ASM Raised Access Flooring Most Frequently Asked Questions

.  What is a raised access floor system?

A raised access floor comprises of load bearing floor panels laid in a horizontal grid supported by adjustable vertical pedestals to provide an under floor space for the housing and distribution of services.
The floor panels are readily removable to allow quick access to the under floor services.


.  What are the key components of a raised access floor system?

The key components of a raised access flooring system can be defined as follows:

Floor Panel
This is the horizontal load bearing component of a raised floor. It is normally 24"x 24" square (industry standard module size) but can be 24" metric square.

These sizes are nominal sizes and clarification should be sought from the manufacturer as to their stated panel size and tolerances. These floor panels will be supplied as either bare finished to accept a carpet tile finish on site or, with a factory bonded finish.

This is the complete vertical, adjustable supporting structure to the raised floor panels. The pedestals are normally bonded to the sub floor using a epoxy resin based adhesive with mechanical fixings also provided if required. The pedestal assembly provides vertical adjustment of 1½" to allow the raised floor to be installed flat and level despite undulations in the sub floor. The pedestal head provides panel location and also when required a means of fixing the panel to the pedestal head.

This 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.


.  Where is a raised access floor used?

Raised access flooring is used today in a wide range of situations where there is a significant level of building services. Examples include:

Financial and Insurance offices where there is a need for a significant
    level of computer/telecom equipment.

.  National and Local Government offices, again there is a need for a significant
    level of computer/telecom equipment.

.  General administration buildings across the complete range of industries
    where the use of computer/telecom equipment is widespread.

Call Centers. Office environments set up to handle large-scale customer
     enquires thereby requiring significant levels of computer/telecom equipment.

Data processing centers. Large scale computer rooms set up for the processing
    of electronic data e.g. customer information, financial information.

Telecom switch centers. Old mechanical telephone exchanges now replaced by electronic
    switch facilities. Also new mobile technology requires new electronic switch facilities.

Distribution centers. These facilities distribute a vast range of fast moving
    consumer goods with order processing and such activities handled in a modern office environment.

Educational facilities. Raised flooring used in specific learning areas
    in schools, universities etc. Also used in library and major archive areas.

.  Retail facilities such as major department stores increasingly using
    raised floors surfaced with special finishes.

.  Industries requiring clean room facilities such as electronic and pharmaceutical.

.  Light industrial and specialist industries where flexibility and the use
    of under floor services would be advantageous.


.  Why use a raised access floor?

A raised access floor is used to provide a means of creating a void below floor level which is capable of ensuring building services are available at their required destination. These services will typically
include the following:

electrical power


.  telecom

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. That is the number of times that the office layout has to be modified to cater for changing requirements brought about by new technology, new personnel or new tenants to a building.


.  What are the benefits of using a raised access floor?

Raised access floors are used extensively to provide the following benefits:

.  Quick and easy access to the ever increasing volume of power, data and
     telecom services found within a modern building.

.  The underfloor void or cavity depth is often used as a large duct for HVAC systems.

.  In speculative buildings premises need to be adaptable for the needs of incoming occupiers.

.  Once occupied offices need to cater for office Churn and lend themselves
    to new office organizations and layouts with the redirection of services that implies.

.  Accessibility is a major consideration. People want easy access to the
    services for maintenance, rerouting or upgrading with as little disruption as possible to the work process.


.  What are the alternatives to using a raised access floor?

The alternatives are:

.  Suspended ceilings. High level trunking runs are above the ceiling and services drop down at the
             required locations through service poles. However any relocation, maintenance etc is at high level
             thus causing major disruption to the office area.

.  Pre-cast trunking. This method was common in the 1970s. Steel trunking is cast into the structural
             slab or topping screed along pre-defined runs. No flexibility to cater for future changes.

.  Skirting and Dado trunking. Steel or plastic trunking which runs around the perimeters of individual
             rooms. Adequate for small rooms but very limited for larger areas, also limited cable capacity.

.  Furniture. Specialist furniture which encompasses in-built service runs. Expensive and limited to
             vicinity of furniture runs.


.  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 held or loose lay products. Here 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 can be readily finished with factory bonded finishes.

.  Lock down or screw down products. In this case the floor panel is screwed or locked directly to the
             pedestal head thereby holding the panel in place and also providing lateral location. This 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.


.  What is the construction of a floor panel?

There are various basic floor panel constructions that are outlined below along with various attributes of each type.

Steel encased woodcore. This panel construction comprises of a high density particle board core that is encased by galvanized 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. By varying the thickness of the steel sheet and the strength of the chipboard core a wide range of structural performance is available.

Steel/cementitious panels. Here a structural steel shell comprising of a flat steel top and a profiled steel base are welded together to form a hollow shell. This shell is then filled with a foamed cement based core to give a panel that gives good structural performance in conjunction with excellent fire performance. In certain cases the hollow unfilled steel shell will provide a floor panel that gives suitable structural performance although its acoustic performance is limited.

.  What are stringers and why use them?

Stringers are introduced for various reasons each with their own specific design.

Snap on stringers. These snap onto the pedestal head and are used to provide additional lateral support to the raised floor. They are normally introduced at floor heights of 24" and above or for use with floor panels complete with factory bonded finishes. Snap on stringers are normally designed to increase the structural performance of the raised floor.

Bolt on stringers. These are screwed into the pedestal head and are designed as structural components and as such increase the structural performance of the raised floor system. They will also provide increased lateral stability.

Air plenum stringers. These stringers are designed only as a means of providing an air seal to the panel joints through the use of a gasket strip. They do not provide any increase to the lateral stability or structural performance of the floor.

Perimeter stringers. These provide additional support to cut panels around the perimeters if required by the project specification 

.  What is to be the use of the building in which the raised access floor is to be installed?

It is important that consideration is given to the intended use of the building as part of the evaluation process. Raised access floors are used in a wide range of buildings which includes the following:

General modern offices, any office environment where there is a need for a significant level of computer/telecom equipment.

Call Centers, office environment set up to handle large scale customer enquires thereby requiring significant levels of computer/telecom equipment.

Data processing centers. Large scale computer rooms set up for the processing of electronic data i.e. customer information, financial information etc.

Telecom switch centers. Old mechanical telephone exchanges now replaced by electronic switch facilities. Also new mobile technology requires new electronic switch facilities.

Distribution centers. These facilities distribute a vast range of fast moving consumer goods with order processing and such activities handled in a modern office environment.

Educational facilities, raised flooring used in specific learning areas in schools, universities etc. Also used in library and major archive areas.

Retail facilities such as major department stores increasingly using raised floors surfaced with special finishes.

The type of area in which the raised access floor will be used will help to define the structural performance required of the raised floor and also the specific type of finish required to the floor surface.


.  What level of services is anticipated under the raised access floor?

The anticipated use of the basic space in which the raised access floor is to be used will determine the projected level of power, data, telecom, HVAC and other services that will be located under the raised access floor. This information can then be used to determine the cavity depth required under the raised floor and hence the finished floor height which will then be used in specifying the raised access floor system.

.  What are the anticipated structural requirements of the raised access flooring in terms of static loads, rolling loads and pedestrian traffic?

It is important at an early stage in the consideration of a raised access floor that a detailed assessment is made of the likely loadings that will be imposed on the floor surface. These loadings need to be assessed in terms of:

Static loads:

.  Uniformly distributed loads

.  Point loads

Dynamic loads:

Rolling loads

.  Vehicle configuration and weight

Pedestrian traffic:

.  Areas of high traffic need to be determined.

.   This information can then be used to determine the structural requirements of the raised access floor.


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

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. This specification classifies raised flooring products by their structural performance. Installation issues are clarified by the Access Flooring Association Code of Practice and further clarification will occur when the National Building Specification K41 adopts this standard.

Other standards regularly in use are:-
CISCA. The North American specification which often travels with either the American client or American architects and is regularly used internationally. This is an industry driven specification and test method which is based upon individual component testing.


.  What type of surface finishes are available?

The following range of floor finishes is available:

Bare finish

Here the floor panel will not be finished with a surface covering. The surface of the panel will normally be the epoxy powder coated steel top sheet. This bare finished raised floor will normally be covered on site by the application of loose lay carpet tiles.

Factory applied finishes

The following finishes can be supplied factory bonded to the appropriate floor panel:


.  Anti static vinyl

.  Static conductive vinyl

.  Linoleum

High pressure laminate

.  Rubber

.  Carpet

.  Wood in various forms

.  Marble

.  Stone, ceramic tiles.

.  Other finishes may be available after evaluation.


.  What range of finished floor heights (FFH) is available?

Using standard pedestals finished floor heights from 3" to 48" are achievable. Bespoke solutions for lower and higher options are available.
As a general rule above a finished floor height of 24" stringers will be introduced to provide additional lateral stability.


.  What is the exact definition of finished floor height?

The finished floor height (FFH) is defined as "The nominal vertical dimension from the specified sub floor level to the specified finished floor level".

.  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 air 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
A typical air leakage rate for a raised floor system without a finish i.e. carpet tiles, would be in the region of 0.20 - 0.24 cfm/sq.ft. at a pressure differential of 0.12 inches of water.

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.

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.


.  What is a carpet location system?

Carpet location systems are where the carpet tile is fitted with small plastic location pips (normally four) which locate into location holes in the panel top surface. The carpet tile will be of the same module size as the floor panel and will be laid on the same grid as the raised floor panels (major air leakage). This has the benefit that in order to gain access to the under floor services the lifting of carpet and floor panels is kept to a minimum. However many experts would say that the quality of the finished carpet tile installation is inferior to a conventional off grid (minimal air leakage) carpet tile installation. Also the choice of carpet tile may be significantly limited and incur additional costs.


.  How is a raised access floor installed?

With regard to the physical installation of the raised access floor within a basic space there are two main issues:

Finished floor height and level. Within a single floor area a bench mark will be agreed between the floor installer and the main contractor. This bench mark will be directly related to the building bench mark. This will determine the height to which the raised access floor will be installed. The raised floor will be installed level to this BM by the use of rotating laser.

Set out of the raised access floor system. The set out of the raised access floor is an important aspect in ensuring that the raised floor operates satisfactorily throughout its anticipated life span. Depending on the size and shape of specific floor areas and size and location of any obstacles on the sub-floor a range of solutions can be sought. Raised access flooring panels are cut on site to fit at perimeter walls therefore a best fit situation can be sought using the appropriate floor panel module size. Ideally the setting out of the panels and pedestals can be coordinated by:

.  Working in line with other building modules to avoid regular obstructions.

.  Working out from the centre of an area.

.  Working to column centers.

Cut panels should ideally be cut just under a full panel width or a half panel width in order to minimize waste. Cut panels of less than 6" width should be avoided in order to maintain structural integrity. When it is not possible to avoid small cut panels the following solutions are available:

In-board cutting, the principle of maximizing the size of a cut panel by additionally cutting the last field panel adjacent to the perimeter. On certain product ranges and structural grades oversize panels are available as an alternative to the above.


.  What are the site requirements?

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

Dry and watertight areas at a temperature above 40° 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 epoxy resin 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; palletized materials typically weigh 1200 lbs and stand 48" high and are 26" 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 epoxy resin 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.

General working conditions include:

Work areas to be free of other trades and their materials.
Unloading and distribution. Access for elevators and tractor trailors to areas of hard standing directly adjacent to the building entrance or hoist facilities. Access suitable for pallet trucks from elevators and trucks 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.

· Work areas for the cutting of floor panels by the use of bandsaw.

· Adequate means for the disposal of rubbish and debris.


.  What are the potential timeframes?

The timeframes associated with the installation of a raised access floor are affected by many factors as outlined below:

· The size and shape of the areas into which a raised floor is to be installed.

· The exact specification of the raised access floor that is to be installed.

· General condition of the building.

· Poor quality of sub floor.

· Building program and sequence of installation amongst other works.

· Manufacturing times for raised floor components.

· Obstacles on the sub floor that have to be worked around.

· Availability of work areas.

· Unloading and distribution conditions.

· Availability and approval of necessary information.

Until these factors are suitably assessed for a specific project only then can installation timescales be evaluated. However an indicative installation rate of 300 sq ft per man 8 hr shift would be considered acceptable for an 'average' installation.


.  Is it necessary to apply protection to the raised access floor?

Various factors surround the use of protection in relation to raised access floor installations. Generally protection should be used:

To all installations where the floor panels have a factory bonded finish.
To all areas where the floor panels will be heavily trafficked prior to the installation of the soft finishes i.e. carpet tiles.

To areas where the floor panels will not be heavily trafficked prior to the installation of the soft finishes.

To areas where significant repeated access is required to the floor void for the installation of services.

Generally protection may not be required:

Materials commonly used for floor protection:

.  ¾" Plywood in sheet form

.  Hardboard in sheet form

.  Fire rated plastic sheet

.  Fire rated corrugated plastic sheet

These will be laid on the floor and if required the joints will be taped. ¾" Plywood will provide better protection against heavier levels of traffic. 


.  What building interface considerations are there?

The raised access floor will possibly interface with the following elements which will require consideration at the design phase:

.  Underfloor services

.  Thresholds at doorways/elevator lobbies, etc

.  Cladding/curtain walling

.  Perimeter heating

.  Skirting

.  Partitioning built off or through the raised floor

.  Changes in level e.g. ramps or steps


.  How level will the installed raised access floor be?

The raised access floor will be installed level within 1/16" in 10' x 10' area. 


.  Will the raised access floor require to be electrically earthed and how is this achieved?

In most cases due to steel used in its construction the raised access floor will require to be earthed in line with local conditions.


.  What happens to the floor panels at perimeters?

At perimeters the floor panels are cut to fit on site by the use of a bandsaw.

Gravity lay perimeter cut panels will be mechanically fixed to the pedestals to provide additional stability. The cut edge of perimeter panels will normally be supported by the use of perimeter stringers or additional pedestals. As a matter of course all cut edges at door thresholds etc will have additional support by the use of perimeter stringers or pedestals.


.  Is the concrete sub floor sealed prior to the raised floor installation?

There are occasions when the concrete sub floor will be sealed with 2 coats of a epoxy resin coating in order to provide a surface that will withstand a lot of traffic during the installation period and provide a totally dust free void. These are normally large and specialised computer/data processing type environments.


.  How to avoid problems associated with raised access floors?

As the raised access floor performs a critical function within the working office environment faults with the system can cause problems from simple annoyance through to major disruption. Many faults are rectifiable to a varying degree, however it is essential to consider the following key factors to prevent such occurrences.


.  Use of inappropriate products and/or solutions

.  Use of inappropriate class or grade of raised access floor

.  Poor quality products and/or installation

.  Raised access floor not lifted and replaced in accordance with manufacturer's instructions

.  Lack of appropriate maintenance.


.  Movement, rocking and squeaking of floor panels

.  Difficulty in removing and replacing panels

.  The floor may require modification in order to perform satisfactorily

.  Areas of floor or the complete floor may require replacement

.  Possible floor collapse with likely damage and injury.

In order to avoid the problems outlined it is important that the raised access floor be correctly specified at the outset. This specification should include not only the product requirements but also the installation requirements. Once installed the raised floor must be maintained correctly in line with the manufacturer's instructions.


.  How should a raised access floor be used?

Raised access flooring panels should only be lifted using the correct lifting device i.e. vacuum lifter or spiked carpet lifter. Panels should be lifted vertically with no hinging movement. Panels should be replaced in a vertical movement ensuring that the panel is seated on the pedestals correctly. Only single rows of panels should be lifted at any one time so as not to leave pedestals independent of panels, as they are prone to damage.


.  What are the maintenance requirements?

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.



This information is from Kingspan at


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