# 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.

## 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

| Parameter | Typical position | Why |
| --- | --- | --- |
| Void depth | 100-150mm for power/data | Deeper if the void is also an air plenum |
| Panel core | Calcium sulphate or steel-encapsulated chipboard | Calcium sulphate is denser, better acoustically, non-combustible |
| Panel size | 600 × 600mm | Matches ceiling grid and workstation planning |
| Loading grade | Medium general, heavy at server and storage | Concentrated load, not just distributed |
| Pedestal | Adjustable, bonded to slab | Bond quality determines whether the floor rocks |
| Finish | Carpet tile, vinyl or bare with loose lay | Carpet tile is standard for offices |
| Fire stopping | At every shaft and compartment line | The 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**.

## Frequently asked questions

### What void depth does an office actually need?

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.

### What panel loading should be specified?

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.

### Why do raised floors rock or squeak?

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.

## Sources

- [IS 875 (Part 2)](https://standards.bis.gov.in/website/published-standards/department-wise) — Imposed loads
- [NBC 2016, Part 4](https://www.bis.gov.in/standards/national-building-code/?lang=en) — Fire and life safety

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Source: https://hagerstone.com/glossary/raised-access-floor