Raised floor

[edit] Introduction

A raised floor, also known as an access floor, raised access floor or platform floor, is a floor constructed above a solid floor slab, leaving a void between the two. The void can be used to accommodate and distribute building services, including:

• Data and telecommunications cabling.
• Electrical power and control cabling.
• Water supply and drainage.
• Heating, ventilation and air conditioning (HVAC) services.
• Cabling and services for environmental controls, fire detection, fire suppression and security systems.

Raised floors first emerged in the 1960s and have become increasingly common with the growth of information and communications technology in buildings. They are particularly associated with offices, data centres, server rooms, control rooms, telecommunications facilities, laboratories and other spaces with significant requirements for building services and flexible infrastructure.

The principal advantage of a raised floor is the creation of an accessible service zone beneath the finished floor. Removable floor panels allow services to be installed, inspected, maintained and reconfigured without extensive work to the structural floor. Workstations, floor boxes and partitions can also be relocated with less disruption where the raised floor system has been designed to accommodate such changes.

[edit] Components of raised floors

A raised floor generally consists of a system of adjustable supports and removable panels. The principal components can include:

• Pedestals, which provide the adjustable vertical support structure. They may be bonded to the subfloor and adjusted to establish a level plane.
• Stringer bars, which connect pedestals to form a supporting framework. They can provide additional lateral stability, particularly where the floor void is relatively deep.
• Floor panels, which form the walking surface of the raised floor.
• Floor finishes, such as carpet tiles, which can generally be removed to provide access to the panels below.
• Floor boxes, which can be incorporated into floor panels to provide connection points for power, data, telecommunications and other services.

Raised floor systems can be gravity or loose-lay systems, in which panels rest on the pedestal heads and can be lifted to provide access to the void. Alternatively, panels can be lock-down or screw-down systems, in which they are fixed to the supporting structure to provide greater resistance to movement or unauthorised removal.

[edit] Floor panels

Floor panels are commonly modular and are often 600 mm × 600 mm. Their construction can vary according to the required structural performance, weight, fire performance, acoustic characteristics and intended use.

Common panel constructions include steel-clad panels with a chipboard or other core, steel panels filled with cementitious material, calcium sulphate panels and wood-core panels. Perforated panels can also be used where air needs to pass through the floor, for example as part of an underfloor air distribution or cooling system.

The panel construction and finish should be selected according to the anticipated loading and environmental conditions. Areas containing heavy equipment, such as data centres, may require panels with greater load-bearing capacity than general office areas.

Floor panels can receive a range of finishes, including high-pressure laminate, vinyl and carpet tiles. Bare panels can also be supplied for finishes to be applied on site. In areas containing sensitive electronic equipment, flooring with appropriate electrostatic control properties may be specified.

[edit] Floor voids and building services

The depth of the floor void varies according to the requirements of the building and the services that need to be accommodated. Very shallow systems can provide space for limited cabling, while deeper systems can accommodate larger quantities of services and, in some applications, air distribution.

The void can be used to route electrical power, data and telecommunications cabling and other building services. Where appropriate, this can reduce the need for services to be installed within walls, ceilings or other parts of the building fabric.

Where floor voids are used as plenums, they can act as ducts through which air is supplied to or extracted from occupied spaces. In such applications, the construction of the raised floor and the joints between panels may need to provide an appropriate degree of air tightness to limit pressure loss.

Perforated or grille panels can be used where air needs to pass directly from the floor void into the occupied space. The design of such systems needs to take account of the required airflow and the arrangement of the services within the void.

[edit] Uses and benefits

Raised floors are particularly useful in buildings where the location and configuration of services may need to change during the life of the building. Offices, data centres, server rooms, control rooms, telecommunications facilities, laboratories and other technical spaces can benefit from this flexibility.

The ability to lift individual floor panels provides relatively straightforward access to services below the floor. This can simplify inspection, maintenance and alteration and can reduce disruption when equipment, workstations or building layouts are changed.

The system can also provide a means of accommodating a large quantity of cabling and other services without exposing them within occupied areas. In some buildings, the underfloor void can form part of the environmental control strategy by providing a route for conditioned air.

[edit] Dimensions and structural performance

The dimensions and structural characteristics of raised floor systems vary according to their intended application. Floor panels are commonly 600 mm × 600 mm, while floor voids can range from shallow spaces of around 20 mm to systems with voids of 1,200 mm or more. Deeper systems can be produced for particular applications.

The required load-bearing capacity depends on the use of the space and the loads imposed by occupants, furniture, equipment and other installations. The design should consider both concentrated and distributed loads and the performance of the complete raised floor system rather than the panel alone.

For many years, the Property Services Agency specification MOB PF2 PS/Spu, Platform Floors (Raised Access Floors) Performance Specification, was used as a basis for the performance classification of raised floors in the UK. Its last edition was published in 1992 and classified floors into four structural categories: light, medium, heavy and extra heavy.

It was superseded in 2001 by BS EN 12825, Raised access floors, which classified raised floor systems according to characteristics including ultimate load, safety factor, deflection under working load and dimensional tolerances.

[edit] Acoustic considerations

Raised floors can provide a route for flanking sound transmission between adjacent spaces, particularly where partitions do not extend through the raised floor to the structural slab.

The acoustic performance of the system can be improved through appropriate floor panels and finishes, reduction or sealing of joints between panels and the incorporation of acoustic insulation beneath partition walls. In some situations, partitions may extend through the raised floor to the structural slab. This can improve acoustic separation but reduces the flexibility to relocate partitions in the future.

The extent of flanking transmission depends on the construction and acoustic characteristics of the complete floor and partition system. Similar considerations apply to other building voids, including ceiling voids.

[edit] Related articles on Designing Buildings

• Access floor
• Floor
• Flooring
• Types of floor
• Finished floor level
• Floating floor
• Separating floor
• Acoustic insulation
• Flanking sound
• Underfloor air distribution

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