BOULDER - When it comes to defining class A office buildings, it may appear that the "A" stands for "amorphous."

In general terms, it is the upper crust of office space, which fetches the highest tier of lease rates. But the actual attributes vary regionally, with market demand and building limitations combining to create a Boulder classification.

The leading national trade organization for the office building industry surveyed its members in 2005 and created a standard definition of class A buildings. (See 37A).

But the definition ended with this qualifying statement: "Because property characteristics in different markets vary dramatically, property class definitions will remain subjective."

"In Boulder, many of the buildings that fit this definition are much smaller than the typical mid-rise office tower that is found in office parks such as Interlocken, DTC, Inverness, Greenwood Plaza, Meridian and downtown Denver's central business district," said Mark C. Stoldt, a commercial real estate appraiser with Boulder-based The Rothweiler Group Inc. "In addition, many of the buildings that have class A quality are in mixed-use properties that share street-level retail and upper-level residential."

Local class A spaces are leasing in the range of $18.50 to $24 per square foot, triple net, according to Becky Gamble, real estate broker and president of Boulder-based Dean Callan & Company Inc. An additional $10 to $11 per square foot for estimated expenses covers shared expenses such as professional management, janitorial, common area maintenance, property taxes and building insurance.

"Most class A buildings have steel structures with lots of glass and impressive lobbies," Gamble said. "Tenants usually include banks, financial institutions and law firms."

New construction is not necessarily a requirement, according to Gamble. "So long as the owners are keeping the building updated with high-level finishes in the common areas, lighting, ceiling treatment, etc., there is not really an age limitation to be class A."

Green building is a growing trend with Leadership in Energy Environmental Design, or LEED, certification often included in new class A office buildings. "It has caught fire," said Brad Power, redevelopment director for the city of Boulder. "A lot of the larger firms are hiring people to focus on that exclusively."

Good examples of class A buildings in Downtown Boulder are One Boulder Plaza and the 1050 Walnut building. The new project by Tebo Development - under way next-door at the old Oasis Brewery site on Canyon - will include high-end office space.

Outside of downtown, several class A office buildings are clustered around the Twenty Ninth Street retail district including 3100 Arapahoe and Water Street Plaza at 26th Street and Canyon Boulevard.

Close to Water Street, a major redevelopment is in the works for the site now housing the Golden Buff Lodge and Eads News & Smoke Shop. The Canyon 28 project will include three buildings with underground parking, 62,000 square feet of retail on the ground floor and 284,000 square feet of office space on the three stories above. It's a co-development between Denver-based Urban Frontier, Texas-based Granite Properties and Lou DellaCava's LJD Enterprises, based in Boulder.

Designed by OZ Architecture, the plans go before the city's planning board for site review in October. Urban Frontier's Stephen Moyski said the developers hope to break ground in the first quarter of next year and deliver in late 2010. They are aiming for LEED silver certification, or higher, he added.

No tenants are lined up yet, but according to Moyski the target market is "larger employers in Boulder who don't want to relocate down the corridor when they outgrow their space."

There is a shortage of class A space for larger users in Boulder, said Power, because of a lack of vacant land, combined with height and other construction restrictions. "We can't go out and do a 10-story building like they can in Broomfield," he said. "The positive side to that is that the firms that want to have a Boulder presence, they seem to find a way to do it."

So far, the outlying communities within Boulder County have not filled the void.

"I would have to say there are really no class A spaces in Longmont, Louisville or Lafayette," Gamble said. "There are nice office buildings in those areas, but just based on size alone, none can really be considered class A."

That may change in the future. John Cody, president of the Longmont Area Economic Council, said developing class A office space will be the new focus of one of his board committees.

"Interlocken is becoming built out," he said. "There's going to be a market for it."