An extensive amount of local sandstone - accented by Indiana limestone trim - was used in the renovation and expansion of the Koelbel Building, which houses the University of Colorado Leeds School of Business in Boulder, CO.

When the time arrived to renovate and expand the Koelbel Building, which houses the University of Colorado Leeds School of Business in Boulder, CO, the desire was to create a design that would stay true to the “Tuscan Vernacular” style of architecture that is prevalent on campus. To accomplish this task, the design team relied on a blend of Colorado sandstone, which was quarried at various sites in the region.
The design goal from the exterior point of view was to fit into the context of the existing campus - rubble sandstone trimmed with white limestone,” explained Robert Quigley, AIA, principal at ARC/Architectural Resources Cambridge of Cambridge, MA, the design architect that collaborated on the project with Davis Partnership Architects of Denver, CO. “It is a palette of materials that was developed back in the 1920s.”
Quigley went on to say that up until 1918, the buildings at the University of Colorado had been constructed using different architectural styles. “At that time, the University hired Charles Klauder, an architect from Philadelphia, to develop a comprehensive master plan for the campus,” he said. “This plan led to Klauder’s proposal to create a signature architectural aesthetic for the University. Preliminary Klauder studies referenced the common style of the period - namely English Collegiate Gothic as seen at Princeton and Yale. However, he quickly discovered that the local stone in Colorado could not be quarried in a way that complemented this style.”
As a result, Klauder had to rethink his initial design concepts - even traveling to Europe for ideas. After careful deliberation, the architect developed, what he termed, the “University of Colorado style.” This style, which has since become known as “Tuscan Vernacular” was soon implemented for all new buildings on campus.
To achieve this style of design, Klauder relied on a mix of local sandstone. “There are four kinds of stone in each building’s palette,” said Quigley, adding that the color range for the new building consists of 60% red, 20% pink, 15% variegated and 5% buff. “In order to get the appropriate mix, the sandstone came from a variety of local quarries.” He explained that using local materials is one of many sustainable aspects of the project that helped the Koelbel Building achieve its notable LEED Gold Certification through the United States Green Building Council (USGBC).
Quigley explained that although the mix of sandstone lends itself to a “rougher” style of design, there are also more classical elements such as columns and traditional architectural details. “The campus context has evolved significantly over the years,” he said. “What is really unique, I think, about the University of Colorado is that they were committed to keeping this style. While some campus buildings have used these materials in a contemporary way, the proximity of the Leeds School building to a more historic part of the campus influenced the final design solution which reflects the principles of Klauder’s Tuscan Vernacular style.”
The facades of the buildings on campus that were constructed in the 1970s are pinker in color, according to the architect. “Our goal was to return to the more historic look of the original buildings, which are redder,” he said. “This proved to be a challenge as many of the quarries had changed over the years.”
The sandstone pieces used for the new Koelbel Building range in size. “The pieces are all different sizes,” said Quigley. “The school has guidelines how these stones are set, including how large a stone can be - only 7 to 8 inches vertically maximum. They are very disciplined in their approach. It all depended on how good the masons are on the job.”

The objective was to create a design that would stay true to the “Tuscan Vernacular” style of architecture that is prevalent on campus.

Paying attention to details

The design team from Davis Partnership Architects was on site at least once a week to observe the progress of construction, according to Brian Erickson, Principal-in-Charge. “We required a free-standing mock-up to be constructed on the site prior to the installation of any stonework,” explained Erickson. “There were several critical design aspects of the stone that we were interested in verifying through the construction of a mock-up.”

In particular, the design team paid close attention to the color and size blend of the ashlar sandstone exterior walls. “The mock-up gave us an opportunity to verify that the color blend and texture we were aiming for was achieved,” said Erickson, adding that the mock-up also allowed them to make sure that the criteria for the lay-up pattern was followed.

Reiterating Quigley’s words, Erickson explained that the University Facilities Planners had developed very specific criteria and parameters for laying up the ashlar pattern. In addition to setting a maximum and minimum thickness of any individual stone and maximum thickness to length ratio, there were specific rules set for convex versus concave split faces, maximum number of stone courses abutting “jumpers,” a maximum and minimum range of dimension that the stone face should extend outward beyond the plane of the mortar joint, and outside corners are struck vertically in alignment.<br><br>
“The mock-up gave us an early indication that the mason understood and was able to execute the criteria,” said the architect. “It also gave us an opportunity to verify the color consistency of the limestone accents and that they were being placed as detailed.”

Overall, Erickson explained that they were fortunate to find a good mason. “Although the masonry subcontract was competitively bid through the Construction Manager/General Contractor, we pre-qualified the list of bidding masonry subcontractors - each of whom had some experience working on the CU-Boulder campus,” he said. “We are fortunate that the Denver market has many highly skilled masons.”

Before work on the project began, the design team visited several area stone yards to determine what colors were being extracted from the local Colorado quarries, according to Erickson. “We were looking for a level of consistency in color for each type we were considering specifying as part of the overall blend,” he said.

One of the most challenging aspects of the project, in regards to the stonework, was the schedule, said Erickson. “With the smaller stone sizes and patterning criteria and the production of stone peaks at about 25 square feet per mason per day, keeping pace with the expectations of the overall construction schedule was the most challenging,” he said. “Fortunately, the mason was experienced with the requirements from previous work on the campus and did not need a lengthy learning curve to get multiple crews up to speed.”

In total, construction of the Koelbel Building expansion was completed in 17 months. “The design team had a considerably shorter time to design and document the project; and due to time restrictions, we issued three separate bid packages of construction documents in fast-track fashion,” said Erickson.
According to both architects, the Business School has been elated with the success of the project. “The Dean recently reported a doubling of enrollment in the school’s executive education program since they moved into the completed building,” said Erickson.