Not every environmental benefit of a design/construction product or practice fits neatly into the categories of various green building rating systems. For example, the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design® (LEED®) framework reserves up to four credits under a broad category, Innovation and Design Process (ID) Credit 1, Innovation in Design
. Once again, various plastics products can provide solutions to potentially achieve special recognition.
Extruded polystyrene (XPS) used in the construction of protected membrane (PMR) garden roofs and/or PMR assemblies designed to temporarily store stormwater can generate a positive environmental impact. XPS fits well into garden roof design due to high compressive strength, high moisture-resistance, and stable R-value in the presence of moisture.1 Extruded polystyrene insulation is used in insulating concrete forms (ICF), which are panel systems with composite ties. Walls made with these ICFs are extremely energy-efficient, combining both thermal insulation and thermal mass while also providing structural capability and interior/exterior standalone finishes. Walls constructed with insulating concrete forms may be reusable, and the concrete could contain significant amounts of recycled material.
When the National Association of Home Builders (NAHB) developed its Model Green Home Building Guidelines, it took into consideration the low-maintenance characteristics of green building materials. The guidelines award credits for materials that do not require “priming, painting, and/or additional resources at the installation stage and save on resources for recurring maintenance.” Vinyl siding continues to be one of the most popular cladding materials in the United States, due in part to its low preservation needs.2 The material does not require painting; rather, it is simply washed from time to time to eliminate dirt and dust.
Vinyl siding’s color palette, texture, and design continue to expand, making it a viable alternative in restoration projects. For example, polystyrene-backed vinyl siding provides a thickness some have used to give the authentic look of old clapboard on older homes.
Vinyl’s durability and low maintenance have also made it a popular material for fencing and decking. There are no fibers in the product, so burrs, splinters, chips, or slivers are eliminated. Due to added stabilizers and ultraviolet (UV) inhibitors, the products are weather-resistant and waterproof. Vinyl does not blister, rot, rust, or peel and weathers uniformly. As such, it is unlikely to need paint or other surface treatments such as water sealants and stains. Similarly, testing for chemical resistance reveals the material is unaffected by rock salt or other chemicals used for snow removal.
High-density polyethylene (HDPE) pipes can be bent to a radius 25 times the nominal diameter (e.g. 305-mm [12-in.] HDPE pipes can be cold-formed in the field to a 7.6-m [25-ft] radius). This can eliminate many fittings required for directional changes in a piping system, where fittings and thrust blocks or restraints are required with alternate materials—thereby reducing material use.
Other potential environmental concerns, such as infiltration and exfiltration experienced with alternate pipe joints,3 can be minimized with HDPE pipes. Advantages to the HDPE smoothwall pipe-joining system include the ability for on-site fusing and the fact the joints can become as strong (or stronger) than the pipe itself and therefore leaks are virtually eliminated. This helps contribute to the longer life-cycle cost of HDPE pipe, since its allowable water leakage is nearly zero, compared with typical leakage rates of 10 to 20 percent for other types of pipe.
This combination of flexibility and leak-free joints allows HDPE pipes to be installed in unique and cost-effective ways that are not possible with rigid alternative pipes that rely upon bell and spigot connections. These innovative installation methods (e.g. horizontal directional drilling, pipe bursting, sliplining, plow and plant, submerged or floating pipe) can save considerable time and money in most potable-water applications.
Cross-linked polyethylene (PEX) pipe features a three-dimensional molecular bond created within the structure of the plastic. Through chemical/physical reactions, manufacturers structurally modify the polyethylene chains, significantly improving performance on properties such as high-temperature strength, and chemical, abrasion, and stress-crack resistance. The resulting flexible pipe has greater impact and tensile strength, improved creep resistance, and performs extremely well at high temperatures and pressures.
The success of the various green-building programs, and the rising public awareness of the relationship between the built environment and the natural one, are signs the philosophy of sustainable design is a paradigm shift, rather than merely a fad. Design professionals educated in the energy-efficiency characteristics of various plastics can ensure the products they specify fit within the framework of rating systems such as LEED, and can assist in the earning of points and credits.
1 As insulation formulation can vary from manufacturer to manufacturer, design professionals should consult the suppliers’ specification sheets to understand the exact properties, including the actual R-values. Factors affecting the R-value include thickness of application (i.e. the thicker the foam, the better the aged R-value), the substrate, and the covering systems used (i.e. the lower the perm-rated covering and substrate, the higher the aged R-value).
2 See “Vinyl Siding Comes of Age—Renewing aging buildings,” by Anita Blumenthal in the May 2005 issue of Modern Materials.
3 See “HDPE Solutions for Water Infrastructure Rehabilitation,” by Camille George Rubeiz, PE, in the May 2005 issue of Modern Materials.