Raised Floors: A Green Building Advantage

Raised Floors: A Green Building Advantage

Toothaker, James S

In 1993, the Commonwealth of Pennsylvania’s Department of Environmental Protection occupied the newly constructed Rachel Carson State Office Building, a traditional 16-story government office structure. When it was designed in the early 1980s, green buildings were unheard of. Raised-floor systems were used extensively in computer rooms; the rationale for their use was to make it easier to accommodate wiring and cabling changes. The Carson building was typical for the time: modular furniture, full-height demountable walls, a variable air volume HVAC system with ceiling air distribution – and no raised floors. The construction cost was slightly more than $40 million.

In the years since the Carson Building was completed, it has seen plenty of internal reconfiguring – an estimated 375 work stations per year. What’s more, the state has begun to focus on green design in new construction. A look at what the Carson building missed shows how raised floors can help make a design both green and cost- effective.

A raised-floor system has lots to offer green building design. The big benefit is that it creates an under-floor plenum for HVAC air distribution. Occupant-adjustable air diffusers in the floor allow individuals to adjust temperature and ventilation in work areas while the constant-volume, low-pressure distribution system provides consistent temperature, good ventilation and humidification, and good indoor air quality throughout the facility.

The raised-floor system also provides an estimated 20 to 35 percent energy savings compared to ducted ceiling systems.

In addition, recent research suggests that, in new construction, first costs of under-floor air systems are equal to or lower than ceiling HVAC systems. This is because under-floor systems usually have smaller piping, pumps and refrigeration equipment, and the majority of ductwork is eliminated. One study estimated underfloor air systems cost $2.70 per square foot less than conventional systems.

But this green option for sustainable buildings also has much to offer facilities in terms of reducing churn costs. The HVAC system, wires and cables in the under-floor plenum are accessible through individual moveable carpet and floor tiles. These capabilities, coupled with demountable wall systems and systems furniture, provide the foundation for many years of cost-efficient churn.

Churn Cost

In today’s work environment, churn is a major issue. A 1997 survey by the International Facilities Management Association (IFMA) determined that, on average, 44 percent of occupants move per year. In government buildings, this churn rate is 27 percent. The survey found that the churn rate has been increasing over time.

And all this moving is expensive. According to IFMA, the average move in the government cost $1,340. The cost of a move depends on the extent to which the facility must be modified to accommodate the changes. IFMA found that when new walls, new or additional wiring, new telecommunications systems, or other construction was needed to complete the move, the average cost in a government setting was $3,640. However, if no furniture is moved, no wiring or telecommunication system changes are required, and only files and supplies are moved, the average cost dropped to $166.

The raised-floor system significantly reduces hoth churn costs and renovation time. No ductwork revisions or other complex construction is needed to alter workstation or work-area configurations. The access-floor system, together with floor diffusers, allows modifications to the layout of the space to be completed with very little lost work time. The cost of a move in a building with a raised floor and movable partitions would be closer to $166 than to $3,640.

What would a high-performance green building with a raised floor have meant for the Carson Building? With an annual churn rate of 25 percent, the reconfiguration of 375 workstations annually at a cost of $2,500 per reconfiguration totaled $937,500. If a raised floor would have been used, that cost would have been $93,750 – an $800,000 savings. What’s more, there would likely have been energy costs savings and gains in IAQ and occupant satisfaction.

Churn cost savings also would have accrued at a rate of greater than 2 percent of its constructed cost per year. Presented in another way, had the Carson Building been designed and constructed as a high-performance green building with a raised floor, it would have saved about $7.6 million in churn costs since its occupancy in 1993. That’s a lot of green.

James S. Toothaker is a green building consultant and former bureau director of the Department of Environmental Protection, Commonwealth of Pennsylvania.

Copyright Trade Press Publishing Company May 2004

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