A REVIEW ON THE USAGE OF SUSPENDED CEILING IN PROVIDING BUILDING SERVICES INSTALLATION IN COMMERCIAL BUILDINGS

By : NUR AZFAHANI AHMAD, Building Surveying Department, FSPU, UiTM.



Abstract

In recent years, many commercial buildings are fully-equipped with services installation. A modern building is expected to be a source of energy appliances which provide means for communication, electricity, telecommunication, networking, lighting and many more whilst providing facilities for visual and acoustic comfort. Space will always be required within the building in which to accommodate these building services. In these days of rapid technological changes, it is often to has a ceiling in offices into which the services can be installed. This ceiling is recognised as a suspended ceiling.

It is important to analyse the effectiveness of suspended ceiling in providing means of access and spaces for building services components in terms of installation cost, type of services and maintenance works application. This is necessary to get in-depth data on the most economic and effective option in providing spaces for services installation. A proper consideration should be given in selecting suspended ceiling, because a wrong choice can raised the installation costs of building services between 50% or up to 75% of the total construction cost. Commercial buildings requires a vast range of services and it is important for designers and engineers to design proper spaces; which is suspended ceiling to accommodate these needs. Their decision will contributes to the quality and effectiveness of this element in distributing services to the entire building.

Keywords: Suspended Ceiling, Building Services, Services Installation, Maintenance

Introduction

From the early era of construction, a building was significant to give a reliable place of social and functional identity whilst creating the humanised space to carry out daily tasks and functions in comfort. A building must satisfy three conditions, which are the needs for commodity (comfortable environment conditions), firmness (stability and safety), and delight (aesthetical and psychological appeal) (Wooten, H, 1964).

Meanwhile, Roger Greeno (1997) reports that a modern building is expected to be a source of energy appliances which provide means for communication and electricity whilst providing facilities for visual and acoustic comfort. According to Franz, H and Sontag (1974), with increasing mechanisation of modern offices, more and more attention has to be paid to the proper accomodation of electric cables and wires and their accessibility at all times. In office buildings, it should be possible to install a good deal of additional electrical services at a later date. With the increasingly extensive use of computer in the offices, more data terminals are being provided, requiring cables for their connection to the data communications system.

All these criteria and performance requirements can be carried out by innovation of internal construction element that are recognised as the suspended ceiling. During the late 1960s, suspended ceiling has been developed to support building’s performance requirements which consists of commodity, firmness and delight aspect (Hale, G, 1972). By the early 1980s, the Construction Industry and Research Association (CIRIA) recognised that this internal element can facilitate more, including visual and acoustic comfort.

In these days of rapid technological changes, it is often necessary to have a ceiling in offices into which the services can be installed, and then changed without the complete dislocation of the normal use of the building. The suspended ceiling is designated to provide means of access for the purpose of the services installation, including electrical fittings and computer networking cables (Chudley,1999). Greeno (2001) reports that to meet the requirements for facilitating building services installation in the building, there are characteristics which suspended ceiling should have and these are stated as below: -

(i) Easy to construct, repair, maintain and clean.

(ii) Provide adequate means of access for maintenance of suspension system, to conceal services and light fittings.

(iii) Provide sound insulation and absorption.

(iv) Provide fire protection especially to structural steel beams that supports concrete floors.

(v) Conform to requirements of Building Regulations especially the restriction of spread of flame over surfaces of ceilings.

What is Suspended Ceiling?

BS 6100: part 1 (1984) defines suspended ceiling as ‘a ceiling hung at a distance from the floor or from the roof above and not bearing on the walls’. Ambrose (1991) defines suspended ceiling as a ‘separate ceiling structure that hung from the overhead structure, deriving support from it but not necessarily reflecting its profile or detail’. This is done to create needed space for services element such as lighting, HVAC service, fire sprinklers, and smoke detectors. It also can provide different form of ceiling and aesthetic functions.

The increasings demand for sophisticate services provision in buildings has resulted in an increased use of suspended ceiling to house all building services. Burberry (1997) states that, the design decisions of suspended ceiling were influenced by balancing required performance against acceptable cost. Designers, owners and users of buildings have a responsibility not only to design well but also to adopt responsible standards towards building services installation. The economical layout and careful analysis of loads to be met are critical to the efficiency of economy and installation at suspended ceiling.

PERFORMANCE REQUIREMENTS OF SUSPENDED CEILING

There are several British Standard references that can describe the performance requirements for suspended ceiling in detail. It is essential to overview the performance requirements of suspended ceiling and use the British Standard references as a guide and benchmark. It is also important to consider the ceiling in relation to partitioning system and raised floor system especially when the building consist maximum usage of mechanical services that may be used by the building. Louise Holgate (1987) lists the performance requirements for suspended ceiling as belows:-

(i) Accessibility – It is important to consider the provision of access point which often associated with future need to change lighting or partitions. Access points may present fire test problems. Checks on air-tightness may be needed. Adequate space allowance must be provided within this void for installation as well maintenance. The most noticeable development over the past years is the easiest means of access, which is modular panel, which can be removed over the whole area of the ceiling.

(ii) Fire Precautions – Any fire resistance of a suspended ceiling can be added to that of the floor above. Experience of real fires has shown that dry suspended ceilings have to be carefully designed, installed and maintained. The more complex the ceiling the less likely it is contribute to fire resistance. We should consider fire precautions into two aspects; fire resistance of construction and surface spread of flame characteristics. Fire breaks will be required within the suspended ceiling if fire compartment walls stop at ceiling. If access for servicing is to be provided, care must be taken not to affect the fire resistance. Figure 1 shows the basic approach to avoid fire from spreading to the other compartment of cavity in the building.

(iii) Appearance – Suspended ceiling is essential in providing concealment for services pipes or for visual and aesthetic purposes. A lowered ceiling can be applied to increase the quality of interior spaces and improve its height proportion. The setting out of modular ceilings, the junction detail between ceiling and wall, and the quality and accuracy of workmanship should be put in consideration during its installation.

(iv) Durability and Maintenance Aspects – Suspended Ceilings need to be design properly before its installation, to extend its working-life durability. The maintenances need to be carried out regularly to avoid any emergencies or complaints from client. Building maintenance manuals should include very detail information about cleaning and maintenance methods that suitable for each types of ceiling systems.

(v) Sound ControlA measure of sound absorption is shown in the sound absorption coefficient; the higher the coefficient, the better the absorption. Suspended ceilings can contribute to the sound resistance and absorb sound thus correct the acoustics problem. Absorption material that suitable for sound control is mineral fibre-tiles. Suspended ceilings are normally used to provide the correct acoustics requirements in a room. The machinery used in an open-plan office; such as computers and printers, needs acoustic absorbent material which can only be suitably placed at ceiling level. Wall finishes, partitions, carpet and furniture need to be taken into account when considering the acoustics of the space (Holgate, L, 1987). Table 1 shows the types of acoustic absorbent for suspended ceiling.

Table 1: Types of acoustic absorbent for suspended ceiling

Types

Characteristics

Resonant Panels

To absorb sound near their resonance frequency (50-500 Hz). The examples of material are plywood and hardboard.

Porous Surface Panels

To absorb frequencies of 500 Hz – 4000 Hz. The example of material is mineral fibre.

Semi-Perforate and Perforated Composite Panels

It has a porous material surface material which is textured, perforated or drilled to improve acoustic efficiency and appearance. The example of material is Gypsum Plasterboard.

Perforated Panels

These panels are back with independent acoustic absorbent materials used over an airspace combine the advantages of porous absorbents with resonant panels.

Sources: Blanc, A (1994), Mitchell’s: Internal Components, Longman Scientific, Essex, pg 45.

THE COMMON TYPES OF SUSPENDED CEILING USED IN COMMERCIAL BUILDINGS

In providing building services installation in to commercial buildings, suspended ceilings are categorised by method of construction and type of form. There are several types of suspended ceiling which are widely used in providing spaces for services. Each one of these types has its own capability and quality.

One of the most familiar and economical option for suspended ceiling is a Jointless Ceiling Systems. This type of suspended ceiling have 2-4 hours fire resistance with a class 0 surface spread of flame specification. Light fittings, ventilation ducts, electrical cables and many more services can be easily accommodated in the suspended ceiling if there are proper plan of design during the early stage of construction.

This ceiling is suitable to apply to any shape of the building and easily accommodate to any size of light fittings. There is absorbent quilt for sound absorption purpose. Usually, the jointless ceiling with plasterboard will be screwed to metal framework.

There is also another option of suspended ceiling, which known as Frame and Tile Systems. It consists of tiles or planks laid into a framework suspended from the structural ceiling above. The framework may be exposed, concealed or semi-concealed. Materials and finishes for tiles and panels can be various, including mineral fibre tiles, metal trays and open grid tiles.

Mineral fibre tiles need to have protective edges because this material is vulnerable and easily damaged.

Table 2 The advantages and disadvantages of frame and tile systems.

Criteria

Advantages

Disadvantages

Access

All panels are easily removed thus provide easy access for maintenance. Good access to the ceiling void at the head of partitions.

For concealed panel framework, it will makes access difficult compared to exposed panel framework.

Sound

Good for sound absorption.

Low in sound insulation because of the lightness of the ceilings.

Lighting

For Concealed System-Provide a good surface and good reflective finish.

Provide Exposed System-Provide Poor surface For Uplighters.

Installation

Easy connections to adjacent surfaces because tiles can be cut to fit.

Materials can be easily damaged during services installation

Fire

-

Have large number of joints thus reduce fire resistant capability.

Source: Holgate, Louis (1987), Design Data, AJ Focus, Architecture’s Journal, London


Integrated Services Frame and Tile System ceiling is the new breed of frame and tile system. It has a much larger grid layout than the other ceiling systems. Parts or the entire supporting frame should be constructed with larger metal sections. The frame can support air intakes or extracts for air-conditioning system, light fittings, alarm system, audio and speaker or fire protection system to suit within the module.

In the mid 90s, the new era of building designers have prefer a new ceiling system that is more artistic, hip and stylish due to represents a serious attempt to generate a passively-ventilated building without losing architectural repose. Louvre/open grid system is the new option of ceiling system that consists of a series of louver panels made from timber or metal. These types of ceiling effectively gives support within as a suspended ceiling and give a visual cut-off when seen from below, although most of the area is open. The grid or louvers area generally of timber or metal suspended from the structural ceiling above.

This type of ceiling used in areas where there are a large number of services. It can conceal service pipes and ducting. The means of access is acceptable and easy. In term of sound, it will provide poor sound absorption because of the louvers construction. It will provide poor fire resistance although sprinklers have been connected. In term of services installation, a variety of light fittings can be fit into the cell and open grids can be lit to give different effect for the light. For areas with different shapes and sloping ceilings, the louvers and grids are difficult to fit.

SERVICES ACCOMMODATION IN SUSPENDED CEILING

In most multi-storey commercial buildings, suspended ceilings fulfill its purposes of providing services, distribution space, conceal both services and structure, protect structure against fire and also give acceptable decoration internal finish. Azfahani, N (2004) reports that one of the commercial buildings in Scotland used a suspended white metal vaulted panel ceiling that serves to reflect the light from luminaries suspended below and also to conceal the return air duct and to carry sprinkler heads, electrical ducting, and communication cablings.

In general offices building throughout the nation, the users tend to operate mostly as individuals, thus each work station have one electrical supply outlet, telephone cable supply outlet and computer supply outlet from the multi-sided power post that came from suspended ceiling. The arrangement is designed to maximise flexibility so computers and furniture can relocated easily. In each work station, the users need to be encouraged to use their power post appropriately.

§ Heating, Ventilating, Air-Conditioning and Cooling Systems (HVAC)

The interior of buildings are ventilated in order to provide comfort environmental condition. In the UK, the Chartered Institution of Building Services Engineers (CIBSE) guide suggests that the quantity of fresh air needed can vary from 8 litres per person/second in fairly smoke free environments. Whilst in the Malaysia, the Uniform Building By-Laws (1984), the fresh air needed in rooms are 28 nos of air changes rate/hour. Thus, there are need to provide natural air inlet, natural air outlet and mechanical inlet and outlet as well (CIBSE, Guide B2, 1998). Heating, ventilating, cooling and general treatment of the building’s interior thermal and atmospheric condition is a multidimensioned task. Air conditioning in HVAC term can be defined as the cooling of interior air, which include filtering out of dust and odours, freshening with outdoor air, adjustment of temperature and relative humidity (James E. Ambrose, 1991).

HVAC systems generally include the heat-generating system, a cooling system, an air-handling system, a control system for hand adjusting and automatic monitoring of the system operation. When designing the heating system for a building in the UK, the fundamental considerations are the internal room temperature to be maintained. The temperature of the flow in low-pressure hot water heating systems is 80ºC with a 10-20ºC drop. By assessing the temperatures needed at the heat emitter in each room and the drop in flow temperature, the size of the distribution pipework can be assessed.

Whilst in Malaysia and other tropical countries, designing the air-conditioning system for a building requires a balance temperature within the comfort natural environment outside in a range 17-22ºC. A wide range of air-conditioning system can be installed to supply fresh air and extract heat. A centralised unit of air-conditioning system is essential to allocate into a suspended ceiling in providing thermal comfort to the occupants. The suspended ceiling helps to provide space for fresh air distribution from the central air handling unit.

§ Electrical Installations

Installations using electricity for power supply, lighting, environmental control, communications, security and computing are now essential provisions in all buildings. In some large commercial buildings, the pattern of layout and use made of electronic equipment has connected for very large open spaces with cable access to every point. Christopher (1988) stated that for office buildings, the overall power consumptions will require the use of three-phase supply. There are many user outlets to serve, especially in multi-storey structures, there will be items in common use which will require a power supply, particularly the heating boilers and air conditioning.

A three-phase busbar panel can present a means of easy connection for single-phases rises to the various level in the building. A final sub-circuit will extend into the user’s areas via a consumer control board where the isolation switch and fuses are located. There are a three-phase supply busbar throughout the full height of the building and tap-off single-phase supplies as required to each floor level (Howard, C. A, 1988).

A typical three-phase busbar supply system consists of four copper rods threaded through rigid insulators to space the conductors apart and a cover ing of trunking to protect against electrocution.

§ Fire Fighting Installations

Fire fighting installations that usually installed in suspended ceiling are categorised under active fire control, and this is included sprinkler systems, smoke and heat detectors, fire detectors and fire alarms. As an office with full of technology components, th e suspended ceiling system need to be provided with fire protection system that link directly to the nearest fire station. In the event of fire, direct signal will be transferred to the fire station, within 30-60 seconds. There are sprinkler heads, smoke detectors and heat detectors in range of 12 square meters for each components. Water sprinklers will provide an automatic spray out-and-out to the area of fire. The water supply for sprinklers are gain from the suction tank that supplied from a water main. For the office areas that have floor area of 1500 square meters, the number for sprinkler heads are 125 sprinkler heads. All fire protection system in the building is control by the system control unit in the control room.

For sprinkler, it consists of a grid of water pipes under the ceiling with delivery heads. When the temperature rises, the liquid will expands, breaking the sprinkler’s bulb that is preventing the water passing. A jet of water then impinges on the shaped plate, delivering a spray of water over10 m2 area. For smoke and heat detectors, they have sensors that can close an electrical circuit to provide alarm. They are widely used and supply with battery backup (Burberry, P 1997). In larger buildings, it is necessary to have an alarm system for any fire detector to activate audible alarm throughout the building. Manual alarm and automatic detectors should be incorporated into the system and operate on a phased basis to avoid congestion in the escape route.

§ Signal and Communication Systems

Every commercial buildings these days has communication systems fully operated for the building. In many buildings, there are close circuit television (CCTV), public address, computer networks or intercom systems (Harold, K and Derek, O, 1985). Each of these systems is typically operated with separate wired, low voltage and direct-current electrical system.

§ Lighting System

Individual lighting fixtures, both permanently installed and movable, abound in great variety. There are pendant types, surface mounted types, semirecessed, recessed any many more. Lighting require considerable structural support at suspended ceiling, but small fixtures are often structurally supported by the connecting boxes installed with wiring. The aim of the lighting control is to minimise the energy consumption associated with lighting whilst maintaining a comfortable light level. Usually, in each commercial buildings, there will be one device provided to control of the fittings, allowing the lamps to be switched depending on daylight penetration. There are individual controller within the office spaces. The benefit of this lighting system is there are no need to install switch drop in the wiring circuits which not only saves on the installation costs but also increases the flexibility to mix with other services in the suspended ceiling. There are Tungsten Halogen type of lamp, Fluorescent Lamp, Compact Fluorescent lamp and Sodium Lamps (Peter, B, 1997). Figure 10 (a)&(b) shows the principle of glare classification.

SPACE AND PROTECTION REQUIREMENTS

Space and the cost of providing space for building services distribution is usually at a highest priority. Considerable care is needed for building services in providing adequate space for the safe and efficient maintenance of the installations. The needs for access is also important and need to be restricted for maintenance purpose. There is guide for space requirement provided in BS 8313 (1997). This code provides recommendations on space provisions for safe access, installation and maintenance of service ducts.

§ Space Allowances For Ducts

Table 2 Specific Requirements For Ducting Space.

Space for air ducts

Space for supply and return air ducts can be estimated by dividing air volume flow rate by a velocity 0f 4 m/s.

Vertical ducts for piped and electrical services

The installation space for each floor is between 1m2 – 2m2 for each 5000m3 of building volume.

Space for additions and alterations

Provide 10% - 15% extra space for future additions and alterations.

Depth of ceiling voids

Ceiling voids should have minimum depth of 500mm free of structural member. Each service duct should serve a maximum area of 1000 m2.

§ Installation

To avoid difficulties during the services installation; the minimum distance between the outer space of any service and any obstruction should be 25mm for pipes and cables, 75mm for union joints and 100mm for ducts. The suitability of the building structure from which the ceiling is to be suspended should be verified. Then, top fixings can be installed. Hangers for ceiling should be vertical and should not press against insulation covering ducts or pipes. Wire hangers should be carefully straightened and tensioned before use. Installation should be considered whether the the grids are exposed or concealed. For service outlets, the air terminal devices or similar equipment should be incorporated in the ceiling (British Standard; BS 8313: 1997).

§ Maintenance

i. For maintenance purposes, sufficient space should be provided for the operation, inspection and repair of valves, dampers, cleaning points, expansion joints and other fittings, and the cleaning and painting of the inside of the duct and the services within it. Additional spacing exceeding 250mm is needed for access of tools and work on pipes and ducts.

ii. Services should be arranged so that it is possible to remove one without disturbing the others.

iii. Careful consideration should be taken to the demolition of the duct and disruption of other services will be acceptable when a service is to be maintained.

iv. The manufacturer should provide advice on the care and maintenance of ceiling components especially at access locations. If replacement of lamp is needed, the ceiling should be considered clean afterwards.

v. For the decoration work, manufacturer should provide recommendations on the best method for redecoration.

vi. For the surface spread of flame characteristics of the infill units, care will be needed to make sure that maintenance works does not change it. Paint of non-bridging consistency should be applied to prevent bridging the joints between units or filling in the face of units.

vii. In term of extensive removal and replacement works, it is wise to appoint suspended ceiling specialist to do it (British Standard; BS 8290-3:1991).

§ Access

It is important that access is provided to ducts, large enough to be entered. Access is needed to achieve good maintenance, operation and installation of the services. BS 8313 (1997) stated that there are minimum sizes for horizontal ducts and vertical ducts that should be followed. For horizontal ducts, it is 600mm x 900mm wide/long or 600mm wide x 600mm high. For vertical ducts, it is 600mm wide x 1800mm high or 600mm wide x 1400mm high. If it necessary to maintain and the enter the duct, the maintenance working space should be less than 700mm (width), 1000mm (height) with volume 1.4 m3 for horizontal ducts or 600mm (width), 750mm (depth) with volume 0.9 m3. There are also need to consider access level based on maintenance frequency especially on electrical services (CIBSE guide, 1996).

There are 3 types of access level, which are :-

§ Access for Frequent Maintenance – All services equipment should have permanent clear and immediate access with adequate space provision to settle the task.

§ Access for Maintenance on an Occasional Frequency – Access can be achieved by removal of clearly marked panels in suspended ceilings. It is good to have quick-release fasteners to screwed fixings.

§ Access for Emergency Repair and Replacement – If is essential to replace major plant or equipment, the arrangement of permanent clear access for emergency repair need to be informed and agreed with the client. Sufficient standby design and work layout should be specified.

CONCLUSIONS

Highly serviced buildings such as commercial or office buildings, can raise the installation costs of building services by up to 50%-75% of the total construction cost. Whilst, services elements can also take up 15% of a building’s volume (Fred Hall, 2003). This shows that building services are very important to commercial buildings and must not be neglected. It is important to accept and understand the increased need for building services element in the building. One of the major factor that will be needed to consider in providing spaces for building services installation is the choice of suspended ceiling. The relationship of this component towards buildings services installation, contribute to the quality and effectiveness of the building in distributing services to the entire building. Even though there is also raised floor that can provide spaces for building services installation, it is essential to consider the most economic and effective option to distribute services.

Judy Shaw (2002) reported that the demand for raised floor has remained static for the past 2 years. It is believed that the cleverer information and technology installation could see most of the services run in the suspended ceiling. Simon Ridyard (2001) believed that raised floor is not economical because the value of spending on floor is a lot more higher, while the occupants may not benefit the floor directly. The main point is raised floor is only able to lay the power cables, voice and data communications which will only serve ¼ of services element compared to suspended ceiling. It proves that suspended ceiling is the most economic and wise option in providing space for building services installation. This is because, suspended ceiling has provides 60% of building services installation in the commercial buildings and raised floor only provides 40% of building services installation. Today, the structure of suspended ceiling can integrates with the new technology of Building Management System (BMS) and at the same time, remain to be cheaper than raised floor.

A good suspended ceiling should obtain all performance requirements that are essential and these are best followed using BSI Standard Guide. High consideration should be taken on the costs of the construction, the maintenance and the access to install the services.

REFERENCES

Ambrose, James (1991), Building Construction - Interior Systems, Van Nostrand Reinhold, New York.

Ambrose, James E. (1992), Building Construction - Service Systems, Van Nostrand Reinhold, New York.

Barron, Sam (2004), Contruction Technology Handout Notes, Heriot Watt University, Edinburgh

Blanc, Alan (1994), Mitchell’s: Internal Components, Longman Scientific and Technical, Essex.

BS 6100: 1984, Glossary of Building and Civil Engineering Terms, BSI, London.

BS 8290-3:1991, Suspended Ceilings (Part 3)-Code of Practice For Installation And Maintenance, BSI, London

BS 8313: 1997, Accomodation of Building Services in Ducts, BSI, London

Burberry, Peter (1997), Mitchell’s: Environment and Services (8th Edition), Addison Wesley Longman Limited, Essex.

Calvert, Bailey and Coles (2000), Introduction to Building Management (6th Edition), Butterworth Heinemann, Oxford.

Chartered Institution of Building Services Engineering (CIBSE), IHVE Guide B2, Air Conditioning Requirements.

Davies, Hywel (2001), Building Life Plan-Building Services Component Life Manual, Building Performance Group Limited, Blackwell Science, United Kingdom

Davis Langdon and Everest (2004), Spon’s Architects’ and Builders’ Price Book (129th Edition), Spon Press Group, London

Fellow, Richard and Liu, Anita (1997), Research Methods For Construction, The Blackwell Science, London.

Hall, Fred and Greeno, Roger (2003), Building Services Handbook (Second Edition), Butterworth-Heinemann, Oxford.

Haniff, Amos (2001), Standard Life House-Asset Maintenance Management Case Study Disk, Building Case Study, Department of Building Engineering and Surveying, Heriot-Watt University, Edinburgh

Hart, Franz, Henn, Walter and Sontag, H (1978), Multi-Storey Buildings in Steel (Second Edition), William Collins Sons & Co. Ltd., Germany.

Harvey, Nigel (2001), A Practical Guide-Life Expectancy of Building Components, Building Maintenance Information, Royal Institution of Chartered Surveyors, London

Holgate, Louis (1987), AJ Focus: Design Data, Architecture’s Journal Magazine, London

Howard, Christopher A. (1988), An Introduction To Building Services, Macmillan Education Ltd, Hampshire.

Judy, Shaw and Ridyard, Simon (2001), AJ Focus :Theme-Ceilings, Partitions and Raised Floors, Architecture’s Journal Magazine, London

King, Harold and Osbourn, Derek (1985), Mitchell’s Building: Components (Reprinted Edition), BT Batsford Limited, Essex, England.

Ministry of Defence (July, 1996), Defence Works Functional Standard: Design and Maintenance Guide 08 - Space Requirements For Plant Access, Operation And Maintenance, Defence Estate Organisation, Norwich.

Mott Green and Wall (2004), Spon’s Mechanical and Electrical Services Price Book (35th Edition), Spon Press Group, London

Pearman, Hugh (1999), Sweet Clarity-Building For BT, The Architects’ Journal, p. 33

PSA Specialist Services (1992), Performance Specification (Raised Access Floor), The Property Services Agency (PSA), London

Ridyard, Simon (2001), AJ Focus: Theme-Ceilings, Partitions and Raised Floors, Architecture’s Journal Magazine, London

No comments: