is no short order, however, to choose an aesthetically appealing siding material that can stave off years of harsh weather, require minimal repainting or waterproofing, and optimize of substitute for wood. Some traditional building methods, such as rammed earth, create both interior and exterior surfaces along with the basic structure, without the need for additional materials. Most other building systems require a significant amount of siding and sheathing. Fortunately, there are some new choices.

This excerpt was reproduced with permission from Building with Vision: Optimizing and Finding Alternatives to Wood by Dan Imhoff. To purchase the book, please visit the Oikos Bookstore.

Siding
North America’s most popular siding has traditionally been solid wood, a regionally logical but problematic solution due to decades of overharvesting and the subsequent declining quality of materials. Vinyl siding (made primarily from polyvinyl chloride), long-lasting but often unattractive, is wood siding’s chief competitor. PVC is currently under attack by many environmental groups, including Greepeace, because of the persistent organic pollutants associated with PVC production, and many experts feel it has no place in a healthy structure. It is also difficult to recycle used vinyl siding into other siding products, and this has been rarely done except at the demonstration level. An increasing number of engineered wood paneling products bind either virgin or recovered wood fibers with some kind of formaldehyde-based resin. When using these products, investigate the potential for off-gasing as well as the sources of raw materials.

Another siding solution on the rise is fiber-cement, which blends wood fibers with Portland cement to create low-fuss, 50-year warrantied faux wood siding and roofing materials. Cement-based conventional stucco has provided a durable, low-maintenance siding option for some time, and in certain areas of the country, traditional earth and lime plasters are reemerging as an exterior finish surface. Metal sidings are high in embodied energy and production impacts, but they are also typically high in recycled content and recyclable. Some metal materials are being selectively integrated in green projects as siding options and even interior wall surfaces.

Solid Wood
Solid wood siding products such as bevel lap, ship lap, board-and-batten, and shakes have traditionally come from mature cedar, redwood, and other species that are extremely water-and insect-resistant. The most desirable and durable materials come from old-growth trees--making FSC-certified, recycled, or salvaged materials all viable green options.

On the positive side, wood is renewable, locally available in many regions, relatively low in embodied energy, and ultimately biodegradable. On the other hand, wood siding can require frequent maintenance, generate a fair amount of jobsite waste during construction, and be short-lived.

With the increase in FSC-certified acreage, however, and the intent of large retailers to stock certified building products, there should be an increasing supply of environmentally preferable wood siding options available to builders on a regional basis (see page 38 for a list of websites). FSC-certified composites also should gradually become more available, as the market matures. In Spring 2001, Collins Pine announced the availability of TruWood, an FSC-certified hardboard siding material.

Fiber-Cement
Increasing in availability are siding systems in the form of smooth and textural panels, planks, and shingles that combine Portland cement with wood fibers to simulate wood. Green builders are turning to these products because of their relatively low cost and projected longevity. Many have 50-year guarantees, although there are no existing track records to show if they will actually last that long. A significant drawback to fiber-cement is the current sourcing of wood fiber used in some of these products. Apparently, only a handful of species’ fibers can tolerate both the hot temperatures generated during processing and the extreme alkalinity of the cement; and those species aren’t being harvested on this continent. For example, James Hardie, an Australia-based company and leading supplier of fiber-cement siding, obtains its wood from Australia and New Zealand. Considering the energy-intensiveness of cement manufacture and the overseas transportation of wood fibers (not to mention their uncertified harvesting origins), fiber-cement siding does carry a high embodied energy burden. Perhaps regional sources of fiber will soon be identified to make this a more resourceful option.

Sheathing and Wallboard
Among a conventional building’s most wood-intensive components are the panels for sheathing exterior walls, floors, and roofs. Since the 1930s, the lion’s share of sheathing has been supplied by plywood, although oriented strand board (OSB) has been rapidly gaining since its introduction in the 1980s. For some time, however, a still small but growing diversification away from sole dependence on virgin wood materials for siding and sheathing options has been underway. Today, recycled newsprint, recovered wood waste, byproducts of power incineration (synthetic gypsum), and agricultural fibers are making their way to structural and nonstructural sheathing and other panel products. Some can serve as subfloors and roof decking as well.

Straw Board
Despite a huge production potential across the heartland of North America, the supply of panel board products made from agricultural residues such as straw and sugar cane has been anything but abundant. In late 2000, Mankato, Minnesota-based Phenix Biocomposites introduced a competitively priced, structural strength board made from wheat and soybean straw as a sheathing alternative to plywood and OSB. (See pages 112-115, 118 for more details.) As a board material, straw has some inherent advantages. The microstrands of the fibers reduce the amount of binder necessary for production. Straw boards can also be more water-resistant than wood-based panels.

Color Recycled Papers
Each day in northwestern New Jersey, between 150 and 200 tons of newspapers from the surrounding region are turned into sound-deadening acoustical fiberboards, packaging, and other products at the Homasote manufacturing facility. The (non-deinked) newspaper fibers are bound together with a wax emulsion to produce egg carton-like,grey boards in a variety of thicknesses and densities. As a resilient, highly insulative carpet underlayment system, the recycled newsprint board competes with a combination gypcrete and plywood subfloor system. Structural roofing panels fromt he same materials are also available. Because it has proven remarkably weather-resistant, Homasote board is also being promoted for use as exterior sheathing and is frequently used to fill expansion joints in concrete sidewalks.

For more than 25 years, Simplex Products (now Ludlow Coated Products) in Adrian, Michigan, has been producing thin but remarkably strong panels of 100 percent recycled paper waste (80 percent post-consumer content) that offer superior racking and shear strength. The product literature claims that their structural grade Thermo-ply sheathing can save up to six trees on a standard house. Energy savings are also touted--a building wrapped with the foil-faced boards (with corners overlapped) can produce and extremely tight seal. According to Ann Arbor architect John Barrie, Thermo-ply sheathing has excellent racking strength and is an economical choice for fiber-cement and vinyl-sided homes, among other applications.

Sources for these products can be found in the Oikos Product Directory.