Architects who have done multi­family work know the project type differs from single-family in profound ways. Instead of designing for homeowners looking for a great place to live, architects with multifamily commissions must collabo­rate with developers, for whom small decisions can have major financial ramifications. As a result, important choices such as window selection become even more significant, because the architect must consider the pro forma and profit-and-loss implications of every aspect of the design.

“There are clear technical differences” between specing windows for a house and for a multifamily building, says Douglas Stockman, a principal at Kansas City, Mo.-based el dorado. “From a design perspective, it depends on whether a project is a rehab versus a brand-new building or an apartment versus a condo. Acoustic quality is important in multifamily work, and price is also a big deal.” For architects who have a favorite window spec, the chances of having the brand approved often are slim—particularly if the product is on the pricey side. In those cases, he explains, “it’s hard to hold on to a manufacturer.”

window worries Windows are a particularly tricky spec, because they are so central to architecture and contribute so greatly to inhabitants’ quality of life. Important for views, light, and fresh air, windows also must successfully block heat gain and prevent heat loss. But selecting the right ones involves more than sight lines and energy issues. “We look at production issues, maintenance, and liability for the owner,” says Jonah Busick, LEED AP, a director at Phoenix-based merzproject, a studio of Shepley Bulfinch in Boston.

Choosing windows for buildings in dense urban locations raises even more issues, says developer Michael Lander, president of Minneapolis-based Lander Group. Sound transmission ratings, installation, and durability are important considerations. Although Lander may choose lesser-quality windows on entry-level projects to meet the budget, his company always looks for a certain level of aesthetics and performance, no matter the price point. “Windows are really important to the building envelope,” he says. “More windows also raise the bar for the overall quality of the design.”

Lander’s brand of choice is Marvin Windows and Doors. If cost is an issue, he specs low-E units from the company’s Integrity line. A step up from vinyl, Integrity products can be made entirely from Ultrex fiberglass or with fiberglass exteriors and pine interiors.

Some architects and developers choose traditional residential windows for their mid-rise projects, while others favor commercial systems. Busick says merzproject typically uses all-aluminum windows and storefronts with thermally broken frames, such as those from Kawneer North America and Arcadia Architectural Products. “A lot of people are drawn to [storefronts] because they aren’t accustomed to seeing them in a residential setting,” he explains. “We have had a great response from both the buyers and the developers.”

One residential window manufacturer known for its multifamily-friendly alumi­num products is Milgard Windows & Doors. The company says its products are especially popular with architects seeking windows with narrow profiles and that fiberglass is becoming more common in multi­family work because it also can be offered with thin frames and in dark colors.

Aluminum also is the preferred spec for el dorado’s multi­family work, but the firm is more flexible on system types. It uses such windows for rehab buildings, for example, to preserve any industrial character, but “other times we may use storefronts or residential wood systems with metal cladding,” Stock­man says. One favorite is EFCO Corp.

Fortunately, architects have at their disposal many traditional brands that can be used in mid-rise multifamily projects, including Andersen Corp., Kolbe & Kolbe Millwork Co., and JELD-WEN. One not-so-new player is YKK AP America, which produces residential vinyl windows and aluminum commercial systems. Its newest product, the YOW 350 T, is an architectural-grade window with triple glazing and integral blinds for heat gain control.

Another innovation in window design comes from the Netherlands, where Amsterdam-based Hofman Dujardin Architecten hit upon a new approach while looking for a way to maximize floor space in apartment buildings. “We thought about the former Amsterdam warehouses, whose façades opened up” so workers could “load the warehouses directly from the canal boats,” explains principal Michiel Hofman, who designed the concept with partner Barbara Dujardin. “Then we tried to integrate the rear end of a truck in a façade.”

The firm’s invention, Bloomframe, is essentially an insulated steel, glass, and aluminum picture window that can be converted into an open balcony. Suitable for new and retrofit buildings, the motor-controlled “balcony-on-demand” is being produced for apartments in the Netherlands. It likely won’t be available in the United States until 2011.

learning the drill These days, architects doing multifamily projects may spec whatever type of window they want, so long as it meets code requirements. “The standard for windows, doors, and skylights no longer recognizes ‘residential’ or ‘commercial’ windows,” explains Ken Brenden, technical services manager for the American Architectural Manufacturers Association, but “it does provide a general guide in determining which performance class is likely suited for a particular application. The higher classes typically are associated with mid- and high-rise construction, the lower with one- and two-family dwellings and low- and mid-rise multifamily dwellings.”

Although architects likely know what the codes allow and forbid, experienced design pros also have developed personal checklists of do’s and don’ts and have a sense of which specific issues to keep in mind when researching window options. Stockman, for example, says el dorado mainly specs operable systems for its projects to facilitate the circulation of fresh air.

Meanwhile, merzproject uses only thermally broken aluminum frames for energy efficiency and applies the same orientation techniques in multifamily façades that it uses for houses. “We do a lot of building modeling on window placement and exposure, so we use overhangs to help avoid direct sunlight,” Busick says. The firm also is reassured by at least one aspect of commercial products: “The nice thing about storefronts is that [the suppliers] do the installation,” he says. “They are very familiar with these systems.”

Stockman considers himself a fan of commercial systems, but he cautions architects to be mindful of the products’ susceptibility to defects. Residential windows are less likely to leak, he explains, because they come pre-assembled, whereas “commercial windows are cut and fitted on site, so end dams, flashing details, and corners are potential” problem areas. Consequently, he continues, installation is key: “A lot more windows leak than you know, but they leak into cavities,” so the damage isn’t seen. As a preventive measure, he “highly recommends” architects have any system they spec tested for leakage early enough to ward off potential problems.

Because even the best windows will leak if not installed correctly, Lander’s company holds “drill” meetings to discuss how to go about it. After all, he says, “It’s not just the window—but how the window is installed—that makes the difference.”