Boston high-rise finds perfect fit in unitized curtain wall system

Choosing the right vision glass is also critical in making a coherent visual statement. In most lighting conditions, the spandrel glass can blend in with the vision glass when the latter has either a higher reflectivity or darker color. By increasing reflectivity, it is possible to adjust the average for every piece to appear closer to the designed values of hue, reflectivity, and the like. Since the Raffles client group desired a lower reflectivity, the project
team had to strike a delicate balance.

The solution was to slightly increase the reflectivity and then compensate by moving to a darker vision glass color to blend with the spandrel glass; it would not be fully black or brown, rather, a warm tone with hints of bronze which picks up the tone of the composite metal panel trim. Further, the deeper hue and reflectivity level of this glazing offers the benefit of differentiating the Raffles tower’s appearance from the bright blue, highly reflective curtain wall of the Hancock—providing a respectful and complementary foil to this iconic neighbor. Another advantage of these choices was its improved solar heat gain performance, which helped the tower meet local code-mandated requirements for a Leadership in Energy and Environmental Design (LEED) gold certification.

Acoustic solutions

Designing a curtain wall system for hospitality brings interesting and unexpected constraints beyond aesthetics. To maintain a comfortable and luxurious interior environment, the Raffles Hotels & Resorts brand requires strict limits on the amount of outside noise transferring through the exterior wall into the building interiors. Controlling the Outdoor/Indoor Transmission Class (OITC), which is essentially a Sound Transmission Class (STC) rating system for exterior wall, is complicated by a curtain wall design, as it cannot receive added insulation or denser substrates to increase acoustical performance. The same is the case with many opaque assemblies.

For this project, the design team found another creative solution. A standard glazing unit with a 25.4 mm (1 in.) sandwich of glass and argon gas, comprising 12.7 mm (0.5 in.) of airspace, with a 6.35 mm (0.25 in.) glass pane on either side. An acoustical consultant assisted in devising a glass assembly to mitigate as much sound as possible within these dimensions.

The result was an asymmetric assembly in which the outside face of glass is 7.94 mm (0.3125 in.), and the inside pane is slightly thinner than 6.35 mm (0.25 in.). This very small increase over the standard exterior thickness proved to have a significant positive impact on the level of noise transferring from the outside, and the balance of the asymmetry notably mitigated external sounds without affecting the depth of the glazing pocket within the extruded aluminum mullions.

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