Volume 46, Issue 8 - September 2011

feature

2nd Annual USGlass Green Design Award Winner...

...and the winner is 1800 Larimer Street in Denver

1800 Larimer St. was developed to set a new standard in the Denver market. The Central Business District’s first high-rise office in more than 25 years became the first building in Colorado to be awarded LEED Platinum certification based on the LEED Core/Shell version 2.0 (which has more stringent requirements than earlier versions). The 22-story building was clad in glass to maximize the sweeping city views. But the developer also wanted to maximize the energy performance of this building, which meant careful selection of the glass products used.

“Westfield, the developer, wanted a sustainable building from day one,” recalls Ron Izzo, associate principal at architectural firm RNL and project designer on 1800 Larimer. “Our design approach strives for each project to try and achieve a LEED-certified level, regardless if it would ever be submitted for certification. For 1800 Larimer, we started with pursuing Silver. As we got further into the design process, the client would challenge us by asking, ‘What would get us to Gold? Platinum?’ Working with the client to achieve these goals was challenging in a good way.”

Selected as specialty glazing contractor, Harmon Inc.’s Denver team worked closely with the general contractor, MA Mortenson Construction, and RNL to meet the project’s pre-certified performance criteria, while maintaining the approved aesthetic.
The property showcases 9 1/2-foot-high, floor-to-ceiling glass, allowing for 92-percent natural light and unobstructed mountain views.

Performance Benefits
“We began our studies by looking at the building in the uniform skin of pre-cast and glass,” Izzo says. “Using a subtractive design process, we created voids and filled them in with the contrasting blue glass. This gave us the right visual balance with the gray glass set in a pre-cast spandrel. Each blue glass module is a repetitive, derivative of the smallest module within the building, which, on a standard office building is typically five feet. The modules then combine to fill the column bay, this is typically 30 feet from column-to-column and 14 feet from floor-to-floor. The pattern grows or shrinks in multiples of these structural bays, evolving around all four sides and spreading across all elevations. All of the blue glass modules stand off of the skin.”
According to information provided by the glass fabricator, Viracon in Owatonna, Minn., a great deal of planning was put into the glass selection, in an effort to “right-size” the glass. This, says the fabricator, resulted in a green, sustainable building with enhanced occupant comfort.

To create pleasant, daylit interiors without glare or thermal discomfort, Viracon helped create a unique glazing solution. Gray insulating glass with a low-E coating is the primary glass. The glass has a visible light transmission of 23-percent to allow enough light inside without glare or significant solar heat gain. This glass is broken up by large squares of blue insulating glass. The blue glass has a lower light transmission (8 percent) than the gray, but casts a beautiful contrasting light into the building.

The lower light transmission of the glass allows for daylighting effectively, without glare. With no glare, occupants do not need to supplement daylight with artificial light, which helps control energy usage.

The glass also offers an enhanced solar performance.

“The glass has a remarkable shading coefficient, which keeps solar heat out of the building,” says Cameron Scripture, Viracon’s Colorado sales representative. “This plays a significant role in contributing to the building’s energy efficiency and LEED goals.”
The gray glass has a solar heat gain coefficient (SHGC) of 0.23, while the blue offers a SHGC of 0.16. This high solar performance was chosen to help decrease HVAC system requirements and reduce overall energy consumption.

The Systems Installed
To accommodate the construction schedule and installation needs, the majority of the material for the project was fabricated and pre-assembled as a unitized system. Wausau Window and Wall Systems in Wausau, Wis., manufactured 164,000 square feet of the tower’s high-performance systems.

“To add the desired visual interest to the vast expanses of curtainwall, a four-sided structural silicone glazed Wausau 7250-UW unitized system was ‘projected’ out 10-inches from the face of adjacent walls, in randomly located accent bays,” says Steve Fronek, Wausau’s vice president of technical services.

The units were factory-glazed and furnished with three-way-adjustable, “jack bolt anchors” in Halfen® embeds to speed building enclosure. “Interlocking, pressure-equalized, internal rainscreen gutters ensured weatherability at extremes of inter-story dynamic movement,” Fronek says.

He continues, “At typical wall areas between accents, Wausau 6250i-RX window wall was anchored to pre-cast concrete spandrel panels. Window wall units were factory-glazed, and incorporated a two-level, thermal barrier design for energy efficiency and condensation resistance. Continuous sill starters ensured the continuity of perimeter sealant lines with adjacent curtainwall and setback wall panels. Intake louvers also were factory-installed by Wausau.”

Wausau, Wis.-based Linetec finished the aluminum framing and trim of the various systems in black anodize using an eco-friendly anodize.

Linetec also provided a matching finish for the building’s doors, supplied by Tubelite Inc. in Walker, Mich. At the main entrance, visitors pass through a glass revolving door to enter the two-story, glass-enclosed lobby.

Dynamic Design
With a multi-colored glass façade that constantly changes with the light of day, 1800 Larimer is a visually dynamic design. But the most dynamic aspect of this project is its energy savings, which—due to a combination of factors—the designer expects to be reduced by 30 percent when compared with traditional, downtown Denver office buildings. The project well demonstrates that glass can be an effective solution for designing energy-efficient buildings.

“As energy codes increase, a designer’s initial reaction may be to reduce the amount of glass on the facade to improve the overall wall performance,” Scripture says. “This is not the only way to meet increasing energy codes. Through conscientious design, including looking at the building as a whole system rather than individual components and specifying higher performing glass products, a high window-to-wall ratio does not need to be sacrificed to meet energy codes. The 1800 Larimer project is a testament to this.”

Thanks for Voting!
Earlier this year, USGlass sent out a request for submissions to its 2nd Annual Green Design Awards, and received in reply a wide range of project profiles that demonstrate the many innovative ways in which glass can contribute to a building’s sustainability, energy-efficiency, environmental conscientiousness—in short, overall “greenness.”

Our judges were asked to review all submissions to choose the one they felt best showed how glass can be used as a green and sustainable part of a building. After much deliberation, our judges selected three finalists for the USGlass Green Design Awards. From there, readers of the August issue of USGlass and the daily USGNN.com™ newsletter—and members of the growing online USGlass community via Facebook and Twitter—voted for the project they felt best represents the green attributes of glass.

Visit www.usglassmag.com to learn more about how you can get involved.

 

 

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