Greening Your Siding

March 02, 2006
March/April 2006
A version of this article appears in the March/April 2006 issue of Home Energy Magazine.
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        When the siding/cladding decisions emerge in a green residential building project, we are all reminded that green building is a work in progress, and that it has a considerable way to go. In the early 1990s, a tool called Life Cycle Assessment (LCA) was developed originally for internal use by manufacturers considering options for product development. Most LCA studies today adhere to the principles laid out in a series of International Organization for Standardization (ISO) documents known as the 14040 Series within the broader ISO 14000 category on environmental management. LCA can be used to help decide whether a building material or system is truly green or sustainable.The idea is to look at its entire life cycle, from the mining or manufacture of the material to the end of its useful life, including such considerations as the transportation cost of moving the material from one place to another.The goal is to modify each phase of the life of a material or system so that it gradually gets closer and closer to the green or sustainable ideal.
        In my experience, there are three major cost considerations when building a green residential structure: roofing, siding, and flooring.The greener the products you use for these surfaces, the more likely it is that the costs for the home you are building will increase. If you upgrade from vinyl siding (the principal siding used in residential construction these days) to a cementitious or wood fiber siding, the cost of the siding can at least double.Vinyl siding is under fire from environmentalists for several reasons. These include manufacturing issues that affect the health of residents in the area where it is produced; potential hazards when it burns (giving off dioxins); and the lack of a comprehensive recycling plan at the postconsumer stage of its life cycle.Yet vinyl has proved to be the least costly siding to install. If installed properly it generates fewer problems than almost any other siding, and it gives many years of effective service, requiring no painting or expensive maintenance other than power washing from time to time.
        What are our siding options and what criteria do we use to make a choice, other than cost? In a previous article on exterior wall systems “Greening the Exterior Walls,” (Jan/Feb ’06, p.12) I briefly described aerated concrete and strawbale walls and explained that they do not require siding in the traditional sense. But they do require a coating—a kind of stucco—because the primary building material is vulnerable to moisture damage. The coatings for these materials must be extremely moisture resistant, because unlike other siding materials, coatings are responsible for keeping moisture out of the walls and permitting the wall to dry effectively when it does get wet.They require minimal maintenance once applied, and they can last the lifetime of the structure.The clay/sand/straw coating applied to strawbales is clearly an effective green alternative because the product is available at a local level and production costs are very low.At the end of its useful life, this coating can be placed back into the earth. There is, however, a high environmental cost in the form of CO2 emissions for the production of cement that is used in any cementitious product, including stucco.
        Cementitious siding has become the alternative choice to vinyl siding in residential construction, but it has other drawbacks besides CO2 emissions. Some concerns have been raised about the source of wood fibers used in some of these products. Cementitious siding comes fully primed and can come painted also; therefore it may not need to be painted, but it will probably require repainting in the future.This means that there will be some ongoing maintenance, although, since cementitious products do not expand and contract like wood, it will probably require repainting less often. If the cost of this product and its installation is double that of vinyl, and if it must be painted as well, it may be prohibitively expensive, especially for housing designed for low- or moderate- income families.
        Cementitious siding will not rot like wood when it gets wet; it is fire resistant; and it is recyclable. There is still some debate as to whether using furring strips under this siding as part of the rain screen would make it function more effectively over time and so reduce maintenance.
        Wood siding has been used for generations, but today it represents a very small portion of the siding market. Whether it be clapboards or shingles, finding wood products from certified forests can be a challenge. In addition, fully priming and painting poses two problems. When all surfaces of wood siding are not properly primed, it is more subject to warping and peeling; second, wood siding is more expensive to maintain when it is not properly primed and painted in the first place. Wood siding must constantly be repainted. It is always a good idea to use furring strips under wood siding during installation. Surfactants in the wood are known to compromise house wrap, causing moisture to penetrate through the house wrap and into the sheathing and wall cavities. Furring strips keep the siding from touching the house wrap, allowing any moisture that gets under the siding to dry to the air cavity created by the furring strips.This greatly reduces warping and peeling. For years, a panelized wood product called T-1-11 was used on exteriors. In its earlier incarnations, it was prone to delamination, and if flashings were not properly installed on the butt ends of two adjoining panels, the delamination potential was even greater. Apparently some improvements have been made in this product, and, if it is installed properly, wood siding could be a low-cost alternative to vinyl siding.
        Hardboard is a manufactured product made of reconstituted natural wood. It is created by reducing natural wood to fibers; adding resins, glues, and/or waxes; and pressing this compound into panels or clapboard siding.The early versions of hardboard failed when they were subjected to moisture conditions. Lawsuits filed against the manufacturers charged that it would exhibit thickness swelling, edge checking, physical degradation, buckling, surface welting, delamination, sponginess, wax bleed, and raised or popped fibers.These conditions would cause paint failure, which made the hardboard even more vulnerable to these various kinds of moisture damage.Manufacturers claim that they have solved these problems and that they now have a more durable product. Specifically, they claim that the bonding agents are much more effective. Because hardboard is made of recycled materials and is recyclable (if it is not painted or stained), it is an environmentally friendly product. It comes in the form of lap siding as well as panels. It is advisable to use furring strips under hardboard, which increases the cost of installation.
        Of two green homes that I recently monitored, one used a full brick veneer on the exterior and the other used a stone veneer. If these veneers are installed per manufacturer’s instructions, including proper flashings to drain water away from the back of the brick, and if proper rain screens are used for both, they can be very effective; but they are very expensive. Environmentally, they have excellent characteristics: they are reusable and recyclable; they will provide a durable surface; and they require minimal maintenance over many, many years.
        And so we return to our original dilemma. When we review all the options from a green building perspective, the least costly, most effective, and relatively long-term siding alternative is the vinyl product, but this product places the heaviest burden on the environment. Fortunately, the demand is growing for new siding materials that are environmentally friendly.With this increased demand, there is a greater possibility that the cost of these greener products will go down as well.
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