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When it comes to selecting fenestration systems—particularly glass facades and door systems—a number of factors come into play, requiring a thorough evaluation of a project’s individual requirements. However, some general guidelines can be helpful to get started.
Since door systems fall under the most “operable” part of the design realm, durability often tops the list of key considerations when selecting a product type, says Mark Schmidt, RA, CCS, LEED AP, Specification Writer/Coordinator, Fanning Howey, Dublin, Ohio. However, many project team leaders such as Duo Dickinson, AIA, NCARB, CORA, a veteran architect based in Madison, Conn., rank restorability as their number one concern.
“Many doors that look good in the showroom look horrific in one or two years,” says Dickinson. “Doors are by their nature cantilevers and thus handle a great deal of ‘dead load’ that tends to wrack the entire panel of the door.” Since even the best of doors will undergo a certain amount of wear and tear, a system that responds well to maintenance is essential.
Cost and aesthetic appeal are two other crucial factors that must be taken into account. Specifiers also need to understand the door’s anticipated function, which encompasses volume and type of traffic. Meanwhile, external and internal air forces created by wind, HVAC pressures, and seasonal changes—which can cause the door to expand or contract—must also go into the equation.
After reading this article, you should be able to:
- DISCUSS the basic materials and product types available for commercial glass systems, entrances, and doors as they relate to occupant safety, environmental factors, and durability.
- COMPARE storefronts, window walls, and curtain walls in terms of application types and performance characteristics, especially with regard to energy performance.
- LIST considerations for glazing selection for commercial glass façade systems in terms of human health, indoor environmental quality, and safety.
- EXPLAIN how to resolve performance attributes, system limitations, and sustainability requirements for glazed openings and entries in typical building projects.
In fact, the Window & Door Manufacturers Association recently approved a new standard, No. 300-12, for the installation of exterior doors where there is “extreme wind/water exposure.” Joined by the Fenestration Manufacturers Association and the American Architectural Manufacturers Association, the WDMA says the standard is “specifically designed for installations subject to extreme wind/water climate exposure, particularly in the coastal southeastern United States.”
Mark Heinaman, co-founder of Las Vegas-based Heinaman Contract Glazing, lists safety, code requirements, water and air infiltration resistance, seismic and live-load deflection, and hardware compatibility as top considerations for Building Teams.
Other professionals state that the choice of hardware should be an early consideration for door selection. For example, many projects are often frustrated by faulty hardware packages, says Dickinson. “We have found that sometimes very well-made doors have undesirable hardware and occasionally have to work with blank doors and retrofit better hardware into them,” he says.
In any case, once these variables are sorted out, the Building Team can move on to choosing between different door materials, each one with its pros and cons.
Wood—Beautiful but vulnerable. While it’s difficult to rival the warmth and beauty of genuine solid wood and wood-veneered doors, the material’s Achilles heel is undoubtedly weatherability. Consequently, wood is frequently reserved for doors within interior public spaces, or for exterior uses where other potential problems, such as aesthetics or historic matching, are the main considerations.
Woods exposed to the elements undergo three types of weathering forces, writes William C. Feist, a research chemist with Forest Products Laboratory, Madison, Wis., in a research summary from the 1980s. They are: 1) sunlight, which causes photodegradation; 2) water, which causes leaching, hydrolysis, and swelling; and 3) microorganisms, which may cause discoloration and degradation due to staining and decay. Of course, wood can be protected by paints, stains, and varnishes; according to Feist, opaque paints provide the most protection to exposed wood surfaces.
More recently, according to Jim Berg AHC/CDC, CSI, BMA, principal of Door Hardware Consulting, Prairie Village, Kan., manufacturers have produced high-end wood door systems where the core construction—at around 2½ inches of thickness—doesn’t absorb moisture. These products can come with a high price tag, however.
Consequently, some specifiers may look for alternatives, just as architect Adam Zimmerman, AIA, LEED AP, recently did for a religious facility project. “When we considered both the maintenance risks and cost deterrents of true cedar doors, we decided to start looking for alternatives to real wood and landed at a stain grade fiberglass,” says Zimmerman, principal of Zimmerman Workshop, Brooklyn, N.Y. “The product we selected is a fully insulated door with a subtle woodlike grain that is able to absorb a stain for the look and feel of wood without all the headaches.”
Fiberglass—Strong, easy to maintain. While not one of the more classic door material choices, fiberglass offers the benefits of strength, low maintenance, and resistance to denting and scratching.
“Aluminum doors with insulated cores and clad with fiberglass-reinforced polymer are attractive, colorful, and abuse-resistant,” says Fanning Howey’s Schmidt. “They can be used at secondary exterior access points where knowing what’s on the other side of the door is not as important as at main entrances.”
Metal—Flexible, but hold the salt. As for exterior entrances, glazed aluminum is frequently the system of choice for its weather resistance and visibility. “A metal door or a storefront-type door extruded in aluminum, bronze, or similar materials can provide the best flexibility in exterior applications in an offset configuration of the door and hardware,” states Contract Glazing’s Heinaman. “This particularly helps in achieving values needed for air and water infiltration.”
One environment where metal doors don’t perform well is in coastal or other saltwater conditions, as even the best paint or anodized finish will usually begin breaking down over time, according to Dickinson.
Another limitation of the metal/glass combination is its ability to resist heat transfer. Consequently, when fire resistance is a requirement, then hollow metal doors––with or without insulated cores––are a strong, economical, and secure choice, says Schmidt, based on his 25 years of experience specifying door systems. He notes, however, that the tradeoff in this case may be aesthetic appeal.
Glass—Modern touch, but heavy. While glass doors go a long way toward creating a beautiful, modern look within a space––not to mention enhancing natural light––their application as exterior doors is somewhat limited as they don’t seal well against water and air infiltration. In warmer settings, an overhang should be installed to protect the door from blowing rain.
Another difficultly is the weight of a glass door. That’s why metal frames are much more common than wood for glass door systems, as the metal corners can transfer the glass weight load to the hinge side of the door, according to Dickinson.
Curtain wall vs. Storefront--when size does count
Automatic and revolving door systems are generally integral to a glass and metal façade system or storefront. Moving beyond the front door, these glass components of the building’s façades are a major architectural design element. Curtain wall, storefront, and window-wall systems are highly competitive—even redundant—and employ very similar assemblies and materials.
Because these glass enclosure systems each have specific criteria for their basis of design (BOD), Building Teams must consider function, aesthetics, performance characteristics, and system limitations for the specific project at hand as guidelines for initially choosing a system. However, certain general guidelines apply when it comes to a specific building type.
“Generally, the size of an opening is one of the biggest determining factors for using storefront or curtain wall,” says Allen Cradler, AIA, CCS, LEED AP BD+C, a project manager for Fanning Howey. “Openings 10 feet to 12 feet high are about the maximum for typical storefront systems.” Common aluminum-and-glass installations can span floor to ceiling, or can be installed as fixed windows set into brick, stucco, EIFS, or precast concrete openings, and are usually limited to one- and two-story buildings due to the system’s wind-load resistance limitations.
“Typical aluminum storefront framing systems using monolithic or insulated glass generally are low-performance systems, having limited capacity to control water and air infiltration, and no means to control secondary water from the surrounding conditions at the head/top of the window opening,” explains Kirk Osgood, Principal and Senior Vice President, Curtain Wall Design & Consulting, Dallas. This being the case, Osgood––based upon his 40 years’ experience in the curtain wall industry––recommends these storefront systems exclusively for projects where the expectations match the performance, such as retail and restaurant settings. In these cases, the system would be installed with a pre-engineered subsill component for better sealing.
With window-wall systems, a higher level of performance can be expected and the aesthetics can be clean and modern. At the same time, there are a limited number of suppliers and options for these products, reports David Walker, Vice President of Association Services with the National Glass Association, Vienna, Va.
The head and sill of window walls can either be installed continuously or with vertical mullions that run through, with the horizontals cut in between the verticals. Berg prefers the continuous approach, as it provides the potential to design a system to collect, control, contain, and discharge the entry of secondary water from the head of the window surrounding conditions.
Curtain wall systems can be engineered to span greater vertical and horizontal distances; many provide built-in water management and weeps. In addition, curtain walls offer more flexibility with aesthetics, glazing selections, and structural integration, according to Cradler. However, curtain walls also are more expensive and require a highly competent contractor or installer. There is greater potential for site-assembled and even prefabricated curtain wall products to present leakage issues if installed poorly or inconsistently.
Windows and Doors: Do they match?
While custom-designed and custom-manufactured window and door products are the most surefire way to ensure that all windows and doors on a given project are a visual match, there are other options.
In some cases, it may be sufficient to use similar framing systems such as hollow metal or extruded aluminum, according to Mark Schmidt, RA, CCS, LEED AP, Specification Writer/Coordinator, Fanning Howey, Dublin, Ohio.
While using the same trim for the windows and doors is another strategy, Schmidt finds wood trim on door frames highly vulnerable to damage. “Also, field-constructing wood frames with trim for doors is labor-intensive and prevents other work from taking place concurrently in the immediate area,” he says.
On a recent project, Adam Zimmerman, AIA, LEED AP, Principal of Zimmerman Workshop, Brooklyn, N.Y., had to rely on trim to match different kinds of doors and windows. Since his budget prevented him from specifying one type of fenestration, his team had to get creative with fiberglass doors, steel clad doors, and PVC windows.
The solution: Using painted steel doors on all upper balcony doors, which are physically separated from the lower fiberglass doors. “Ninety-five percent of visitors to the building never get close enough to the steel doors to notice the difference, and in no case are there two differing doors within direct view of one another,” Zimmerman explains.
However, when it came to the fiberglass doors and PVC windows, which were in direct proximity to one another, “We had to trim each out very carefully on both the interior and the exterior to create the aesthetic unity between the different products,” he adds.
Narrowing down the choices
In terms of what’s available, curtain wall comes as 1) a stick-built system, 2) a factory-assembled and glazed unitized system, or 3) a hybrid stick system with preglazed cassette frames. The preglazed hybrid types have fabricated frames that slide into field-installed vertical and horizontal framing members.
Stick-built curtain walls—right for smaller projects. With this design approach, the curtain wall’s vertical and horizontal framing members are installed on site as individual pieces, then filled in with glass or other infill materials. Although stick-built systems do require more on-site labor, if it’s a smaller project and doesn’t have a lot of repetitive modules, then it might be the right choice, according to Osgood.
“Vertical mullions generally span two floors,” he adds. “This twin-span design increases the dead-load reactions at every other floor line, so coordination with the project structural engineer to accept this increased loading is required.”
Building-integrated photovoltaics—on the road to net-zero
No discussion of the openings market would be complete without mention of glazing-related photovoltaics, especially with the net-zero building trend gaining momentum.
Essentially, the main problem with PVs is return on investment. “Currently, we expect a 20- to 30-year payback for thin film and all other photovoltaic systems,” says Dennis Hacker, AIA, CSI, CCS, CCCA, LEED AP BD+C, Specification Writer/Manager at Fanning Howey. “At that rate of return, these systems are limited to clients who either have extremely high energy costs, an unreliable energy supply, or a strong philosophical commitment to sustainability beyond just lowering operating costs. For the technology to gain broader acceptance, the payback period would need to be five years, maximum.”
Osgood points to aesthetic issues with PVs, the limited number of manufacturers producing these products, and the fact that the wiring requires penetration through the façade system, creating a potential for water infiltration. But the energy-efficient, sustainability-conscious building industry is nevertheless pushing for further development of the technology.
“This form of electric energy production will probably increase in the future,” says Osgood, “as there become more incentives, more manufacturers of viable commercially available products, and as greater returns on the investment are realized.”
Toward this end, industry leaders are partnering to better leverage their expertise and capabilities, in an effort to address these concerns. “The three keys for future progress are price, performance, and aesthetics,” says Walker. “The price has to come down to make it more achievable for the building owner or developer. The performance has to improve the ROI, and the looks have to be appealing to the architect.”
Unitized curtain walls—allow enough lead time. With unitized systems, the individual units are fabricated, assembled, and glazed in the factory and then shipped to the project site for storage and eventual erection. Because these systems are more complex and require more engineering, lead times are longer, as the majority of the work is done off site.
Osgood lists the reasons why a unitized curtain wall system is usually specified: project size, complexity of the architectural features, façade geometry, incorporation of exterior shading elements, performance criteria, project logistics, schedule, a desire for factory-controlled quality control, and the sophistication level of the curtain wall contractor and manufacturers.
One critical aspect of the fabrication process is ensuring that the gaskets in the horizontal and vertical mullions are sealed well with the framing members. In other words, the four-way intersection of these units must be continuously sealed if the system is going to meet air and water infiltration performance criteria. Once the curtain wall is installed, there is no way to access and correct these seals, so it must be executed correctly the first time around.
Although general guidelines are helpful, Osgood emphasizes that every project is unique in its own local access to materials, schedule, logistics, and location, in addition to requirements for air and water infiltration, thermal performance, wind loads, seismic movement, blast resistance, and acoustics, to name a few. Consequently, project conditions must be fully vetted before a system is chosen.
“The prudent architect or project owner, or both, would also be wise to enlist the services of an independent, qualified, professional curtain wall consulting firm experienced in all facets of the building envelope design and materials selection process,” he adds. “The consulting firm should be multilevel and multidimensional in capabilities and expertise, with a proven track record.”
There are also technological advances to weigh against cost and performance expectations, says Walker. For example, he sees unitized curtain walls making progress, with newer systems offering U factors below 0.30, with easier installation. In that context, Osgood calls out dual durometer and copolymer gaskets—as well as more extruded silicone gaskets—as components that are enabling tighter air seals and better compatibility with silicone sealants. Oswald says he is also pleased with the newer engineered subsills for storefront systems. However, because manufactures are still trying to utilize as little aluminum as possible, the jamb perimeter conditions in some cases may be inadequate to provide the proper perimeter sealant conditions for this component, he explains.
Window glazing--making continuous improvements
From dynamic glazing to vacuum-insulated glass to fourth-surface coatings, the glazing industry continues to make advances, particularly in the face of stricter Energy Star criteria coming down the pike in 2014. For example, Walker points to developments in the electrochromic and thermochromic glass industries, where a handful of well-established companies are busy researching, refining, and manufacturing both high-end electrically tinted glass (electrochromic) and heat-activated switchable surfaces (thermochromic).
“The key with all of these products will be improvement on the energy-efficiency side,” he says, noting that the manufacturers are working with industry partners to create myriad products and assemblies using the glazing types.
While thermochoromic and photochromic glass rely on chemical reactions to alter shading levels, electrochromics require electrical wiring, necessitating a higher level of coordination between the design team and the building trades, with MEP engineers playing a more active role, notes Osgood. “This involves more training and education to implement and more design to effectively incorporate the wiring into the framing systems,” he says.
Another goal currently being pursued by the industry is significantly boosting thermal performance to help counter the trend of decreasing window-to-wall ratios. One of the keys to achieving this may be vacuum glass insulation, which would potentially offer insulation levels equal to, or even greater than, triple-glazing, but only utilizing two panes of glass instead of three.
At this time, the technology is not seen as adequately cost-effective and may require further development to achieve anticipated performance, according to experts consulted for this course. Yet, the industry may very well see strides toward this end within the next couple of years.
Meanwhile, the industry is catching up with triple-glazed insulated glass units, as framing systems capable of handling the thickness of the glass in the glass pockets are now available, says Osgood. However, while triple glazing is becoming a more viable option in the residential market, it’s less common for commercial projects; only for commercial buildings in northern climates are triple-glazed IGUs specified with any regularity, according to the experts.
Dickinson offers a unique take on noteworthy hardware developments in the window industry. “The most exciting part of windows is the ever-more refined, easy-to-use, and durable hardware used, especially for casement windows,” he explains. “We’ve come a long way in the last 20 years.”
The right decision on glazing
Whether it’s choosing a door type or glass façade system, a project’s unique factors will always inform these decisions from a cost, aesthetics, and performance standpoint.
Only based upon the building’s intended use, climatic conditions, code requirements, building orientation, and other salient factors can designers and specifiers make informed decisions about what glazing solution will work best for a given facility. +
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