Balancing Performance & Sustainability
When the word “plastic” enters design conversations, PVC (polyvinyl chloride) piping, siding, window frames—maybe even roofing—come to mind. Few consider insulation, moulding trim, wallcoverings, bathroom fixtures, flooring, beams, columns, and doors as derived from plastic, let alone the plastics blended into products for concrete chemicals, wood board, and paint. While this list of products clearly demonstrates plastics are prominent in today’s building market, many have yet to recognize the material as an answer for sustainable and green building design.
A recent survey of building professionals conducted by NFO World Group for the American Plastics Council (APC), indicates the most important characteristics considered in the selection of a building material are: safety (65 percent), durability (60 percent), and contributing to a healthy environment (59 percent). Unfortunately, the respondents failed to recognize plastics as a strong performer in those areas: only 23 percent listed plastics as easy to maintain, 22 percent rated them high in durability and versatility, and a mere 17 percent recognized plastics as a safe material. This contradiction between perception and reality hinders the adoption of plastics and the realization of their contribution to sustainable design.
As polymers, plastics are made up of chains of many different molecules, such as carbon, hydrogen, oxygen, and/or silicon. The majority of polymers are thermoplastic, meaning they can be formed, heated, and re- formed repeatedly. This property permits easy processing and facilitates recycling.
The construction industry accounts for the single largest end-user of polyurethanes (almost 635,029 t [700,000 tons] per year) in the form of rigid foams, binders, coatings, sealants, and adhesives. Accounting for more than 57 percent of polyurethanes used in construction, rigid foams are used in roofing and wall insulation, foam core panels, insulated doors, and air barrier sealants.
Due to their flexibility and versatility, they can be cut into sheets, slabs, or any desired design, as well as sprayed in place to meet specific building code requirements or custom designs. Polyurethanes are a durable sustainable design solution because they often arrive at the job site as a liquid, which saves on transportation costs and reduces waste.
Polyurethane-based binders, used both with wood and rubber, account for the second largest end-use of plastics. They are used in composite panel products to permanently join strands into oriented strandboard (OSB), hardboard (HB), medium-density fiberboard (MDF) and strawboard, particleboard (PB), and laminated veneer lumber (LVL).
Polyurethane-based sealants are used in joints and openings to prevent the passage of gases, liquids, and solids (dust and dirt). Similarly, polyurethane-based adhesives are used to bond wall and ceiling panels to the structural frame, floor joists to the sub-floor decking, and structural end, side, and interior shear walls to gypsum wallboard.
Polyurethane elastomers are used in the manufacture of outdoor and indoor athletic surfaces, as well as insulating windows, creating a thermal break and barrier to prevent heat loss and condensation build-up on the interior of the frame.
Spray polyurethane foam (SPF), used as roofing and insulation system applications, conforms to the surface to which it is applied￼and forms a seamless layer of insulation. Since SPF fills in gaps and seams during application, it is increasingly being used as an air barrier. SPF exhibits a high degree of sustainable characteristics, owing primarily to the minimal energy used in manufacturing the lightweight plastic, as well as decreased energy and transportation costs.
Energy studies performed by Texas A&M on their own roofs (presented at Texas A&M SPF Roofing Experience by Sam Cohen, PE, 1994) show the energy cost reductions obtained by applying SPF to more than 743,224 m2 (8 million sf) of roofing paid for the cost of the retrofit in a little over three years. SPF adhesives offer exceptional wind up-lift resistance, exceeding 3447 kPa (500 psi) over some substrates.
Polyisocyanurate (polyiso) laminate boardstock, used primarily in roofing and wall insulation, accounts for 85 percent of the total usage of rigid polyurethane foam in construction applications. It offers high insulation value— ranging between 5.6 to 7.9 R-value per 25 mm (1 in.)—as well as good moisture, fire, and impact resistance.
Another area in which plastics are becoming more commonly specified is the growing use of expanded polystyrene (EPS) in insulated concrete forms (ICFs). In this application, EPS provides lower energy bills, decreases noise by as much as one-third compared to ordinary insulated frame walls, and increases ease of construction and design flexibility.
Selecting EPS as a sustainable building element is increasing with the variety of products now available, such as geofoam (used as lightweight fill, thermal insulation, compressible inclusion, drainage, noise and small- amplitude vibration damping, and structural and soil stabilization). Plastic geofoams have a density that is only one to two percent of the density of soil, yet can be designed to be sufficiently strong and stiff enough to support road, rail, and aircraft loading.
The use of polycarbonate windows offers designers another alternative. Boasting a lower thermal conductivity than glass, use of this product reduces heating and cooling energy needs while providing additional high- strength, shatter-resistance during dangerous storm or hurricane weather.
|Plastic Resin||Alternative Product and End-Use||Energy Savings in Trillion J (Btu)|
|Polyurethane||Rubber for carpet underlay||20,574||(19.5)|
|PVC||Ceramic tile or linoleum for flooring||14,982||(14.2)|
|HDPE or PVC||Metal for gutters and downspouts||1,477||(1.4)|
|Polystyrene or polyurethane||Fiberglass for insulation||42,835||(40.6)|
|Polystyrene or PVC||Metal or wood for lighting components||29,964||(28.4)|
|PVC, unsaturated polyester||Metal or wood for paneling and siding||27,009||(25.6)|
|ABS, HDPE, polystyrene, PVC unsaturated polyester||Metal, concrete, or vitrified clay for pipe, fittings, and conduit||348,696||(330.5)|
|Unsaturated polyester||Metal/porcelain for showers/tubs||5,064||(4.8)|
|PVC||Metal or wood for window units||2,005||(1.9)|
Still, the plastic most commonly used in building applications is vinyl, or PVC. This form of plastic can be forced through a mold to form long lengths of product, such as siding; injected into a three-dimensional mold to create electrical outlet boxes; put through a calendering process to produce film and sheet products for flooring or wallcovering; thermoformed for rigid uses such as shower trays; and dispersed in a solution and coated to make products like carpet backing, or vinyl-coated products like closet shelving.
Regardless of the end product, there is little that challenges vinyl’s versatility, durability, and possible textures, colors, and shapes. In the United States, two-thirds of all vinyl is used in building and construction applications, and while new applications continue to evolve, PVC continues to benefit the environment.
The vinyl resin manufacturing process is essentially closed, so nearly all waste is recycled. In fact, more than 99 percent of all vinyl manufactured ends up in a finished product. Another life-cycle assessment determined vinyl production accounts for a fraction of one percent of all U.S. oil and gas consumption. The same study compared the manufacturing processes for vinyl and metal-clad windows and determined vinyl used approximately three times less energy—equating to nearly 2110 trillion J (2 trillion Btu) of energy per year in the United States—which is enough to meet the yearly electrical needs of 18,000 single-family homes.
Beyond the manufacturing and transportation processes, many vinyl building products save energy for the end-user. For example, vinyl transfers heat more slowly than metal-clad window frames, so utility costs are kept low.
Single-ply vinyl roofs are also energy efficient. Research from the Environmental Protection Agency (EPA), the National Aeronautics and Space Administration (NASA), and the Federal Department of Energy (DoE) shows reflective roofs—plastic assemblies that bounce sunlight and radiant heat away from a building—lower a building’s air-conditioning costs by up to 40 percent (Green House, APC).
Mindsets are often difficult to alter—such as the notion of “natural” materials or products compared with “synthetic” materials or products. Mahogany is good material, but it is too expensive and takes too long to grow to be practical on a mass scale. However, synthetic or synthetically modified materials provide the durable and cost-effective solution not always possible with stand-alone natural products. As such, one sustainable design solution is to use plastic binders with wood chips from trees that grow rapidly.
Specifiers are facing increasing pressures to use/not use certain products. In a handful of states, proposed regulatory language and tax incentives have already been introduced to incorporate certain products based on “green” attributes. However, specifiers are cautioned to focus less on product and more on the sum of the products as a system.
Sustainable design goes far beyond simply creating products that benefit consumers with cleaner air, cost savings, and durability. Rather, effective sustainable design illustrates a full- systems approach of products in the environment, and their interaction with other products.
A systems approach determines the energy requirements of a product. This means determining energy consumed at each stage of a product’s life cycle, beginning at the point of extraction from the earth, through processing, manufacturing and fabrication, end-use, and disposal. End-use can account for as much as 90 percent of a product’s impact on the environment. Transportation of materials and products through each process step must also be calculated.
In terms of energy used during production, only about four percent of the United States’ energy consumption is actually used to produce plastic raw materials, including feedstock. Often, less energy is used to convert plastics from a raw material into a finished material than comparable products.
The most common misconception about plastics is they are cheap and flimsy. Today’s plastics comprise sophisticated compounds and are designed with sustainability in mind. They are easy to clean, last longer than many natural materials, and often leave a lighter environmental footprint.
Did You Know?
Foam plastic insulation controls unwanted air infiltration—in and out of the building— a problem wasting potentially close to 40 percent of every heating and cooling dollar. Closed-cell foam plastic insulation can be efficient in a wide variety of temperature and humidity conditions.
Vinyl window frames require three times less energy to manufacture than aluminum window frames, saving the United States around 21 trillion kJ (2 trillion Btu)—enough to meet the yearly electrical needs of 18,000 single-family homes.
About the Author
Mason Knowles is the executive director of the Spray Polyurethane Foam Alliance and former technical director of the American Plastics Council (APC). He is a member of ASTM International and chairs Subcommittee D08.06 on Spray Polyurethane Foam Roofing Systems. Knowles has written and/or co-authored more than 40 technical papers, and can be reached via e-mail at email@example.com.
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