The fast pace of what has been described as the technological revolution in today’s office environment inevitably results in high personnel and equipment churn rates, which in turn demand office buildings with flexible space planning and an adaptable technical infrastructure
It is becoming increasingly difficult for conventional, centralised mechanical and electrical systems to meet the demands of management or tenants for a number of reasons, including frequent personnel restructuring, changing office tenants or multi-tenancies, and regular technological upgrading or expansion.
For a typical office building, it is estimated that 45-50% of occupants will change their location or require an upgrading of their computer and/or telecommunications connections every year. The increasing demands of the IT era have resulted in the need for every workstation to be equipped with access to computer and telecommunications power sources and networks, often creating an unsightly abundance of cables, outlets and extension cords.
The role of any building’s cabling infrastructure is to provide occupants with voice, power and data connections capable of meeting not only present requirements but also the unpredictable future equipment upgrades, expansions and innovations – and without the inconvenience and safety aspects of unplanned office space and cabling strategies.
A raised access floor provides a solution to the problem of housing the many services associated with modern communication technology. It conceals all cabling while allowing easy access for maintenance or changes. The floor voids can also be used as plenums for air distribution, making the whole installation convenient, safe and pleasant for people to work in.
It provides maximum flexibility and, therefore, the facility to design the floor layout to suit the needs of the modern office for existing and new tenants. These benefits are equally applicable for retail, exhibition and education space, computer rooms, control rooms, call centres, laboratories, clean rooms and numerous other applications that seem to appear almost daily.
Although it is a specialised sector of the industry, there are a number of companies that have been supplying and installing access flooring systems for decades, and the local commercial and other organisations have benefited, with many millions of m2 of these systems having being installed – with virtually no comebacks.
Access floor systems
The key components of a raised access floor system are pedestals, stringers and floor panels. The pedestals provide the complete vertical, adjustable supporting structure to the raised floor panels, and are normally bonded to the subfloor using an epoxy resin-based adhesive with mechanical fixing also provided if required.
The pedestal assembly provides vertical adjustment of 35mm to allow the raised floor to be installed flat and level despite any undulations in the subfloor. The pedestal head provides the panel location and also (when required) a means of fixing the panel to the pedestal head.
The stringer is a horizontal component that connects pedestals together; it connects to the pedestal head and is used to provide additional lateral support at greater floor height and/or increase the structural performance of the raised floor system.
The floor panel is the horizontal loadbearing component of a raised floor. There are two basic types of floor panel construction: steel encased woodcore, and steel/cementitious filled panels – although the latter is by far the most favoured type in South Africa.
Steel encased woodcore
This panel construction comprises a high-density particle board core that is encased in galvanised steel laminated to the particle board by a structural polyurethane or epoxy resin adhesive. This construction type is capable of providing high strength and good fire and acoustic performance.
Although used fairly extensively in the USA, this is not a popular panel in South Africa because in moist, damp or even excessively humid atmospheres the composite board is inclined to warp or expand with moisture absorption.
Also, the composite panels are commonly produced with the use of formaldehyde which means that this is exposed to the breathable air as dust when the panels need to be cut, and are thus not very environmentally friendly.
Here a structural steel shell (comprising a flat steel top and a profiled steel base welded together to form a hollow shell) is filled with a foamed, cement-based core to make a panel that gives good structural performance in conjunction with excellent fire performance.
Unlike composite panels which often require renovation or replacement, the steel/cementitious panels can be refurbished relatively easily (the cement/fly ash construction is easily cut). There are installations in South Africa that have been in service for a quarter of a century, and still seem good as new.
In certain cases the hollow unfilled steel shell will provide a floor panel that gives suitable structural performance, although its acoustic performance is limited.
Although some variations exist, access floor systems consist of modular floor panels that are typically 600mm square, mounted on pedestals secured to the structural slab.
The height of the floor panels above the slab determines the plenum depth, and installations devoted only to cable distribution could be as low as 75mm. When incorporating air distribution systems, typical plenum depths range from 200-460mm, or more – depending on the system being used and given that some systems offer floor heights of up to 1,8m.
Cables can be run in any direction within the plenum, either freely or contained within flexible conduits. At various locations the cables are accessed via openings in the floor panels, floor-mounted terminal boxes, or are integrated within modular office furniture.
In this way, access floor systems provide a multi-functional floor with access to the telecommunications and HVAC connections necessary for any workspace, without compromising the aesthetics of the finished floor, enabling a cabling and floor infrastructure to be both versatile and unobtrusive.
Regarding the floor finishes, almost every type of floorcovering has products that are specifically designed to fit the grid size of the access floor. By far the most popular for South African installations are modular backed carpet tiles for general office areas and factory-bonded, anti-static, high-pressure laminate for computer rooms.
When carpet tiles form the finished floor surface of a raised access floor system the issue of coordinating the modular sizes and grid dimensions of floor panels and carpet tiles must be addressed.
Overseas some manufacturers provide a composite unit of floor-panel-plus-carpet-tile which they say enables architects to work with only one modular dimension, as the pedestal spacing of the access flooring is a function of the floor panel size.
However, this is a not a popular practice in South Africa because when areas of the factory-bonded carpet surface finish become worn the whole panel has to be replaced or refurbished, which is both time-consuming and expensive, whereas if the floorcovering is a separate item such as pressure-sensitive carpet tiles, replacement is simple and readily available.
The majority of installations comprise floor panel and carpet components from separate manufacturers. As floor panels are typically 600mm square, carpet tiles are available to fit this panel size, but in South Africa the preference is for standard 500mm x 500mm pressure-sensitive carpet tiles to be used, laid ‘off-grid’ which allow easy access to the panels.
Given the required plenum height, access flooring provides an excellent means of providing office airconditioning where required in offices, or for cooling of computer equipment, and in this country up to 50% of all access floor installations contain some form of airconditioning system.
Underfloor Air Distribution (UFAD)
Underfloor air distribution (UFAD) is an air distribution strategy for providing ventilation and space conditioning in buildings as part of the design of an HVAC system, using the plenum beneath a raised access floor to provide conditioned air through diffusers directly to the occupied zone.
The plenum height will vary, depending on the type of system being used.
UFAD is frequently used in office buildings, particularly high-churn and open-plan offices where raised floors are desirable for cable management. UFAD is also common in command centres, IT data centres and computer rooms which have large cooling loads from electronic equipment and requirements for routing power and data cables.
Specially designed floor diffusers are used as the supply outlets. The most common UFAD configuration consists of a central air-handling unit delivering air through a pressurised plenum and into the space through floor diffusers. An alternative would be to use underfloor ducting.
Many factors, including the ceiling height, diffuser characteristics, number of diffusers, supply air temperature, total flow rate, cooling load and conditioning mode affect the efficacy of a UFAD system.
To summarise, raised access floors offer a cost-effective means of addressing the key factors of modern workplaces in providing an infrastructure flexible enough to meet high churn rates in multi-tenant, multi-technology environments where the pace of future expansion is guaranteed, yet the nature of the expansion is unpredictable.
When properly coordinated and incorporated into decisions at the design, construction and occupancy stages, integrating cable management and air distribution services within the plenum of a raised access floor can increase the potential versatility of a workplace; and the ability to meet occupant preferences quickly also contributes to a more dynamic work environment.
In South Africa all the major concerns such as the banks, Vodacom, MTN, Telkom and others have used access flooring in their offices for years, usually with a plenum height of one metre to accommodate all the required services.
Access flooring is so convenient, ensuring that the office never becomes out of date. Developers and speculative building contractors have realised that by including access flooring in the design – despite the cost required in providing the extra height of the building – the building is made more versatile and attractive to purchasers or tenants, the latter able to be charged at a higher rate for the benefits the system provides.
Acknowledgement and thanks are given to the following for information obtained for the compilation of this article: Clint Hastings of Peter Bates Flooring, www.peterbates.co.za; www.cbe.berkeley.edu; www.solidfeel.com; www.batesaccessflooring.co.za