Material Science: Selecting Building Materials

Part I: Overview — Introduction to Green Building

Part II: Land Use Planning — Creating Value, Protecting the Environment

Part III: Material Science — New Options in Eco-friendly (and Healthier!) Building Materials

Part IV: Be a Miser — Strategies for Slashing Your Energy Consumption

Part V: A Drop in the Bucket — Painless Ways to Reduce Your Water Use

Part VI: Breathe Easy — Controlling Pollution Inside Your Home

Part VII: Xeriscaping — Drought-resistant, Low-maintenance Landscaping

Part VIII: Greening America — Green Certification and a Look at the Costs

Green building — or sustainable building — is a complex process that begins with the development of the land that will become the community of homes, shops, schools, offices and parks. When the actual construction begins, the next challenge green builders will be faced with is the myriad choices in building materials. Their goal, whenever possible, is to select materials that have a minimum environmental impact over their lifespan, not only in terms of protecting and conserving natural resources, but also in respect to preserving a healthy indoor environment.

What makes building material green?

The primary factors to consider are: the resource efficiency of raw materials, indoor air quality, energy efficiency and water conservation. There are often trade-offs between the different goals of green building. Engineered wood flooring, for instance is a highly durable building material that efficiently utilizes every part of the tree, but the adhesive compounds used to construct this material can contain high levels of formaldehyde, a toxic volatile organic compound (VOC), "It’s a little like Physics 101," says Kevin Nelson of Stock Building Supply, a Triangle building supply outlet that has instituted its own green-materials certification program under the supervision of Southern Energy management. "You gain one benefit but take away another." Fortunately, as interest in and understanding of the benefits of green building has grown, manufacturers are now, more than ever, working to develop new technologies in accordance with green building principles. Indeed, engineered wood flooring is now available with a low formaldehyde content.

Efficiency is Key

Building and construction activities worldwide consume some three billion tons of raw materials each year, approximately 40% of total global use. Integrating green building materials into building projects helps to reduce this consumption, not only of the raw materials — wood, steel, concrete and more — but also all of the resources required to take that material from the forest or the mine to its end-use at the building site. Consider the total environmental costs of extraction, transport, processing, fabrication and installation, and ultimately, disposal.

Resource efficiency can take many forms. The durability of a building material determines how often it must be replaced, an important factor in reducing both raw-material consumption and waste creation. A building material that lasts 50 years, as opposed to 10, by its very nature, requires fewer resources and has a lower environmental impact. Like many green-building principles, durability serves not only to reduce environmental impact, but also offers the homeowner the added benefit of low maintenance.

Concrete masonry construction is a prime example of an extremely durable building material. Because walls and foundation systems are bound together as one solid unit with reinforcing steel, a concrete framed home is highly wind resistant, able to withstand hurricanes and, in some instances, even tornadoes. Concrete masonry offers no food source for termites, eliminating the destruction an infestation can cause, as well as the need for costly and potentially toxic ongoing termite treatments. Concrete won't rot or decay and is fire and water resistant as well.  "From a builder's perspective, a concrete masonry wall system creates an envelope that does not flex in high winds as a traditional wood-framed home can," says Paul LaVene, president of the Carolinas Concrete Masonry Association. "This translates to real tangibles like fewer cracks in sheetrock and nail pops."

Oriented Strand Board  (OSB) is considered a positive use of wood resources because of its strength and durability and its source in fast growing trees, like aspens. "We are seeing growing demand for products like OSB and Hardie siding," says Roper Brothers Lumber general manager Scott Warren. Hardiplank is the brand name for mineral-fiber siding manufactured by the James Hardie company. These products are available in lap siding, sheets, shingles and trim designs. Similar products are available from other manufacturers. Mineral-fiber or cement-based siding products are inexpensive and very durable. They are considered sustainable because of their extremely long life span.

Building materials that are manufactured with resource efficient processes capitalize on the economies of scale that can be achieved through plant manufacturing, rather than onsite construction —  reducing both waste and degradation of the building site. Pre-cut floor and roof framing packages minimize waste and can be scheduled for just-in-time delivery, reducing site disturbance.

Panelized wall and roof framing systems benefit from efficient use of materials, automated cutting and fastening methods and assembly in an environment protected from the elements. Structural panels replace the standard stud-insulation-sheathing wall system and are typically two outer layers of structural sheathing material, separated by an insulated core. One such product, Structural insulated panels (SIPs) are constructed of oriented strand board (OSB) sandwiched around an insulating core of expanded polystyrene foam (EPS). "These panels can be as large as eight feet by 24 feet and are available in a variety of thicknesses," says Alternative Building System's Michael Dilettoso. "And the creation of a more continuous insulating envelope — without stud penetrations — results in a more constant R-value throughout the entire shell of the structure."

Another wall panel system, AAC (autoclaved aerated concrete) consists of pre-cast panels of lightweight concrete. This building material, widely used across Europe and Asia for more than 75 years, is manufactured through a process combining sand, cement, lime, water and aluminum powder. Millions of embedded tiny bubbles make these concrete panels lightweight and also act as highly effective insulation pockets. Yet AAC is strong enough to withstand winds of 200 miles per hour, and like concrete block, withstands fire, flood and termites. "AAC is 75% air by volume", says Alternative Building System's Dilettoso, "so it is half the weight of concrete, meaning you can further conserve resources by downsizing footings and slabs." The design flexibility of AAC is exceptional as well, allowing for arches, ellipses, stucco siding, lap siding, cedar shake or brick.

ZIP system roof is a structural panel made by Huber Engineered Woods with a built-in moisture resistant barrier that eliminates the need for felt paper and H-clips. "The joints of ZIP sheathing are taped with a special tape, offering better moisture resistance for seams, valleys and ridges," says Roper Brothers Lumber general manager Scott Warren. "This plant manufacturing process requires fewer resources and also allows for easier, faster installation." Because the breathable moisture barrier is integral to the sheathing, it can't blow off, making it a more durable choice too.

Building materials that are factory finished and require no additional onsite priming or painting are also considered a more efficient use of resources. Pigmented and stamped concrete, pre-finished siding (like Hardiplank) and windows with finished surfaces offer the green advantages of plant-manufacturing efficiencies as well as greater durability.

Engineered wood floors use more of the tree than solid hardwood floor and, because of their construction alternating layers of lengthwise and crosswise grain, are considered more dimensionally stable. In addition, their UV-cured polyurethane and aluminum oxide finishes feature outstanding wearabilty, many with a 25-year guaranty.

Building materials can be considered green if they are constructed from locally available, indigenous materials because transportation and processing requirements are minimized. Typically at least 10% of  these materials would have to be extracted and manufactured within a 300-mile radius  (or a 100-mile radius if shipped by rail) to be considered local for green purposes. Often, the concrete block used in concrete masonry construction is manufactured from locally available materials.

Renew, reuse

Renewable resources are always the preferred green choice over finite, dwindling non-renewable resources. Materials manufactured from agricultural by-products or rapidly regenerating sources such as soy-based insulation, cork floors or bamboo floors or cabinets. Bamboo, for example, is a quick growing grass found throughout most of Southeast Asia that reaches harvesting maturity in only three to five years. It is 58% more stable than red oak and is used to manufacture a wide variety of building materials.

When it comes to wood-based products, green builders choose materials from a source certified to practice responsible forestry practices. Certification programs, such as the Forest Stewardship Council (FSC), The Sustainable Forestry Initiative or the American Tree Farm System act as independent watchdogs, verifying that, from the forest to the building site, including all successive stages of processing, manufacturing and distribution, a wood product was produced following guidelines for sustainable, responsible forest management. Over the past 12 years, the FSC has certified thousands of wood products from more than 82 countries.

Incorporating building materials with recycled content is another strategy for resource efficiency. Clay brick is typically manufactured with a variety of recycled materials, averaging 7% by weight. Cellulose insulation can contain as much as 85% recycled paper stock content, and fiberglass insulation 25% post- and pre-consumer recyclables.

"We carry carpet that is produced from 100% recycled materials and also offers adhesives with low VOC emissions," says Stock Building Supply's Kevin Nelson. " This recycled carpeting is derived primarily from post-consumer plastic soft drink bottles and is priced similarly with other carpet choices.

Recycled content tile is made from a high percentage of waste glass, from such sources as light bulbs and automobile windshields.

Salvaged building materials are another form of recycling that not only reduces natural resource depletion, but can also add character to a home. Reclaimed wood flooring is often derived from remilled salvage timbers. It can also be recovered from old flooring. From an environmental standpoint, this approach saves materials from the waste stream and does not impact living trees. Wood flooring is also available from trees salvaged from river bottoms. Right here in North Carolina, logs that have been submerged for more than 100 years are milled into truly unique flooring. Very often the reused and reclaimed wood flooring comes from trees that are no longer present to harvest, or in grain patterns only found in rare old large trees, enhancing the aesthetic quality of this type of flooring.

A little drop of water

Water conservation is another important factor when it comes to choosing green building materials. Choose Energy Star dishwashers and clothes washing machines. An Energy Star dishwasher uses about 40% less water than conventional models.  Front-loading clothes washers use less water (and also extract more water from clothes reducing energy demand for drying).

Low-flow showerheads use about 2.5 gallons of water per minute compared to between four and five gallons per minute used by conventional heads. And sink faucet aerators can cut the water usage of faucets by as much as 40% from four gallons per minute to 2.5. Low-flow toilets use a maximum of 1.6

gallons of water per flush compared with about 3.5 gallons of water used by a standard toilet. "That can translate to 2000 gallons of water a year!" says Stock Building supply's Nelson. "And these low-flow toilets have really come a long way in recent years in terms of flushing power." Hot water recirculating systems can be a green building material choice that not only saves water, but also homeowner frustration. Unlike standard hot water plumbing, where water that has been

sitting cooling in supply lines must first be flushed before hot water flows, a recirculating system incorporates a return line from the last tap on the hot water supply line. A small circulating pump keeps heated water circulating through the supply lines so that hot water flows immediately from the tap, saving hundreds of gallons of water over time, not to mention hours of time spent waiting for the shower to get hot.

We'll talk more in depth about the other facets of green building materials — energy efficient home products as well as how to choose products that maximize indoor air quality, in future issues. As with all of the aspects of green building, we have explored in this series, using green building materials is often a matter of forethought and planning. For almost every element of a new home today, there is an option that minimizes its impact on the global environment, by efficient use of natural resources, through technology and new manufacturing capabilities, through recycling and state-of-the-art engineering.

For more informtion, the NAHB Model Green Home Building Guidelines, are available free at www.nahbrc.org/green.

Kelly McCall Branson is a Freelance Writer