Raised access floors

There are numerous different types of raised access floors ranging from types that use bricks held in a plastic tray to conventional metal pedestals with metal encased chipboard or gypsum cored tiles (see next page).

In the UK, the main standard for raised access floors was at one time the PSA MOB standard which set out 4 levels of duty. For most speculative office buildings, a medium grade floor was usually specified. More recently, the specifier also has the choice of tiles to BS EN 12825, which theoretically at least expands the range of performance to numerous possible combinations (see Specifications).

For most fully accessible floor systems, the easy removal of individual tiles is critical. The tiles should be capable of lifting, rotation through 90° and reinsertion without difficulty.

The floor should not rely upon the perimeter walls or partitions to provide lateral stability; it should be capable of supporting itself without additional lateral restraint (other than within the floor system). For this reason pedestals are normally fixed down, either mechanically or with adhesive (sometimes both).

Check adhesive-fixed pedestals to ensure that they are properly bonded or that the bond strength is not greater than the strength of the floor screed. (Lightweight floors, such as lytag concrete, have a low strength and often fail in preference to the adhesive.)

Cut tiles need proper support, so perimeter details need additional scrutiny to ensure that proper support (additional pedestals) has been fitted and that the tiles are tight and secure. Cut tiles should not be less than 150mm wide to avoid fixing difficulties, and should generally be mechanically fixed rather than simply retained under gravity.

Loose tiles at door threshold positions could be particularly dangerous and so perimeter stringers should also be placed in these positions.

The serviceability of raised access floors can be reduced by factors such as deflection in the structure, pedestal movement (during fit-out or maintenance operations), damage to tiles during handling and/or excess tackifier adhesive working its way between tile joints (see Critical points).

In data centres, the formation of zinc whiskers (microscopic filaments of zinc) on galvanised steel floor components can cause serious problems to sensitive electronic equipment if they are disturbed and enter air circulation.