Sustainable design features are often like a green badge of honor: We like them to be visible, like the solar panels, grassy rooftops and bike racks that decorate many green building projects.
But like a hybrid car, the true green – and the performance efficiencies that come with it – are often buried deep inside: Insulation and geothermal wells, for example. Or they are hidden in plain sight, like the colorful building-integrated photovoltaics from Onyx Solar, for example, or the see-through window insulation, In’Flector.
Let’s face it: Green is unseen.
When we look at two building wall systems, it’s impossible to tell which is the greenest. Yet the better building features a number of invisible advantages:
1. Energy savings. One thing that separates the LEED earner from the energy hog is the selection and detailing of wall assemblies. Air barriers are hidden from view, but one look at the property’s utility bills will show whether they are installed – properly. A report by NIST shows that continuous air-barrier systems reduce air leakage by up to 83 percent – and energy consumption by up to 40 percent.
“Infiltration in commercial buildings can have many negative consequences, including reduced thermal comfort, interference with the proper operation of mechanical ventilation systems, degraded indoor air quality, moisture damage of building envelope components and increased energy consumption,” said the report authors, led by Wagdy A.Y. Anis, FAIA, now with Wiss, Janney, Elstner Associates, Boston, and by Steven J. Emmerich of the Building and Fire Research Laboratory
2. Toxins. Wall components in green buildings contain little or no hazardous ingredients. But you can’t see VOCs, lead, mercury or PCBs anyway, so it’s hard to know when your building is really green or not.
For a shortcut, start with a cheat sheet listing materials and products that contain “worst-in-class chemicals,” says the advocacy group Healthy Building Network in Washington, D.C. These are persistent bioaccumulative toxins, or PBTs, which include chlorinated materials like PVC, brominated flame retardants, and all heavy metals.
3. True waterproofing. Moisture problems may be visible on some buildings as wetted materials, efflorescence on brick, rusty streaks, and even mold patches. But in many cases, envelopes with water problems may look no different than those that are truly watertight.
Yet green buildings are detailed to prevent unintended water ingress. According to the Building Science Corporation’s Dr. Joseph Lstiburek, “Rain is the single most important factor to control in order to construct a durable structure.” Effective management of liquid water depends on continuity of the water barrier and its connections to windows, louvers, curtain walls and even minor penetrations. Green walls have well-designed drainage planes, flashings, weeps, and weep baffles, and cleverly incorporate high-performance waterproofing.
4. Structural and durable. Moisture is only one step in the direction of durability. All the building products must be durable, especially those exposed to the elements.
Green buildings are made of products and materials that retain their green properties under the variable conditions of the jobsite and the building life. A structural air barrier, for example, made with a fluid spray-applied to a durable substrate, will last as long as the waterproofing, helping to equalize pressures and preventing rainwater penetration, as Anis writes in the Whole Building Design Guide.