Suspended ceilings (sometimes referred to as dropped ceilings or false ceilings) are secondary ceilings suspended from the structural floor slab above, creating a void between the underside of the floor slab and the top of the suspended ceiling.
As well as concealing underside of the floor slab, this void can provide a useful space for the distribution of heating, ventilation and air conditioning (HVAC) services and plumbing and wiring services, as well as providing a platform for the installation of speakers, light fittings, wireless antenna, cctv, fire and smoke detectors, motion detectors, sprinklers and so on. The void can also be used as an air ‘plenum’, in which the void itself forms a pressurised ‘duct’ to supply air or extract it from the occupied space below.
Suspended ceilings can allow easy access to services by the removal of tiles, or through access panels and can allow flexibility of layout of spaces below. However, they do result in some loss of headroom (generally at least 100mm).
Typically suspended ceilings are hung from a bracket fixed to the underside of the floor slab supporting a series of interlocking metal sections that form a grid into which panels such as ceiling tiles can be fitted. Beam systems are also available, in which tiles are laid between parallel beams rather than a grid, and there are a wide range of different grid profiles and tile edge details that can be used to allow the grid to be exposed, flush, recessed or concealed.
Tiles may be manufactured from materials such as mineral fibre, metal, plasterboard and laminates and are often perforated to provide specific levels of acoustic absorption that can be used to control the reverberation time in spaces below. Typically ceiling tiles are 600mm by 600mm or 600mm by 1200mm, although a range of sizes are available, as well as bespoke panels such as moulded panels, and complex systems that might include acoustic baffles, dropped panels, integrated service modules and so on.
Careful design is required to ensure integration with partition systems so that tiles, grids and partitions intersect neatly.
Partitions may stop at the underside of the suspended ceiling to provide maximum ease of installation and flexibility, or may run through the ceiling to the underside of the floor slab. Where partitions do not run through the ceiling void, care must be taken to ensure that a flanking path is not created for the transmission of sound between adjacent spaces or for the spread of fire. Acoustic insulation or fire separation can be provided in the ceiling void if necessary.
The selection of suspended ceilings may depend on:
- Aesthetic considerations.
- The requirement to incorporate fittings necessary for building services.
- Requirements for acoustic attenuation and absorption.
- Hygienic requirements.
- The need to provide fire separation.
- Moisture resistance
- Corrosion resistance
- Cleaning requirements.
- Thermal insulation.
- Tile thickness and size.
Approved Document B2, ‘Fire safety: Buildings other than dwellinghouses’, defines a suspended ceiling (fire-protecting) as '...a ceiling suspended below a floor, which contributes to the fire resistance of the floor'. Appendix A, Table A3 of the approved document classifies different types of suspended ceiling.
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