Medium grade V Medium Duty - Raising up the question!

17 July 2020

Medium Grade vs Medium Duty? So what on earth is the difference? Even the names are pretty similar but there is a difference and worth keeping an eye out on what is actually specified and being offered.

The Property Services Agency (PSA) Method of Building Performance Specification 'Platform Floors (Raised Access Floors)', MOB PF2 PS , became the industry standard in the UK and has been for around 20 years until the recent arrival of the BS EN 12825:2001 specification.

This specification consists of performance requirements verifiable by standard testing procedures. Requirements covered include dimensional accuracy, moisture and thermal movement, strength grades, fire safety, floor panel finishes and electrical bonding and continuity. The latest edition being (March 1992) of the MOB PF2 PS was given the suffix SPU (single project use).

It was produced in conjunction with the Access Flooring Association (AFA) which RMF are a founder member and includes changes that affect nomenclature making it more relevant for non-government contracts; the performance requirements and test methods remain unchanged.

BSEN 12825 - Key Performance

In July 2001 a European Standard EN 12825 was approved by CEN as a voluntary specification for private projects and mandatory for public projects. This standard is now mandatory for all projects across the member states of the EU. This specification outlines classifications for raised access floor systems based on their ultimate load; this is the load at which failure occurs. The raised access floor system is tested to its ultimate load under the application of a 25mm x 25mm point load at a predetermined rate until failure occurs. During the application of this load the deflection of the floor panel is measured to produce a graph of applied load against deflection. This information is then used to determine the classification of the floor system. Raised floor systems are classified in terms of ultimate load, safety factor, deflection under working load and dimensional tolerances.

The classification system allows for six classes of ultimate load ranging from greater than 4kN to greater than 12kN. Against each of these six ultimate loads there is a choice of a safety factor of 3 or 2. Further for each of these ultimate load and safety factors three maximum deflections under working load conditions are available namely 2.5mm, 3.0mm and 4mm.

What BS EN 12825 does not intend to do is interpret the classifications or advise which class of raised access floor would be suitable for a specific application. The product application chart shown below gives guidance as to product classification against specific areas of application. These classifications are based upon the ultimate load determined in the manner prescribed within BS EN 12825. Further these classifications are based on a 2.5mm deflection under working load conditions and a safety factor of 3, these are best suited for most applications when taking due regard for the UK construction industry and the expectations of raised access flooring with regard to panel deflection etc.

Therefore a typical classification might be outlined as 3/A/3/2 where;-

3 is the ultimate load class in excess of 8kN

A is the deflection under instantaneous working load of less than 2.5mm

3 is the safety factor

2 is the dimensional tolerances classification

When specifications are produced for raised flooring they will highlight whether medium grade or medium duty is required, at RMF we ALWAYS adhere to the specification, we are aware some raised flooring contractors have specified medium duty to highlight a cost saving whilst not mentioning this to the contractor they are tendering for that it does not meet the specification. We pride ourselves on our ability to follow the specification and produce a fully compliant bid for the raised flooring packages.

Should you have any further questions on raised flooring specifications then please do not hesitate to contact our estimating teams at estimating@rmf-services.co.uk or call us on 01926 425289.

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