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Intimate Relationship Thermal performance issues are driving the development of new building envelope technologies and products by Godfrey Budd A n intimate relationship exists between the build- ing envelope and its thermal performance – and the resulting carbon footprint. As long as such issues as the cost of fuel and the need to control greenhouse gas emissions remain on the radar, a sig- nificant quorum of the design community will focus on improving the energy efficiency of the envelope. It wasn't always that way. "Only in the last 25 years has much attention been paid to the envelope," says Jason Taylor, senior project manager for special proj- ects at Skyline Building Envelope Solutions Inc. Indeed, although jurisdictions in North America and around the world are prodding the construction sector to make buildings more energy efficient, a busi- ness model in which developers often sell a building soon after it is built doesn't help. It divorces developers, or the original owners of a building, from operational concerns like the thermal performance of its envelope. But legislation and tougher building codes on the energy front, as well as the demands of those eventual owners who will have to deal with the operational issues, are increasingly favouring quality and energy efficiency. Owner-operators want good thermal performance, low maintenance and durability, not just a pretty face on the envelope – although that is often still welcome. It is no surprise then, that a lot of technological smarts these days is being invested in the envelope. Product quality almost across the board tends to be better. For instance, "No one makes a bad a vapour bar- rier. The key, now, is the workmanship of the installer," Taylor says. One of the newest vapour barriers is a product from 3M that is self-adhesive. It doesn't require a primer, is transparent and has recently been used on some large projects in Western Canada. The design of today's envelope systems can make repairs ranging from a minor adjustment to an insula- tion retrofit easier than it was in the past, Taylor says. "Most wall systems are insulated from the exterior. Once the cladding is removed, you can check the insu- lation and then, if necessary, replace the cladding and insulation. Also, most insulation in commercial build- ings is mineral fibre and non-combustible and doesn't absorb moisture." He adds that a lot of development work has been done so that components and new products for the envelope won't propagate a fire. The popularity of rainscreen systems has spurred innovations for drainage in the envelope cavity that replace traditional strapping strips. The WaterWay Rainscreen Drainage Mats from Stuc-O-Flex Interna- tional, Inc. consist of a polypropylene core of fused, entangled filaments in a range of thicknesses from a nominal one-quarter inch to three quarters of an inch, depending on cavity space dimensions and cladding selection. The drainage mat core is bonded to a white filter fabric, which is moisture-resistant but allows air to flow through. This recent innovation is designed to function as an additional weather barrier. "The white fabric is a new addition to the product. No one else has this type of system that has both water resistance and air permeability," says Dan Johnson, technical sales manager at Stuc-O-Flex. "Research sponsored by the New Zealand government found that air in this context typically only moves up and down. Our product allows the air to move in all directions." The WaterWay Rainscreen Drainage Mat line has been on the market for 15 years with 40-million square feet sold. The filter fabric addition is made from spunbond polyester, a non-woven material with some useful qualities – strong, lightweight, stable at temper- atures up to 150 degrees Celsius, chemical and water resistant. "Spunbond polyester of this type is a very new technology," Johnson says. He adds that one of the benefits of the fabric is that it obviates the need for any extra house wrap outside the furring strips. Insulation is another envelope sector where the product plethora seems capable of many iterations and refinements. Some new spray foam innovations from Icynene Inc. that were announced in April this year are a case in point. The new product from the spray foam manufacturer is a 0.7-pound-per-cubic-foot open-cell insulation that achieves a high R-value in typical two- by-six wall assemblies. "Icynene Classic Plus provides R22 in a 5.5-inch- deep cavity and meets all prescriptive R-value require- ments in all regions," says Paul Duffy, VP engineering at the Mississauga-based company. Icynene Classic Plus is designed as a lower cost means of meeting insulation needs. "When using it, Photo: Regata Condominiums, Seattle, WA. Retrofit project using WaterWay Rainscreen, Stucco & Stuc-O-Flex Finish. Photo courtesy Stuc-O Flex International. Building Envelope 14/ AUGUST 2014