Steve Hambruch, Data Center Architect at Data Center Resources (, says:

Are raised floors a way to save costs?
This approach has the ability to save considerable CapEx and OpEx dollars. First, the raised floor itself is a considerable expense in new build-outs, and the efficiency gains afforded by row based cooling or ducted air side/water side economizers can dramatically reduce operational costs.

What are the advantages and disadvantages?

Advantages: In general, much higher heat densities can be supported for typical rack mount server equipment as opposed to a traditional raised floor. These environments also typically present lower construction costs, operational costs and faster ROI than traditional raised floor environments. They also encourage more effective cable management.
Disadvantages: It is generally not as effective for rooms that support heterogeneous platforms including large storage appliances, mainframe equipment, and other equipment that is designed to work in a raised floor environment. A major renovation project is typically required to convert an existing room. In some high density environments, studies have shown raised floor plenums actually outperform non-plenum overhead cooling due to better overall distribution of the cooled air.

Data Center managers should pay careful attention to what types of devices the room will be expected to support over its useful life cycle. Specifically, what are the cooling characteristics of these devices? Non plenum rooms allow for very innovative row based cooling for rack mount servers that draw air from the front and exhaust it from the back. However if there will be equipment that is designed to draw air from the bottom and exhaust through the top or sides, such as mainframe equipment and most large storage appliances, special consideration would have to be given to cooling these devices in a non plenum space.

Also, it is important to note that simply removing the raised floor from the design is insufficient. It must be part of a holistic design that incorporates an optimized cooling system design, aisle containment, fire suppression, and many other factors.

What do you recommend if an IT manager is planning a data center renovation or move soon?
I recommend that they enlist the services of a qualified design consultant to help them determine the best strategy for their particular needs. There is no silver bullet in data center design. Each room is as unique as a fingerprint, and while the trend towards non-plenum rooms is evident, it does not mean that it will be the best suited solution for a specific data center.