Concept or Reality?

Table 1. Siding Materials Costs
Siding Type	Cost*/Square**
Vinyl	$150
Aluminum	$180/ft2
Steel	$220/ft2
Composite/engineered board	$240-270
*1998 dollars **One "square" (one yd2) equals 9ft2

In recent years, the term "green building" has entered the vocabulary of the residential construction industry. How can it be interpreted? Are we in danger of tossing around these terms and concepts too casually? These are questions that aren't typically asked in the articles and news presented in each issue of Home Energy, so we are beginning a regular column here that will explore these issues. We hope it will initiate a little more thought about reconciling energy and resource conservation concepts with actual practices.

Green building practices can be described as practices that reduce the use of materials and energy in construction, lower occupants' consumption of energy and water, and minimize waste disposal in remodeling or demolition. This, of course, begs the question, In comparison to what? Standard methods are often wasteful and inefficient, and these methods are the starting point for making improvements--many of which have been labeled "green building".

Discussions of green building often involve the term "sustainability". This has been defined in several ways, but the United Nations has described sustainable practices as those that "meet the needs of people today without destroying the resources that will be needed by persons in the future ... ." This is well and good, but it is an impractical definition; Home Energy is devoted to practical building tips, and not knowing the future number of people or their life-styles makes it impossible to plan using this idea. However, green building practices may be able to help us achieve some environmental benefits on a real scale.

A new or remodeled green building will maximize the use of all construction materials and will minimize waste. It will incorporate as few nonrenewable and precious materials as possible. It will have appliances and devices installed that will minimize the use of both water and energy. Such a building will be durable and low-maintenance. It will be comfortable, and the quality of its indoor air will be high.

That said, it is possible that doing some of these things may still result in environmental damage. Life-cycle analysis examines the entire chain of activities of resource extraction, production, consumption, and disposal--including energy use, water use, and toxicity production--necessary for the use of construction materials. Full life-cycle analysis is beyond the scope of this column, but we will discuss this approach as topics warrant. And we will do the best we can to steer the reader toward good references and resources.

The best green building takes all of these life-cycle factors into account. Yet all good green building relies on integrated design and a systems approach to the building--recognizing, for example, that increased insulation will result in lower heating and cooling loads, and thus to downsizing related equipment. In fact, green building practices generally spend more on the human cost of design in order to reduce the costs of resource use.

If green building methods succeed in becoming common practices, perhaps the term will cease to have meaning. We have a long way to go before that happens, but that's the direction we're headed. Voluntary programs promoting green building practices have been started in many communities across the United States, where none existed prior to 1991 (see "Green Building Programs--A Growing Trend," HE, Jan/Feb '00, p. 34). The National Association of Home Builders (NAHB) has produced a guidebook to green building techniques and programs. Fannie Mae and the NAHB have started a joint effort to finance home mortgages for energy-efficient housing.

Still, this leaves sources like Home Energy to attend to the gritty details. I hope this column, as it unfolds, will contribute to bridging the gap between good intentions and common practice. We welcome comments, questions, and topic suggestions from readers and will begin here with an exploration of residential siding options.

Choosing Green Residential Siding

Historically, wood, brick, and stucco have been the materials of choice for the exterior of residential housing. For more than four decades, homeowners have been protecting their house exteriors and altering the look of their homes by buying and installing residential siding. Aluminum was the most common siding sold in the United States for nearly two decades. Vinyl siding caught on by the 1970s and has established a strong market. Consumers were faced with these two alternatives for years--and into the 1990s, vinyl was the most widely used type of siding.

This trend has undergone a shift in recent years. Consumers were given another option when steel was introduced as a more durable alternative to aluminum. And now a fourth type of siding is available: composite material. This is a composition of wood and cement, with resin used as a bonding agent. It is manufactured in preformed shapes.

All of these materials can be designed to look professional and can be formed with a woodlike grain. But let's compare them from an environmental standpoint.

Materials

For the materials themselves, both aluminum and steel exhibit good green traits. Both are made from recycled metals, and both can be recycled after replacement. Composite wood products are often made with shavings or sawdust, byproducts of other lumber production. Finally, while vinyl technically can be made with recycled resin, only a couple of brands actually are, and only the newer vinyl siding is recyclable.

Longevity

Durability and maintenance are other key environmental factors. All of these materials are more durable than wood siding, and they need much less maintenance. They seldom need to be painted--an advantage, considering the potential air pollution from most paints. Vinyl is colored throu-ghout and will not rot, rust, or peel: it is susceptible only to fading. However, vinyl is brittle in cold temperatures and thus could be damaged under some winter conditions; it can also buckle in excessive heat.

Aluminum or steel siding may fade, and they can oxidize under harsh conditions, but they are unlikely to require paint more often than every 20 years. One of the drawbacks of aluminum is that its paint can be scratched. Aluminum can also warp and it can be dented by a lawnmower edge or even by hailstones. Steel has proven to be a popular substitute for this reason (although its paint can also be scratched, and unless it is touched up, the steel could rust).

Composite materials are generally stronger, denser, and more crack resistant than ordinary wood (or vinyl, or aluminum), making them exceptionally durable. They resist normal deterioration, and some products are fire retardant.

All of these materials resist insects and fungus.

Labor and Energy Use

Metal siding has a lower embodied energy than vinyl or composite wood products because it uses recycled steel and aluminum. However, because steel can corrode and may be damaged if it is not carefully installed, it should be installed professionally. The other materials can be installed by the weekend carpenter, although specific guidelines should be followed for installing each one.

Energy efficiency is a separate matter. None of the materials has significant insulating capabilities. Vinyl siding is 0.04-0.048 inches thick, and aluminum ranges from 0.019 to 0.024 inches. Steel is comparable to vinyl. As a result, the R-values of all three materials are less than 1. Because vinyl follows the contour of walls very closely, backer board is sometimes sandwiched between the wall surface and the siding; this board adds a little insulating capability if it is installed correctly, but not much. Composite wood siding also adds a little insulation value, but only if it is used as siding rather than as the original wall surface.

Costs and Markets

Vinyl is by far the least expensive of the siding options. Of course, prices can vary dramatically among different regions, and installation costs vary even more (see Table 1). Environmental factors can vary among siding types, but regional markets often determine which one will be used. In the South, vinyl still rules because it is light, inexpensive, and easy to install, and it is not likely to be exposed to temperatures that render it brittle. In the Midwest, the steel siding market has proven to be robust because steel resists hail, tornadoes, and other extreme weather conditions. Thus much of the aluminum business has been squeezed out of that region. Composite siding is still unknown in many markets, but it is slowly becoming more well known.

The American consumer buys siding--like many other things--primarily on the basis of cost and aesthetics. These vary regionally, and thus help break the American siding market into smaller, more distinct markets. Yet environmental factors play an increasingly valid role and are likely to become more prominent with time.

Ed Wyatt is an assistant technical editor of Home Energy and an engineering consultant.

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