Decisions about siding are consistently among the most difficult for environmentally concerned designers and builders of residential and light commercial buildings. Siding products must withstand all types of weather, look attractive both from a distance and up close, and be affordable to buy and install. With these demands in mind, which are the best products from an environmental standpoint? How do you balance the resource depletion concerns of using old-growth cedar with the life-cycle pollution concerns of PVC and the maintenance and durability concerns with the many available alternatives?
This article won’t offer all of the answers, but it will help you sort out the various pros and cons of siding options relative to the environment. Included in the discussion are wood sidings (cedar, redwood, spruce, and other softwoods), hardboard sidings, oriented-strand board (OSB) sidings, vinyl (PVC) sidings, aluminum siding, stucco, and fiber-cement sidings. Not addressed here are masonry sidings, including brick and face stone.
Examining the Options for Residential Siding
With any given building material, there are various life-cycle issues to consider. These were presented as a hierarchy of issues in the article “Material Selection: Tools, Resources, and Techniques for Choosing Green” in EBN Vol. 6, No. 1. If we apply that hierarchy to siding material selection (see checklist) we find that two of the most common areas of concern with building materials do not apply to a significant extent: impact on building energy use, and occupant health. The other life-cycle concerns outlined in the EBN material selection hierarchy vary widely for the different materials, as noted in the figure below. A more thorough analysis would make use of this material selection hierarchy separately for each siding option.
The wood species most commonly used for siding include western red cedar, redwood, cypress, northern white cedar, and eastern white pine. A few other species, such as eastern spruce and lodgepole pine, are used on a more limited basis. The most common wood siding products include bevel lap siding, shiplap, board-and-batten, and shingles. Primary environmental considerations with wood siding include the wood source (whether it comes from well-managed, sustained-yield forests), overall durability or longevity, and treatment requirements (painting, staining, etc.).
As a building material, wood has inherent environmental advantages: it is renewable; the forests where it is grown can provide diverse ecological habitat; it is energy-efficient to produce, relying ultimately on the sun’s energy through photosynthesis; there is very little waste associated with milling since waste wood is typically used for other manufactured wood products; it is often reusable; and it is biodegradable at the end of its useful life. There are tremendous differences, however, in how forests are managed. Many forest operations are not close to sustainable, resulting in soil erosion, loss of species diversity, and other environmental concerns.
To ensure that wood siding materials are environmentally responsible, we should look for products that are independently certified as coming from well-managed forests. Scientific Certification Systems (SCS) in Oakland, California and the Smart Wood Program of the Rainforest Alliance in New York City both offer services certifying private forest operations. Independent forestry experts are brought in to examine forestry practices of the company and determine if those practices meet the agency’s standards, which must conform to guidelines developed by the Forest Stewardship Council. A chain-of-custody process is then used to certify wood products coming from those certified forests.
Currently, there are very few third-party-certified wood siding products. Certified siding is produced by the Menominee Tribal Enterprises, in Neopit, Wisconsin, including bevel siding, shiplap siding, and log cabin siding (which offers a log cabin look). Eastern white pine is the primary species used for siding, though some eastern hemlock is also used. The bevel siding is produced in 6” and 8” (150 and 200 mm) widths and is thicker than standard bevel siding. Menominee wood products are sold nationally and can be ordered directly by lumber yards or end-users if a large enough order is provided to make the shipping economical.
Seven Islands Land Company in Maine sells certified northern white cedar to the Maibec Company in Quebec, which mills white cedar shingles. These are often used for siding, particularly in coastal New England. Certified shingles from Maibec cost no more than their standard shingles, but unfortunately the company does not fully appreciate the potential marketing advantages of certified shingles and often does not differentiate them to buyers. Maibec produces about 50,000 squares (465,000 m2) of certified white cedar shingles annually, according to Tom Goodyear of Seven Islands. Until Maibec begins receiving specific requests for certified product, they are unlikely to actively promote the product.
Quarter-sawn spruce bevel lap siding could also be chain-of-custody certified from Seven Islands wood. This product is made by Ward Clapboard Mill, a small family business, using some timber from Seven Islands, but Ward Clapboard has so far not chosen to invest in the chain-of-custody certification. It is also possible that a certified white cedar lap siding could be produced from Seven Islands wood at some point in the future. Goodyear believes that this would be an attractive product.
The recently certified Big Creek Lumber Company in Davenport, California (see EBN Vol. 5, No. 6) may in the future produce redwood siding, but their initial focus is on decking. EBN is not aware of any certified sources of western red cedar, but red cedar shingles are often made from logs that are damaged during logging and wouldn’t be suitable for other lumber products.
APA-rated plywood siding
One of the lowest-cost siding alternatives is textured plywood that serves as both the sheathing and siding. Various textures are available to simulate more traditional siding alternatives. The most common of these is APA Texture One Eleven® or T-1-11, which has vertical grooves routed into the panels. The APA Sturd-I-Wall® system is a construction system in which APA-rated siding panels are attached directly to the wall studs or installed over non-structural sheathing (fiberboard, gypsum, or insulating sheathing). Plywood is rated by APA for vertical siding applications either 24” on-center (o.c.) or 16” o.c.
From a resource standpoint, plywood requires higher-quality logs than OSB, which can be produced from very small, low-grade trees. In general, logs for plywood must be at least 10” (250 mm) in diameter. However, the ability to have one material serve as both the sheathing and siding has significant resource advantages, as long as the wall system is adequately protected against water penetration. Nearly all plywood siding is produced with phenol-formaldehyde resin, which comprises about 11⁄2% of the finished product, by weight. Various pollutants result from the drying of plywood veneers (see EBN Vol. 1, No. 2), though tighter pollution control regulations in the past few decades have greatly reduced these emissions.
Oriented-strand board (OSB) siding has been in the news quite a bit over the past few years, due to widely publicized performance problems. OSB siding was first introduced in 1985 by Louisiana-Pacific Corporation (L-P), which today is the only manufacturer. The Masonite Corporation also produced an OSB siding product called OmniWood for a number of years, but that was discontinued at the end of 1996. L-P’s Inner-Seal® lap siding was a good seller for quite a few years as a lower-cost alternative to cedar. By 1996, Inner-Seal siding had been installed on some 800,000 homes nationwide.
Over time the product was plagued with widespread failures, however. In a May 1995 class-action lawsuit, which was filed in the U.S. District Court in Portland, Oregon, plaintiffs claimed that the siding was swelling, warping, disintegrating, and even growing mushrooms. A settlement was reached in which L-P has pledged up to $375 million to repair siding that was installed prior to January 1, 1996 (see EBN Vol. 4, No. 6). In June of this year, L-P turned the corner on their OSB siding fiasco, with the introduction of the Smart-Start line of siding and exterior products (see review). If performance can be improved with OSB siding, it may be preferable environmentally to many other siding products. OSB represents a more efficient use of the forest resource than solid wood, though the rapid expansion of industries using lower-quality wood fibers is stressing even that resource base.
Like OSB, hardboard siding is produced from low-grade trees. The product is generally made from material left over after higher-value wood has been claimed for other uses. Some of this material tends to be edge slabs and other waste from sawmills, but most is from whole trees. Major producers of hardboard siding include Masonite, Georgia-Pacific, ABT Building Products Company (ABTCo), and Temple-Inland Forest Products.
Tom Roe, hardboard and fiber-cement product manager for ABTCo, told EBN that their hardboard siding is produced from a mix of roughly 50% oak, 35% mixed hardwoods, and 25% pine, all from within a 50-mile (80 km) radius of their plant in North Carolina. The wood chips are fiberized and laid in a mat. Phenol formaldehyde (PF), paraffin and alum are added, and this mat is covered with a linseed-oil-saturated paper overlay. The mat is then compressed under high temperature and baked for eight hours at 350°F (180°C). Such a long baking process is unusual in the industry. It causes the natural lignins in the wood to bond, allowing ABTCo to use less than 1% PF resin by weight, whereas roughly 2% is typical. Whether the added fuel use and air pollution from the baking are preferable to the use of slightly more resin is debatable, however.
While ABTCo has had very few warranty claims on their hardboard siding product, several other manufacturers have not been so fortunate. Masonite Corporation is the target of a class action suit in Alabama. Plaintiffs claim that the siding “prematurely rots, buckles, cracks, and otherwise delaminates when exposed to normal weather conditions,” and a jury in the initial phase found that the product is “defective because it is unreasonably prone to failure.” The case is now in mediation, but it could return to the court if no agreement is reached.
While Masonite’s case is the broadest, other hardboard siding products have also had durability problems. The pressed wood fibers expand if they get wet, so the siding has to be properly protected from moisture penetration. This requires proper installation, including spacing the siding for slight expansion, caulking butt joints and edges, and properly painting the siding. Roe of ABTCo claims that properly painting wood and hardboard siding really requires brush application—with paint sprayers you can’t get a thick enough protective coat on the drip edge without risking runs on the siding face. Regular repainting is needed to maintain a 2.5 mil (0.06 mm) layer.
To reduce risk of moisture penetration, some siding manufacturers have used a composite with a very high percentage of synthetic resin. Werzalit of America, Inc. in Brad-ford, Pennsylvania, a subsidiary of Werzalit AG & Company of Germany, produces an advanced engineered siding that is a composite comprised of 21-25% melamine resin. Most of the rest is wood dust from Pennsylvania hardwoods. The siding is made in a die-form press, which compresses the product to a 60 lb/ft3 (980 kg/m3) density under high temperature. Then a baked acrylic finish is applied at the factory.
Even with high resin content, the Werzalit product has been known to absorb moisture and expand if it remains in contact with water, according to Betsy Pettit of Building Science Corporation. To prevent this problem, the company provides 1⁄4” x 11⁄2” (6 x 38 mm) ventilation spacers made out of recycled PVC for the horizontal siding. For vertical siding, Werzalit recommends installation over 3⁄4” (19 mm) wood furring strips. Installed as recommended, Werzalit siding has a 20-year warranty, including 15 years for the painted surface. The only maintenance suggested is periodic wash-down of the siding with mild, soapy water.
Another wood-resin composite siding is produced by Smurfit Newsprint Company in Oregon City, Oregon. Their Cladwood® product has a phenol-formaldehyde-bonded particleboard substrate with a resin-impregnated, fairly thick, recycled-paper overlay on both sides. According to Mike Hibbs of the company, the recycled content ranges from 16% to 26% by weight, including about 10% post-consumer recycled newspaper. Hemlock and fir sawdust and wood shavings comprise most of the rest of the product. Cladwood is produced in panels with various styles of imprinted grooves to simulate vertical wood siding. Finishing with paint or stain is required. Cost is comparable to hardboard siding, and the company offers a 20-year warranty.
Extruded aluminum siding at one time held the bulk of the non-wood siding market. Introduced in the 1940s, it was originally sold with a natural aluminum finish, but soon after introduction became available with far more popular enameled finishes, offering a variety of color choices. Advantages were low maintenance, good durability, resistance to corrosion or deterioration, light weight, and minimal need for repainting. Problems include denting and relatively high cost, compared with PVC (vinyl). PVC siding has now almost entirely forced aluminum from the market. Even industry leader Alcoa, which still manufactures aluminum siding, promotes its vinyl siding far more heavily.
Polyvinyl chloride (PVC) or vinyl siding was introduced in the 1950s and has gradually gained market share—first from the aluminum siding market and more recently from wood siding. Today, more vinyl siding is produced than any other type of residential siding (see graph: U.S. Market Share...). In 1995, more than 3 billion square feet (279 million m2) of siding were produced in the United States by some two dozen companies.
Vinyl siding has numerous advantages. It is inexpensive, easy to install (even over existing siding), virtually maintenance-free, and generally quite durable—some products have transferable 50-year or lifetime warranties. It is available in a wide assortment of colors (most of which are light to minimize solar absorption and material/color degradation), various profile designs, and textures ranging from smooth to rustic cedar. Some products have fiberglass rod inserts to increase the strength and keep the siding flat even on wavy walls. A wide assortment of PVC trim products are provided by manufacturers for finishing walls.
While many consider vinyl siding to be an almost ideal material, others are calling for the phase-out of PVC as a building material, citing environmental concerns associated with PVC manufacture and disposal. The environmental organization Greenpeace has been leading the fight against PVC and other industrial chlorine uses.
In the United States, roughly 11 billion pounds (5 billion kg) of PVC are produced annually. In the manufacturing process, chlorine is reacted with ethylene (from fossil fuel sources) to produce ethylene dichloride (EDC). The EDC is then synthesized into vinyl chloride gas, which is polymerized into PVC. Of these two intermediary compounds, both are considered health hazards, and vinyl chloride is listed as one of 24 “known carcinogens” in the U.S. Government’s Seventh Annual Report on Carcinogens . While release of these compounds into the environment has been dramatically reduced by the PVC industry, wayward emissions are still considered a problem by some. More significant, however, are concerns about dioxins and other organochlorines that may be created and released into the environment both during manufacture and incineration of PVC.
Certain dioxins, polychlorinated biphenols (PCBs), and other organochlorines are not only significant toxins, but they are believed to interrupt the endocrine system in humans and other animals. As publicized in the book Our Stolen Future (see EBN Vol. 5, No. 6), these endocrine disrupters are a very significant problem today. The bottom line is that vinyl building products carry significant environmental burdens.
Stucco differs from other products discussed here because it is troweled or sprayed onto the wall, rather than being attached in rigid pieces. Traditional stucco is cement-based plaster—a mixture of Portland cement, lime, sand, and water, with a few potential additives. It is applied in three coats: a scratch coat, base coat, and finish coat, for a total thickness of about 3⁄4” (18 mm). On a solid masonry or concrete wall, the scratch coat is not needed, as the masonry surface itself provides an adequate base.
More common in conventional wood-frame construction is
synthetic stucco, in which a polymer base replaces the cement and lime. The base may contain varying amounts and types of acrylic or butyl resins. Synthetic stucco is often applied over expanded polystyrene (EPS) insulation, as part of an exterior insulation and finish (EIFS) system. It typically uses two coats: a base coat, in which a thin fiberglass mesh is embedded, and a finish or color coat. The total thickness of the stucco coating is typically between 1⁄16” and 1⁄8” (2-3 mm) according to Marty Ellrick of El Rey Stucco Company in Albuquerque, New Mexico. Synthetic stucco remains somewhat flexible after curing, so it is less prone to cracking than traditional stucco. As a thinner coat, however, it is more prone to impact damage. The best synthetic stuccos have an elastomeric base with high acrylic content. Blurring the distinction between these two types are traditional stucco mixes with polymer additives, and synthetic top coats on a thick, traditional base.
While stucco can be painted, one of its advantages is that the integral color in the top coat makes periodic recoating unnecessary. After a surface has been painted, the coating must be maintained to stay attractive. From a resource perspective, the cement and lime in traditional stucco make it fairly energy intensive, but it provides a long-lasting, relatively maintenance-free surface. On a solid masonry surface, stucco is a logical choice for exterior finish. The acrylic and other resins in synthetic stucco carry the baggage of toxins and emissions from the petrochemical industry. These are not unlike conventional paint products, however, and they don’t require periodic reapplication like paint. There are durability questions about the thin surface created by synthetic stucco, however. Synthetic stucco is less moisture-permeable than traditional stucco, a factor that may contribute to moisture problems in some EIFS wall systems. A more significant problem is that a stucco wall often may not receive adequate flashing and drainage detailing to prevent bulk water problems.
A more recent entrant into the U.S. residential siding market is fiber-cement. This product is a composite material made of Portland cement, sand, wood fiber, and clay. Australia-based James Hardie Building Products has long dominated the fiber-cement siding market in the U.S., with some competition from F.C.P., Inc. (whose product was distributed until recently by Eternit) and MaxiTile, the latter imported from Mexico. This limited sphere is now expanding quickly, however, as hardboard siding companies get into the fiber-cement market. ABTCo has just started up a large plant and is selling the siding through its network of independent distributors. And a joint venture between Temple-Inland and Canadian fiber-cement roofing manufacturer ReCon Building Products has just broken ground on a plant in Texas, to be operational by May 1998, according to Temple-Inland’s Steven Raley.
All domestic fiber-cement siding products are 5⁄16” (8 mm) thick and come in smooth and various wood-grain textures. Lap siding is available in several widths from these manufacturers, and 48”-wide (1.2 m) panel siding is also available from James Hardie and ABTCo, including products with a stucco texture.
The fiber-cement products on the market today are direct descendants of asbestos-cement building products (siding and shingles) that were widely sold until the 1970s. The difference is that while asbestos-cement products used inorganic asbestos fibers as the reinforcement, today’s fiber-cement products use wood. (Asbestos
has been eliminated from most building materials because the fibers have been proven to be carcinogenic.) Not just any wood fiber can be used, however. The wood fibers, which comprise 8-10% of the material according to Tom Roe of ABTCo, have to be both durable and resistant to the high-temperature autoclaving process during manufacture and the alkalinity (high pH) of the cement. ABTCo uses wood fiber obtained from Russia, and Hardie uses wood fiber from New Zealand. The primary environmental burden of fiber-cement is embodied energy: both from the cement (see EBN Vol. 2, No. 2) and from the imported wood fiber.
Because today’s fiber-cement products are thicker and less brittle than the older asbestos-cement products, Tom Roe of ABTCo believes that it will actually be more durable, but it has not yet been around long enough to know for sure. ABTCo, James Hardie, and F.C.P. all offer 50-year warranties of their fiber-cement products.
Installation recommendations vary from manufacturer to manufacturer, but most call for leaving a 1⁄8” (3 mm) gap where the siding abuts trim, then caulking the gap. Butt joints can be loose (up to a 1⁄8” gap is optional—if a gap is provided, caulking is recommended). Because fiber-cement is porous and able to absorb moisture, it has to be painted or stained for weather resistance. (Moisture absorption and subsequent freeze-thaw conditions have proved to be a problem with fiber-cement roofing shingles in cold climates.) Some suppliers provide fiber-cement siding that is pre-primed or even pre-painted.
Long-term experience does not yet exist with fiber-cement siding, but experts EBN spoke with suspect that the frequency of repainting required should be lower than for wood. This is because the material should expand and contract less with absorption and loss of moisture. In the Southeast, wood siding often has to be repainted every three to five years; if the span of time before repainting can be stretched to 10-15 years, significant long-term environmental benefits will be achieved. Most manufacturers recommend a high-quality, exterior-grade 100% acrylic paint for fiber-cement.
Selection of siding is a complex decision relative to the environment. Depending on the material, there are four primary areas of environmental impact: resource concerns; lifecycle pollution impacts; the need for on-going painting; and durability. It is also necessary, of course, to balance these environmental concerns with such issues as price, ease of installation, and aesthetics. If wood from certified well-managed forests is available, that is an attractive choice. The need for frequent recoating with paint or stain remains a drawback, however. As more fiber-cement products are entering the market and the price is dropping, these may often be the most attractive option. With any product, durability depends in part on how the siding is installed. The table on page 15 summarizes the environmental pros and cons of different siding materials and should help you pick the best product for your needs.