Walls & Ceilings Architect/October 2007

reduce air leakage. Specify interior air barriers to reduce the potential for convective loops and increase drying capability. Always incorporate water resistive barriers and provide ventilation and drainage space behind the masonry façade to reduce wet ting the substrate materials and to promote drying. This exterior wall configuration is a cost-effective way to achieve thermal performance while managing moisture. Metal Buildings Metal buildings have their own set of installation and compliance recommendations. An authoritative publication covering ASHRAE 90.1 is available from the North American Insulation Manufacturers Association. It’s available online at www.naima.org. NAIMA’S reference for ﬂ exible ﬁberglass insulation used in metal buildings, Standard 202-96, provides information on thermal performance of metal building roof systems and wall systems. R-value and U-value data are listed for screw-down roofs and for sidewalls having varying cavity Rvalues and fastener spacing. Fenestration Fenestration refers to any opening in a building envelope, including windows, doors, curtain walls and skylights. The National Fenestration Rating Council (NFRC) offers a labeling and certiﬁcation program for window and door products. Factors that affect window performance include frame type, glazing type, type of gas ﬁ ll—argon vs. air, for example—and low-emittance coatings. When installing high-performance windows, one should look for the NFRC label. Here’s what to look for: U-factor in windows is similar to R-value in insulation products; both are indicators of thermal performance. Energy Star U-factor recommendations are given by zone. With U-factor ratings, the lower the number, the greater the thermal resistance. This is just the opposite of R-values, in which the higher number is better. Another indicator to look for is Solar Heat Gain Coefﬁ cient (SHGC). This number- rating indicates a window’s efficiency in preventing solar radiation from entering and heating a building and from escaping the building in cold weather. Since windows are generally made from thermally conductive steel or aluminum, it’s important to select thermally broken windows with an air space between components. A lower U-factor not only means increased energy efﬁciency, it means better condensation control on surfaces. Installing airtight systems will increase energy efﬁciency and reduce the potential for moisture accumulation. Hidden mounting ﬂ anges and metal surfaces need to be insulated to reduce surface condensation. The goal should be to have an airtight, moisture-resistant installation. SEALING IT ALL UP With the current embracing of the sustainable building design movement, the number of energy-saving, healthy, long-lasting buildings is bound to increase in the years to come, through both new construction and retro-ﬁtting. Following these thermal control design guidelines should offer a good start toward achieving this goal. W&C Stan Gatland is Manager of Building Science Technology, CertainTeed Corporation. October 2007 | Walls & Ceilings Architect | 29 http://www.naima.org

Table of Contents Feed for the Digital Edition of Walls & Ceilings Architect/October 2007

Contents Trade News Silver Certiﬁed Airtight The Men of Steel Thinking Thermal Firestop 101 ICFs Create a Tight Envelope The Finish Line The Green Thumb Cracking the Code

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