Raised Access Floor: The Void That Runs the Office

A raised access floor is a grid of removable panels sitting on adjustable pedestals above the structural slab, creating a shallow service void for power, data and sometimes air — so cabling can be rerouted later by lifting a tile rather than opening a ceiling.

By Dhruv Agarwal · · 2 min read

Why it matters on a fit-out project

The raised floor is invisible in every photograph of a finished office and determines much of how the office actually works. It sets where a desk can have power, how easily a layout can change in three years, and — because it eats slab-to-slab height — how tall the finished space feels.

It is also one of the earliest decisions. Void depth has to be fixed before the ceiling design is settled, because the two are competing for the same dimension.

How it is specified in practice

ParameterTypical positionWhy
Void depth100-150mm for power/dataDeeper if the void is also an air plenum
Panel coreCalcium sulphate or steel-encapsulated chipboardCalcium sulphate is denser, better acoustically, non-combustible
Panel size600 × 600mmMatches ceiling grid and workstation planning
Loading gradeMedium general, heavy at server and storageConcentrated load, not just distributed
PedestalAdjustable, bonded to slabBond quality determines whether the floor rocks
FinishCarpet tile, vinyl or bare with loose layCarpet tile is standard for offices
Fire stoppingAt every shaft and compartment lineThe void is continuous and crosses compartments

Common mistakes

  • Deciding void depth after the ceiling. Floor void, structural zone, service zone and ceiling void all share the slab-to-slab dimension. Resolve them together at concept, not sequentially.
  • Specifying one panel grade everywhere. Server rooms and storage need a heavier grade, and the fit-out route itself takes loads the finished office never will.
  • Ignoring the slab surface. Pedestals bond to the slab. Dusty, uneven or laitance-covered concrete produces a floor that rocks from day one.
  • Forgetting fire stopping in the void. It is a continuous horizontal cavity and must be stopped where it crosses compartment lines under NBC 2016 Part 4.
  • Cutting tiles badly at the perimeter. Perimeter cuts are where a floor looks cheap and where edge support most often gets missed.

Standards referenced

Imposed floor loading is derived from IS 875 (Part 2). Compartmentation and fire stopping through the floor void fall under NBC 2016, Part 4.

Standards referenced

Frequently asked

For power and data only, 100-150mm is usually workable. Where the void is also used for air supply in an underfloor air distribution system, it needs considerably more — commonly 300mm or above — because the void becomes a plenum and needs free cross-sectional area. Decide this before the slab-to-slab height is committed, because it competes directly with ceiling void and finished ceiling height.

General office areas are normally specified around a medium-grade panel. The areas that actually matter are the exceptions — server rooms, filing, heavy storage and any route a pallet truck will use during fit-out. Those need a heavy grade, and they need to be identified on a drawing before ordering, not discovered when a panel cracks.

Almost always pedestal installation. Pedestals must be bonded to a clean, level, laitance-free slab and set to a consistent height, and the grid must be square. A rocking tile is a levelling or adhesion problem, and a squeak is usually metal-to-metal contact from a missing or perished gasket strip on the pedestal head.

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