ISSUE 4/2009 V O L U M E 2 6 N U M B E R 4 Journal of architectural technology published by Hoffmann Architects, Inc., specialists in the rehabilitation of building exteriors. The Building Envelope: Energy Efficiency and Economics Richard P. Kadlubowski, AIA and Dean W. Yates, AIA According to the U.S. Environmen- As these structures age, we are tal Protection Agency (EPA), the con- faced with a choice: rehabilitate and struction and operation of buildings is upgrade the inefficient buildings, or responsible for nearly half of America’s replace them. greenhouse gas emissions. In com- With landmark and historic struc- parison, all forms of transportation tures, the importance of preserving combined—including airplanes, trucks, the existing building is clear. But what buses, and cars—account for just a about buildings that are neither ef- quarter of total emissions. Because so ficient nor architecturally significant? much of the country’s building stock Replacing an old building with a new was constructed when fuel was cheap one uses energy. That energy takes and plentiful, little regard was paid to many, many years to recover through designing energy-saving enclosures. improved performance—if at all. A better approach, then, is to improve the energy profile of the buildings we already have. To cut back on energy consumption, federal, state, and local authorities have adopted increasingly rigorous standards for building performance. These regulations, along with tax incentives for improved energy man- agement, have led to an upsurge in energy efficiency retrofits for existing structures. Before investing in major capital improvements to heating and cooling systems, however, consider making simple, less costly upgrades to the building enclosure. A sound exterior envelope acts as a thermal shield, reducing demand on HVAC As the barrier between the indoor and outdoor environments, the building envelope is critical equipment, improving indoor comfort, to energy performance. and extending the lifespan of building components. Richard P. Kadlubowski, AIA, vice president and senior architect, and Dean W. Yates, AIA, project architect, manage projects at Hoffmann Architects’ Washington DC office. They develop energy-saving strategies for the building envelope that are sensitive to system interdependence, performance objectives, and cost-effectiveness. JOURNAL Roofs HEAT CONDUCTED THROUGH WET INSULATION More often than not, faulty roofs are behind performance-compromising conditions, from leaks to heat loss. As WARM AIR EXFILTRATION the portion of the building hit hardest AT OPEN by acid rain, UV light, snow, ice, foot JOINTS AND traffic, and chemical pollutants, the GAPS IN roof tends to degrade faster than do INSULATION other portions of the building exterior. Leaks Are More than Dripping Water They’re also a source of heat loss. Wet roofing materials lose their insulating properties, causing the roof to act as a conductor, rather than an COLD insulator. Heat rises, so without a OUTSIDE thermal barrier at the roof level, heat AIR travels up and out of the building. Limit potential points of water entry by minimizing the number of pen- HEAT LOSS etrations through the waterproofing THROUGH POOR WINDOW SEALS membrane. Don’t neglect flashing details; the roof perimeter, along with any intersections between the roof membrane and parapet walls, pent- WARM RADIATION houses, or other roof levels, is an easy target for moisture if not correctly INSIDE AIR THROUGH WINDOWS sealed and protected by the flashings. Is Your Insulation Really Insulating? Insulation secured with fasteners may not have you covered as well as you thought. For steel decks, the metal acts as a thermal bridge, conducting HEAT LOSS heat through the insulation. A safe- THROUGH guard would be a multi-layer system, COLD AIR WET with chemically adhered insulation INFILTRATION INSULATION over mechanically fastened boards. Even with fully adhered insulation, if sections are not fully abutted, it is pos- sible for air to pass through the gaps between boards. Staggered joints cover any space between sections. Not Every System Is Right for Every Building Cool roofs, green roofs, solar roofs… Heat Loss In Winter overwhelmed with all the options? You’re not alone. But the kind of 2 V O L U M E 2 6 N U M B E R 4 A design professional can assess your Cool roofs reflect heat, cutting energy costs and normalizing urban temperatures. Pictured roof’s insulating properties. here is a modified bitumen roof (MBR) with a reflective capsheet. building you have—as well as the roof absorbing concrete and asphalt, cool Facades that’s already in place—might make roofs help to cut down on mass heat A facility manager replaces outdated choosing an energy-efficient roofing retention known as the “heat island cooling equipment to improve energy system easier than you thought. effect.” When selecting a product, performance, then adds a solar film Green roofs, also known as vegetated consider material shortcomings, such to the windows as an inexpensive ef- roofs or verdant roofs, incorporate as potential for split seams or non-uni- ficiency upgrade. Smart thinking, right? plants into the roof assembly. They form coverage; for some systems, the Well, almost. These are both good add insulating value, reduce storm risk of premature failure may outweigh ideas—just in the wrong order. the benefit of increased reflectance. water runoff, cool the building interior The facility manager bought the chiller and the surrounding area, provide Solar roofs use photovoltaic cells to system to accommodate existing cool- habitat for birds and insects, and look convert sunlight into usable energy. ing demands, and then reduced those great. But they can also be heavy. Solar panels are not a roofing material, demands by adding the window coat- While this might be an excellent however; like any rooftop equipment, ing. Not only did the facility manager sustainable retrofit for some buildings, they can cause leaks if installed incor- overspend, the now-outsized chiller it could be structurally disastrous for rectly. Unless your roof is in good wastes energy, costs more to operate, others. Before you commit, a design shape, the expense of repairing water and decreases indoor comfort. professional should evaluate the load- damage could cancel out any cost sav- bearing capacity of the building and The lesson: before making big-ticket ings from the solar power. determine if structural modifications improvements to mechanical systems, would be necessary to support plant- The Energy Star program, created by ensure that your facade provides a ings, growing and drainage media, and the U.S. Environmental Protection good thermal barrier. related components. Agency and the U.S. Department of Seal It Up… Cool roofs sound appealing. But what Energy, can help you and your de- Cracked, loose, or missing mortar is a cool roof, anyway? In its simplest signer evaluate the options, with tools joints and deteriorated sealant joints form, a cool roof is just a roof that’s to measure performance, compare allow moisture to enter the wall. Be- light-colored. So what’s the hype? products, and track savings. All of the cause water conducts heat, wet walls Darker colors absorb heat. A white above systems can earn Leadership lose their insulating value and make or reflective roof can cut cooling costs in Energy and Environmental Design mechanical equipment work harder to by reflecting heat away from the (LEED) points for a retrofit project. keep up with heat transfer. The same building. In urban areas, where there The important thing is finding which holds true for glass curtain walls and one is right for your building. is little greenery and lots of heat- windows, where deteriorated gaskets 3 JOURNAL Problem areas to watch for: Solar films or tints keep rooms • Broken gaskets and seals. Without cooler in bright sunlight and cut down a proper seal, windows permit on glare. Shaded glass that responds water and air to pass through at the to an applied electrical current offers perimeter. Condensation between variable opacity control. panes usually points to a broken Thermal breaks, which are plastic or thermal seal, which means that the rubber separator materials, minimize insulating capacity of the window heat conduction across inner and has been compromised. outer window frames. Repair cracks, but leave weep holes open, • Failed thermal breaks. Cold / hot Technologies are constantly evolving. so water can make a quick exit. spots or condensation on window Work with your design professional to frames could point to damaged or assess your energy goals and building and seals not only let in water, they missing insulator material. condition to maximize window ef- create drafts and temperature fluctua- • Glare. Daylighting is important ficiency and minimize costs. tions at the building periphery. to minimizing energy consump- tion, but when it comes to sunlight, ...But Let It Out more isn’t necessarily better. Glare Not all holes in the building exterior diminishes visibility, particularly at are bad. Often, well-meaning mainte- computer workstations. nance personnel make the mistake of • Solar heat gain. Direct sunlight can sealing over weep holes, small voids in also cause overheating. Designers exterior walls that drain water from use the solar heat gain coefficient within the wall cavity. When dry, these (SHGC), a measure of transmitted cavities provide insulating value. But if solar energy, to optimize windows’ water becomes trapped, the thermal impact on indoor temperature. conductivity of the wall increases and Failed sealant provides a pathway for heat, air, and moisture transfer. heat escapes. The constant presence • Drafts. Heat fluctuations not only of moisture also leads to other prob- mean that HVAC systems have to work harder to stabilize tempera- lems, from mold growth to building ture, the variable conditions can Are Your Doors Leaving You Wide component degradation. make the building periphery uncom- Open? fortable. In terms of square footage, windows Strategies for improving window outrank doors as the facade element performance range from taking aim most critical to energy conservation.