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FAQs

We've put together some common queries that our customer often have regarding access floors and their capabilities. Click on the questions below to display the answers.


Why use a raised access floor?


A raised access floor provides a void below floor level which is capable of routing building services to their required destination. These services will typically include the following;
  • electrical power
  • data
  • telecoms
  • HVAC; environmental control / air conditioning
  • fire detection and suppression
  • security
  • water and drainage.
The use of a raised access floor will allow quick and easy access to these services for maintenance reasons. Also in today’s modern office environment Churn is a major issue. Churn is the number of times that the office layout may be modified to cater for changing requirements brought about by new technology, new personnel or new tenants to a building.

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What types of raised access floor are available?


There are two basic groups of raised access floor system available each with their own advantages;
  • Gravity or loose lay products, where the floor panels rest on the pedestal head. The panels are held in place by their weight with lateral location providing engagement between panel and pedestal head. These systems allow very quick and easy access to the floor void and the panels accept factory bonded finishes such as vinyl or carpet.
  • Lock down or screw down products, where the floor panels are screwed or locked directly to the pedestal head thereby holding the panel in place and also providing lateral location. This type of system provides a very solid and rock free floor with quick and easy access to the floor void. However these systems cannot accept factory bonded finishes
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What range of finished floor heights (FFH) is available?


Using standard pedestals finished floor heights from 70mm to 1200mm are achievable. Bespoke solutions for lower and higher options are also available.
 
As a general rule above a finished floor height of 600mm stringers are used to provide additional lateral stability. Stringers are generally 30mm deep and as such will reduce the clear void available for services by the same dimension.

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Are there any standards governing the use of raised access floors?


The PSA MOB PF2 PS/SPU specification was initially produced by the Property Services Agency (PSA), one of the first large users of raised access flooring within general office areas. This document is a comprehensive performance specification covering both the products and their installation. It is based upon complete system testing i.e. floor panels supported on their pedestals. The standard has become the de facto specification for the UK raised floor industry.

With the Property Services Agancy now disbanded the copyright and custodianship of the standard now resides with the Access Flooring Association.

The National Building Specification, NBS K41 covers the design, supply and installation of raised flooring; it cross references to the PSA specification & BSEN 12825 with regard to product performance. This document is widely used throughout the UK.

In August 2001 a European Standard was issued after several years of consultation between all the European manufacturers and was adopted as a British Standard in November 2001, BS EN 12825. The use of this standard is increasing as it provides specifiers with increased flexibility. BSEN 12825 classifies raised flooring products by their structural performance. Installation issues are not included within BSEN 12825 so it is appropriate to consult an expert or use the National Building Specification K41.

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Why are raised floor voids used as air plenums and what are the important criteria?


In certain circumstances the available space between the underside of the raised floor panels and the sub floor surface (known as the plenum) will be used as part of the building’s heating and ventilation system. In these instances a pressure differential will be created between the air within the plenum chamber i.e. under the floor, and the air above the floor in the office environment.

Product considerations
In these situations there are certain attributes of the raised access floor that become important. The leakage of air through panel joints and at perimeters will need to be kept within specific parameters for the required air pressure differential. The air leakage rate through the panel joint line is dependant on the size of gap between the panels, which is dependant upon the manufactured quality of the panel edge detail and also the quality of the raised floor installation. The air leakage at perimeters is also dependant upon the specific detail design and the quality of the installation.

Air leakage rates for under floor air systems
Some HVAC systems operate at high pressure, 25-30pa and in these instances the air leakage rate for a raised floor system without a finish i.e. carpet tiles, should be considered and advice sought from the manufacturer.

With an HVAC system operating at low pressure, e.g. 7-15pa the air leakage through a raised floor will be of a lesser importance but again advice should be sought from the manufacturer.

Air seals
Where the permitted air leakage rate through the raised access floor complete with the required floor covering is very low, or the specified air pressure differential is high, the raised floor in its standard form may not suffice. In these instances the raised floor panels may be fitted with neoprene or similar gaskets to their edges in order to form a seal when installed against other similar panels. Alternatively stringers fitted with gasket seals may be installed to seal the panel joint lines.

Type testing
The air leakage rate through a raised access floor can be determined by laboratory testing in order to give indicative air leakage rates through both the panel joint lines and perimeter detail. This can be undertaken at a project specific pressure differential or across a range of pressures.

Site testing
Alternatively the raised floor can be tested in its entirety on site, as part of the installation process. This on site testing can determine not only the air leakage through the raised floor but also the leakage through the floor void via other means e.g. incorrectly sealed service penetrations through the sub floor slab. Obviously the cost of testing on site can be prohibitive and in this case indicative results may be acceptable.

Air outlets and distribution
The conditioned air within the floor plenum is delivered into the area above the floor via a range of outlets. These are usually aluminium grilles of the same module size as the floor panels. Dampers may be fitted to allow control of the airflow through individual grilles in order to achieve localised control to suit specific local requirements. Perforated floor panels can be used again fitted with dampers if required as an alternative to grilles. A further alternative is use of smaller circular air diffusers fitted into the floor panels, again fitted with dampers to allow adjustment locally to suit specific requirements. All of these air outlets are readily relocated within the raised floor area as requirements change.

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What about the acoustic performance of the raised access floor?


There are situations where the acoustic performance of the raised access floor is of importance with regard to its ability to dampen the transmission of airborne sound between adjoining rooms. The use of partitioning and stud wall systems mounted off the raised access floor, thus creating a clear void under partition walls does make the acoustic performance of the raised floor of significant concern in sound sensitive installations.

Product attributes
In these instances there are certain attributes of the raised access floor that become important. The construction of the floor panel with regard to the component materials is an issue with regard to the overall acoustic performance, as is the edge profile of the panel. The passage of sound between adjacent panels is dependant on the level of gap between the panels. This is dependant upon the manufactured quality of the panels and also on the quality of the raised floor installation.

Performance Considerations
An indicative performance of the acoustic properties of a raised access floor system can be derived from laboratory testing. In these tests an area of raised floor is installed within a acoustic room and a standard partition wall is constructed off the raised floor. As the acoustic performance of the room and wall are known the only variable i.e. the raised floor, can be evaluated. The transmission of airborne sound from room to room through the raised floor is measured at a range of frequencies. These measurements allow the Floor Normalised Level Difference to be determined across the test frequency range. This range of test data is brought back to a single figure known as the Weighted Floor Normalisation Level Difference that can be taken as the measurement of the amount by which the raised floor will reduce airborne noise between adjacent rooms. Generally these tests will be conducted on the raised floor alone, then with the addition of a barrier under the partition line, and then with the addition of carpet tiles on the raised floor.

Site Considerations
When required on site testing can be undertaken to determine the airborne sound transmission between adjacent rooms. However in these situations the raised floor is being measured in conjunction with the installed partitioning and the installed suspended ceiling system. Whilst each individual system e.g. raised floor, partition, ceiling may have its own test report on its acoustic performance it is difficult to determine the performance of their combined installation. Consequently in critical installations laboratory testing of a sample installation i.e. raised floor, partition, ceiling etc should be considered. Obviously the cost of testing on site can be prohibitive and in this case indicative results may be acceptable.

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What are the site requirements for a raised floor?


The following site conditions are required for the installation of a raised access floor:-

Dry and watertight areas at a temperature above 5°C and a humidity below 75 % RH. This is required for both the installation works and also for material storage.

Sub floor to be in the following condition;-

  • Free from wet or dry contamination.
  • Able to accept pedestal adhesive and if required mechanical fixings.
  • Any holes, joint lines etc. in higher level sub floors should be sealed in order to prevent floor sealer leaking through to the level below.
  • The sub floor should be structurally strong enough to support the raised access floor and the environment it supports.
  • The sub floor is required to be structurally strong enough to allow the storage of raised floor materials prior to installation (note; palletised materials typically weigh 400kgs and stand 1200mm high and are 650mm square).
  • The surface of the concrete sub floor should ideally be of a medium tamp finish in order to give a reasonably flat surface without inducing the formation of weak surface laitance.
  • A power float finish will normally give a excessively smooth surface which will prevent the dust sealer and the pedestal adhesive obtaining a good key and hence good bond onto the floor surface. In order to achieve a good bond onto a power float finish the subfloor will require to be suitably prepared by mechanical means which will remove weak surface laitance and provide a suitable surface for the application of floor sealer and pedestal adhesive.
  • Light weight structural sub floors such as Lytag need to be treated with caution with regard to their compressive strength and also the fixing of pedestals to their surface as failure can occur due to the weakness of the sub floor rather than the integrity of the pedestal fixing.
General working conditions include:-
  • Work areas to be free of other trades and their materials.
  • Unloading and distribution.
  • Access for lorries and vans to areas of hard standing directly adjacent to the building entrance or hoist facilities.
  • Access suitable for pallet trucks from lorries and vans to distribute all materials including a hoist if appropriate to all points of the installation.
  • Any changes in level in the sub floor should be overcome by temporary ramps at a gradient not exceeding 1: 8.
  • Adequate power supply to all work areas.
  • Adequate safety lighting to all work areas.
  • Water supply for dilution of sub floor dust sealer.
  • Work areas for the cutting of floor panels by the use of bandsaw.
  • Adequate means for the disposal of rubbish and debris.
  • Welfare facilities

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What are the maintenance requirements for a raised floor?


The exact maintenance requirements for any specific installation will be clearly spelled out in the Project Operating & Maintenance Manual. This will take due regard for the products and floor finishes used and also the anticipated loadings on the floor in terms of static loads, rolling loads and pedestrian traffic.

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What is the expected life span of a raised access floor?


The expected life span of a raised access floor system is outlined in the PSA MOB PF2 PS / SPU specification as:-
  • The supporting components should have a minimum life of 50 years.
  • The floor panels (excluding floor finish) should have a minimum life of 25 years.
There is no mention of life span in the BS EN 12825 standard although it can be reasonably expected that the raised floor has a life span in keeping with the period of time between major refurbishments of the building which may be 25 years.

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Kingspan Access Floors
Burma Drive
Marfleet
Hull
HU9 5SG


Tel: +44 (0) 1482 781701
Fax: +44 (0) 1482 799272

info@kingspanaccessfloors.co.uk