High-performance windows and doors
Learning objectives After reading this article, you should be able to: Understand issues of thermal performance and energy efficiency in relation to window and door systems; describe optimal detailing of the window-wall interface and how it contributes to building performance, sustainability, and occupant well-being; understand how durability contributes to sustainable windows/doors; and list sustainable O&M requirements for window and door systems.
Entryways speak volumes about a building’s character and function. From the façade and the entry’s frame or arch to the door material and hardware, these access points can be grand and celebratory or modest and secure. In any event, they represent the first direct point of interaction with the public, so aesthetics and capabilities play a key role at these key building nodes. According to Building Design+Construction’s 2011 survey on window and door trends (http://www.bdcnetwork.com/article/how-aec-professionals-choose-windows-a...), energy implications and thermal performance came out on top of the most important factors considered by Building Teams in the choice of windows, with 87% of respondents ranking these factors as the most important for window systems, with durability and reliability of windows and window systems coming in second (at 73%), followed by weather resistance at 70%.
However, the difference between “durability” and “weather resistance” in this case is not statistically significant, given a margin of error of about 4%. In the case of doors and door systems, 76% of respondents listed energy factors and thermal performance as most important, with durability slightly behind at 75%. Again, however, given the margin of error (about 4%), these sets of factors could be viewed as in a virtual tie in terms of door selection criteria. For both windows and doors, respondents to the BD+C survey ranked these four factors as most important: energy/thermal performance, durability and reliability, weather resistance, and aesthetics—statistically more important than “code requirements” and “initial cost (including installation)” in choosing both windows and doors, according to respondents.
Sustainability also factors into the equation, particularly with regard to the integrity of the building envelope in terms of thermal performance and the impact on overall energy usage. Thus, Building Teams cast a broad net in assessing the sustainability of window frames and door materials. Dean Vlahos, FAIA, CCCA, LEED AP, a forensic architect and principal with DLR Group WWCOT (www.dlrgroup.com), Santa Monica, Calif., considers the “residual value” of each material and the energy usage, in terms of manufacturing and performance, as part of a thorough life cycle analysis. Others note that accurate measurements of embodied energy are difficult to calculate.
Mark Schmidt, CSI, LEED AP, a specifications writer and project coordinator with Fanning/Howey, Celina, Ohio, states that theoretically the computation could only be done if you had access to the first costs and operating costs of all of the materials in the wall openings market—a practical impossibility. Therefore, the study of embodied energy is far from an exact science, but it can be applied in a qualitative and relative manner, although not as the main determinant for choosing a sustainable product. Instead,
“Sustainability means longevity and endurance. Sometimes life cycle can completely offset initial embodied energy,” says Adam Zimmerman, AIA, LEED AP, principal of Zimmerman Workshop, Brooklyn, N.Y. The definition of durability is substantially less subjective, notes Duo Dickinson, AIA, NCARB, principal of the eponymous Madison, Conn.-based firm known for civic projects and housing. Dickinson prioritizes “long-term survival” for window and door designs.
For example, he favors windows that do not need to be painted. However one defines sustainability, it is still difficult to compare window and door offerings that purport to meet the objectives of green Building Teams. Sustainable options run the gamut from recycled aluminum frames—energy intensive in terms of manufacturing, but lightweight, highly resilient, easy to install, and low maintenance—to steel, which is robust but heavier than aluminum and in some instances more susceptible to the elements.
Specifying aluminum or steel can help a building add to its percentage of recycled content and potentially earn one to two points toward U.S. Green Building Council LEED certification, though the additional weight and maintenance for steel have made it less common, according to Stephen William Buck, AIA, CSI, CDT, principal, RTKL Associates, Washington, D.C.
Certified wood is another option, but it is not always available in most wood product designs from most manufacturers.
IN SEARCH OF THERMAL INTEGRITY
While embodied energy, recyclability, and stewardship of timber sources remain contentious topics, there is little argument that thermal performance is essential in the design of openings for new and renovated buildings.
“A key design feature is having a thermal break in a metal window system. I know of very few products today that don’t have this attribute. It is nearly always specified,” says RTKL’s Buck, who has been working with window and door specifications for more than three decades.
According to U.S. Department of Energy (DOE) Building Energy Codes Resource Center, the thermal break is the most common solution to heat-conduction problems in all exterior systems but especially for high conductors like aluminum and steel. The window or door frame design is split into multiple components—typically separate pieces that are interior and exterior relative to the enclosure—with a less conductive material used to join the sections. Current technology with standard thermal breaks has decreased aluminum frame U-factors (a measure of heat-loss rate) from roughly 2.0 to about 1.0 Btu/(hr-sf-°F).
Because the primary heat losses or gains from window or doorframes occur via air infiltration and thermal conduction, thermal breaks protect against direct thermal transmission. A recent change in the way thermal breaks are created in aluminum windows has improved overall envelope performance and frame integrity. According to Fanning/Howey’s Schmidt, until recently, thermal breaks in aluminum windows were provided using the ‘pour and de-bridge’ method. In that process, a structural polyurethane resin was poured into a void in the aluminum profile, and then after the resin had cured, a portion of the aluminum web underneath it was cut out leaving only the structural polyurethane to hold the now divided aluminum profiles together. In the new process, manufacturers separate interior and exterior aluminum profiles that are joined together with a pair of I-shaped polyamide extrusions that provide greater strength, increased insulating value, and a thermal coefficient of expansion closer to that of aluminum, thereby diminishing the potential for cracking and structural failure.
With improving technical solutions, Building Teams can expect better envelope performance.
“It’s that critical place where there’s more material that acts as a big washer and stops the thermal transfer,” says Philip Macey, AIA, division manager with Haselden Construction, Centennial, Colo.
When possible, wood frames offer a natural solution to thermal transfer problems, says Ira Smith, a principal with Smith Maran Architecture & Interiors (www.smithmaran.com), Montclair, N.J. In some cases, Smith recommends solid wood jambs because they offer added insulation. Novel wood frame designs that incorporate rigid foam as a thermal barrier for enhanced energy performance are also available from a number of European and U.S. manufacturers, according to Nils Petermann, program manager with the Efficient Windows Collaborative, a division of the Alliance to Save Energy (www.ase.org; www.efficientwindows.org), Washington, D.C.
When it comes to metal-clad wood windows, Smith, who chairs a local historic preservation committee and teaches architectural design at several universities, recommends jamb designs featuring an air space that helps create a thermal break in the window or door opening. There are also advanced framing designs that incorporate multiple chambers, according to the ASE’s Petermann: “With vinyl, fiberglass, and composite frames, improved insulating performance is often achieved through multi-chamber design incorporating several insulating air spaces or through foam insulation within the cavities.”
The Lawrence Berkeley National Laboratory software tool THERM is a useful tool to evaluate the thermal efficiency of different framing designs.
GET THE PERIMETER DETAILS RIGHT
While better insulation values are helpful, sealing the perimeter around window and door frames in the window-wall interface remains the weak leak in the thermal performance chain. Generally speaking, architectural specifiers prefer systems that provide a continuous membrane around the entire wall-to-frame connection. These jamb assemblies can reduce air leakage and moisture intrusion, provided they are properly detailed, correctly installed, and rigorously tested with field mockups. The barrier membrane wrapped fully around the perimeter protects the rough opening against water penetration, with flashing and other details directing any water toward the exterior, at or above the sill pan flashing. In addition to thermal breaks in the systems, a window insert should be used to optimize the performance of the sealant. Fanning/Howey’s Schmidt only specifies air barriers from manufacturers who offer full air-barrier systems, including transition details and materials.
“This makes one party responsible for the success or failure of the air barrier system—that is, apart from the door or window itself,” says Schmidt.
RTKL’s Buck favors peel-and-stick membranes for some projects to ensure a continuous waterproof surface, in addition to premolded corners, where possible, and stainless steel flashing. Unlike lead, copper, and copper composite flashing, Buck points out that stainless steel doesn’t stain the substrates and is compatible with virtually all sealants. Building enclosure experts note the continuous air barrier connection not only reduces leaking and condensation related to air movement, but also improves the acoustics and overall energy performance of the wall assemblies. When installing full air-barrier systems, Schmidt advises designing the head, jamb, and sill details in such a way as to not penetrate the flashing or air barrier when anchoring the window with fasteners.
“Depending on the location of the window in the wall depth, that might mean that some typical anchoring methods—for example, receptor systems and subsills—cannot be used,” he says.
Dickinson says he has found that full flashing with either an impregnated felt, a “weather-shield”-type product, or sheet metal (depending on the conditions) is what he calls “the first maximum effort.” He further recommends providing trim that allows for an extra layer of protection for all butt joints around a window or door and the cladding or siding. DLR Group WWCOT’s Vlahos stresses the importance of carefully following manufacturer guidelines.
“Their installation information is invaluable during the construction administration phase of the project as it defines the required location of diverters and sealant as tested and certified by the manufacturer,” he notes.
Another sometimes overlooked point is to ensure field measurements are double-checked to verify window opening sizes prior to system fabrication and delivery. If components have to be re-fabricated or alterations need to be made to the substrate or design, the project schedule can be severely impacted. Vlahos and other seasoned building professionals recommend choosing fenestration systems in which all components are provided by a single manufacturer.
Even so, Building Teams must be prepared for imperfections in the field. Vlahos points out that even though most aluminum window systems will provide factory pan flashings as part of their assembly, there can still be problems during installation.
“The factory pans do not always provide the proper seal at end-dam and back-dam locations, and typically do not recognize the minimum height as required by ASTM E2112-07. The result is water intrusion into the concealed area of a wall cavity, requiring costly repairs,” he cautions.
Similarly, whenever sheet metal pan flashings are identified on the construction documents, Vlahos states the method in which the end dam and back dam are sealed at the rear corner intersection must be identified.
“Too often, a thin layer of sealant is applied at the intersection, which will not perform as intended by the building code or designer,” he says. “The construction documents should clearly identify the intersection to be soldered and the corner of each pan flashing to be water tested prior to actual installation.”
TOWARD MORE DURABLE DOORS
Today’s Building Teams are fortunate to have a variety of door types and materials to choose from. According to the BD+C survey, 72% of respondents ranked aesthetics as the top driver for door selection, while 67% voted for performance, 54% favored initial cost, and 42% cited acoustical performance. Preferred door types included wood (72%), steel (58%), aluminum (39%), and glass (38%). “There’s nothing like a solid core—usually wood, but sometimes fiberglass—to make a door an acoustically effective barrier,” says SmithMaran’s Ira Smith. In addition to acoustics, solid-core wood products are known to fare well in terms of durability.
However, Zimmerman points out that wood exterior doors require maintenance over time. Similarly, fiberglass and PVC claddings may crack and delaminate under certain conditions, another reason that Zimmerman has recommended aluminum-clad solid core doors for a variety of projects.
“A simple solid-core door on the interior works quite well against sound transmission, and gives the feel and reality of durability and weight in operation,” he says.
Striking a balance between economy and durability on his projects, Fanning/Howey’s Schmidt prefers aluminum doors clad with fiberglass-reinforced polyester panels, with urethane foam cores. Meanwhile, RTKL frequently specifies painted, galvanized steel doors for their durability and ease of maintenance, although corrosion can be an issue depending on conditions of use. Still, Vlahos also ranks metal doors and frames as the best choice for highly trafficked areas. In cases where noise control is a primary concern, Vlahos points out that engineered insulated metal doors can achieve sound ratings of STC 57+/-, and wood doors offer STC 45+/-.
“Metal doors with wood veneers are also available for application in areas more sensitive to aesthetic considerations,” he adds.
Specialty door products, such as revolving and automatic sliding doors, offer convenience in both building design and operations. However, they are more expensive than conventional doors and their energy efficiency can be compromised by incorrect installation or operation, or by user abuse. As a result, they are generally reserved for specific and valuable applications, such as serving the requirements for handicap accessibility and Americans with Disabilities Act (ADA) requirements.
“Revolving doors are great in extreme climates where the indoor temperature varies significantly from the exterior temperature in heavy traffic zones,” says Zimmerman.
Sliding doors work well in moderate climate zones because they are easy to operate and quick to enter or exit, he notes. Zimmerman cautions that automatic sliding doors can allow undue amounts of conditioned air to escape, and vestibule designs are rarely large enough to prevent both sets of doors from opening at once. A compromise, says RTKL’s Buck, is to engineer door pairs used in sequence to create a suitable air lock.
“This configuration is less expensive than a revolving door and requires less maintenance,” he says.
As for aesthetic considerations, specialty doors are available in a growing range of finish materials and with treated glazings. The possibilities seem endless, with a full palette of painted colors, clear sealants to preserve natural wood hues and metal surfaces, as well as decorative glazings, including colored and fritted glass and applied films. For the most visible doorways and entrances, high-end finishes include stone, stainless steel, bronze clad, cast bronze, and metallic polyvinylidene fluoride (PVDF), a high-strength fluoropolymer-related plastic.
For vinyl assemblies, some manufacturers are beginning to apply heat-reflective coatings to doors, windows, and frames in an attempt to improve energy performance, notes Vlahos. As for door hardware, building designs tend to edge toward either discrete, modest applications or more elaborate, sculptural treatments—what some Building Teams call “door jewelry.” If the approach is toward jewelry look, “we prefer to let the real material shine with classic finishes such as oiled bronze,” says Zimmerman. ADVANCES IN
With newer technologies and design offerings for window and door handles, closers, operators, and locks, accessibility requirements and ergonomic trends are driving handle designs. Lever handles are a common choice at the moment for both exterior and interior doors. Available in polished brass, bronze, nickel, and steel, lever-type handles and their interchangeability of door handing has simplified the specification of certain types of hardware, says Vlahos. Similarly, locking products are easier to use even as they become more sophisticated. Many of the newer locks incorporate a reset function for quick re-keying of the lock.
In addition, a simplified design of many cylinder components enables less labor-intensive repairs and replacement work. At the same time, says Dickinson, “Locks are beginning to incorporate digital characteristics that often use Internet connections for locking and unlocking.” The industry is moving toward greater emphasis on multi-point locks, operable with a single lever.
“In some cases, the locking seems to serve double-duty, also improving the weather-tight seal,” says Smith.
Fasteners and latching devices for windows and doors can more easily be adjusted, as can door sweep speeds. Consequently, facility managers can optimize the time it takes for doors with automatic closers to remain open for entry and how quickly door leafs or panels close to discourage unauthorized entry. Closers should meet ANSI/BHMA standards for closing force and the portion of the door swing in which the door is controlled by the closer. As for the current generation of door operators, many are programmable with wireless radio-frequency transmitters, which makes their operation fully automated but also customized, says Vlahos, in contrast to mechanically controlled, relay-based systems. The high-tech features are making access control products more appealing. Fanning/Howey’s Schmidt says his firm specifies rim-type exit/panic devices equipped with optional electronic latching and linked to an adjacent proximity reader and/or to a central control station.
“This arrangement is particularly amenable to existing conditions where the previous solution was to cut out a portion of the existing door frame to accept an electric strike – which then frequently overheated due to overuse,” he notes.
With life safety egress locks and releases also tied into the security system, operators are afforded a much higher degree of monitoring and control. Another point to keep in mind when specifying door hardware is to make sure the product type is an appropriate match in terms of load capacity, cycle frequency, and size. For example, doors for a 24-hour train station or supermarket will require door hardware that is very different from that for a door to a file storage room, says Buck.
As a rule of thumb, Buck states that doors larger than the standard 3 feet by 7 feet require heavy-duty hardware. In addition, shielding—including acoustic or radiation—cladding materials for finishes or weatherability, or inset materials such as ornamental glazing, require higher-duty hardware. In terms of matching access control with the door type, Vlahos explains the security lock type must be coordinated with the size of the frame receiving the device. “In addition, power considerations for the operation of the locking devices must be coordinated with the actual power source,” he says. To assist specifiers, Vlahos points to the standard ANSI/SDI A250.8-2003 (R2008), which recently replaced SDI-100, Recommended Specifications for Standard Steel Doors and Frames. In addition, he cites ANSI/SDI A250.4- 2001, Test Procedure and Acceptance Criteria for Physical Endurance for Steel Doors, Frames, Frame Anchors and Hardware Reinforcing as a valuable resource.
UPGRADING MAINTENANCE AND OPERATIONS
When hardware is appropriately selected for a given application, better performance and longevity are the result. Conversely, when hardware is improperly specified for the expected service duty, it will begin to show signs of early deterioration coupled with flawed operation, resulting in on-going maintenance that could ultimately require its complete replacement,” notes Vlahos. Similarly, choosing good quality building materials and systems for the windows, doors, and frames is obviously the best way to minimize maintenance. In addition, savvy Building Teams advise owners to insist the design team or contractors provide a maintenance schedule for materials and products. Generally speaking, an annual inspection of window frames and doors is an excellent way of identifying areas requiring attention. In Smith’s opinion, careful installation is the best preventative.
“If the installer doesn’t adhere to the manufacturer’s installation instructions, the window will be doomed to disappoint,” he says. “Air and water leaks and binding frames are most often the result of a poor installation, which might also include inadequate structure around the window, placing unanticipated stresses on the window unit.”
Of course, even a perfectly installed system will degrade over time from exposure to the sun and water. Consequently, anything that minimizes this exposure, such as more durable protective coatings or roof overhangs, will ensure greater longevity. Buck lists the following specific concerns that require periodic maintenance: Repairing finishes to prevent corrosion; Lubricating and servicing moving hardware parts; Replacing surrounding sealants and flashings; Replacing failed hardware before it damages the window or door. • Replacing work weatherstripping; Preventing vandalism. Moreover, Schmidt points out the latest International Building Code actually requires owners to document periodic inspections of their buildings’ fire-resistance-rated door openings. This is quite a shift from the previous code and will add to owners’ O&M costs. While windows and doors are constantly improving in terms of design, performance, and sustainability, by investing the proper time and resources into system selection and installation, Building Teams can help open a new door into the world of high quality, performance, and longevity.
SIDEBAR: The Promise of Powder Coating One of the most notable emerging technologies in the realm of eco-friendly door and frame finishes is powder coating. In addition to enabling the use of higher recycled content with aluminum products by lending a more even color appearance and a harder finish, powder coating is more efficient in that overspray can be recovered and application temperature and drying times are less restrictive.
“An added benefit to the new powdered fluoropolymer coatings is their application process,” explains Duo Dickinson, AIA, NCARB, a Madison, Conn.-based architect. “Solvents are not used, making them VOC-free, thereby further reducing energy usage and eliminating carbon emissions.”
Mark Schmidt, a specification writer/coordinator with Fanning/Howey, Celina, Ohio, also sees promise in powder coatings. He points out, however, the process is still relatively expensive and time-consuming and not as durable or weather-resistant as other finish applications.
“Bright colors that have been applied using the process of powder coating often fade within a few years since most are not currently as resistant to ultraviolet radiation as spray finishes,” he warns.
Are you interested in earning additional AIA/CES learning units? Visit www.BDCuniversity.com for three courses: Building in Coastal Regions: High-Velocity Hurricane Zones, Design Criteria for Windows + Doors • Windows + Doors: Daylighting, Passive Solar, and Energy Modeling as well as many other courses
This completes the required reading for this course. To earn 1 AIA/CES continuing education unit, complete the required reading and take the CEU test.
HIGH-PERFORMANCE WINDOW/DOOR EDUCATION MODULE
Pass this exam and earn 1 AIA/CES credit!
1. According to a recent Building Design+Construction survey, the most important factor in product selection and system design for windows is: A. Aesthetics. B. Durability and reliability. C. VOC content. D. Energy and thermal performance.
2. A thermal break helps resolve heat-conduction problems in aluminum and other fenestration frame materials. The frame is split into multiple components and connected by: A. A layer of insulation B. A less conductive frame material C. Elastomeric caulking D. None of the above
3. To create thermal breaks, window and door manufacturers currently produce separate interior and exterior aluminum profiles joined together with polyamide extrusions that reduce the potential for structural damage because—relative to aluminum—the thermal break’s coefficient of expansion is: A. About the same B. Significantly higher C. Significantly lower D. Zero
4. For vinyl, fiberglass, and composite door frames, thermal performance is often achieved through multiple-chamber designs, which incorporate: A. Wood spacers and insulation B. Insulation only C. Air spaces or foam insulation D. Chambers filled with air or argon only
5. Continuity of air barriers and membranes around the window-wall interface or door-wall interface provides jamb assemblies that: A. Reduce air leakage and moisture intrusion B. Increase the durability of the building enclosure C. Improve the thermal and energy performance of the building D. Achieve all of the above
6. To protect the integrity of enclosure air-barrier systems, the head, jamb, and sill should be detailed so there is no penetration of the flashing or air barrier materials by: A. Weepholes or other moisture drainage elements B. Window fasteners or anchors, such as receptors and subsills C. Vents, chimneys, or flues D. None of the above
7. Pan flashings manufactured for window assemblies should protect against water intrusion, but Building Teams should review end-dam and back-dam detailing within the wall cavity to ensure that factory assemblies provide: A. Proper seal and minimum height per ASTM standards B. Minimum heat gain and moisture resistance per code C. Conformance to ADA requirements D. All of the above
8. Where noise control is a primary concern, engineered insulated metal doors and wood doors can achieve sound transmission class (STC) ratings of: A. About STC 45 for insulated metal doors and STC 57 for wood doors B. About STC 57 for insulated metal doors and STC 45 for wood doors C. About the same STC values for both insulated metal doors and wood doors D. None of the above
9. True or false: The performance of door closers is described in ANSI/BHMA standards. A. True B. False
10. Doors larger than what standard dimensions require heavy-duty hardware? A. 24 inches by 6½ feet B. 36 inches by 6½ feet C. 24 inches by 7 feet D. 36 inches feet by 7 feet