The Great Debate: Raised Floor vs. Slab Data Centers

Paper or plastic? Coke or Pepsi? Raised floor or slab floor?


Some debates never produce a clear winner, and in the data center world, the topic of raised floor versus slab floor construction falls into that category.  Although 20 years ago, the discussion was barely audible— nearly all data centers were built using raised floors — over the past decade, the theme has been at the forefront of many heated discussions among data center professionals.


While an endless slew of studies and white papers exist to support each side, the bottom line is this:  the best design for a data center is one that is optimally aligned with the operational and business objectives identified by the company.  Just like a preferred taste for either Coke or Pepsi, it comes down to the best individual fit.


One of the primary considerations is whether your data center is being built for a specific purpose by a single owner or tenant, or if it will serve as a multi-tenant colocation facility required to meet a broad spectrum of needs.


For multi-tenant facilities that must take into account future flexibility, the raised floor approach offers an advantage. That’s because the accessible raised floor plenum facilitates easy additions to cooling or electrical infrastructure — it’s much simpler to run new conduits or piping under a raised floor than it is to run them overhead.  The flexibility to install future services to cooling equipment such as door coolers, in-row cooling units, or heat transfer media direct to servers is important for some facilities.


On the other hand, when it comes to equipment installation and movement, as well as overall maintenance costs, the slab floor is the front runner. Concerns with point loading or moving loads that are associated with raised floor systems are not an issue with a slab floor. Additionally, the cost for maintenance runs lower.


Cooling efficiency is one of the factors that virtually every data center operator is seeking in a base design, but a variety of analyses have concluded that neither option offers a significant advantage. A pressurized raised floor system delivering cooling air through perforated floor tiles consumes about the same amount of energy as cool air being pushed through overhead ducts and diffusers. From a layout flexibility perspective, a raised floor provides the benefit of being able to easily rearrange perforated tiles.  Yet overhead cooling tends to produce fewer issues with air leakage or air bypass. And finally, when it comes to cooling efficiency, system air balancing tends to be a little more difficult in a raised floor environment.


Most construction cost comparisons fail to produce a clear victor, as well.  The various component costs associated with each approach yield a similar cost per square foot of data center area, according to most studies.


For regions prone to earthquakes, seismic performance is also a consideration, with the slab floor getting the nod. Not only is it a less costly option, but equipment anchoring is easier and the added lateral bracing and reinforcement associated with a raised floor system are not issues. 


Finally, market demand may also play a role in data center design. In some regions of the world, the market simply expects data center facilities to have raised floor.


So the next time the great debate arises over slab versus raised floor, there’s no need to join in the dispute. Instead, just sit back and relax, and raise your glass of Coke. Or Pepsi.



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