Raised access floors are elevated structural floor systems built above a solid substrate – most likely concrete – that create a void for hiding mechanical and electrical (M&E) services.
Raised access floors are sometimes called access floors, computer floors, platform floors, raised floor systems, or suspended flooring.
With adjustable pedestals, they create easy access for building maintenance and retrofitting.
You’ll often find them in large buildings like hospitals, where having a cavity barrier system at specific distances is essential, but also in service rooms and data centres.
Basically, areas with high-density cabling or underfloor heating, ventilation, and air conditioning (HVAC).
This Knowledge Hub article first explains these systems in more detail, then covers tested solutions available to provide a cavity barrier and meet regulatory requirements.
Key aspects of raised access flooring
The structure of an access floor consists of adjustable pedestals, optional steel stringers that connect the pedestal heads to form a grid-like (solid!) structure, and removable modular panels.
Two main benefits of this system are that it improves aesthetics by concealing wires and offers flexibility for any required building changes, especially in buildings like hospitals that cannot stop operating.
The panels are often made from a chipboard core with a steel outer, though other options are available.
How to firestop raised access floors?
Using cavity barriers for gaps
Because access floors create a hidden void, cavity barriers are required to prevent the spread of fire, typically for a 30-minute integrity (E 30) and 15-minute insulation (I 15) fire-resistance rating.
Careful consideration must be given to where these types of floors are used when it comes to compartmentation lines, as they are typically not suitable for under walls or door thresholds.
Approved Document B, Section 8: Cavities – Flats, page 70, states that “it is not appropriate to complete a line of compartment walls by fitting cavity barriers above or below them.” For further information, view the Cross Report 1181.
- Fire-rated walls and screens: Must maintain compartmentation and be designed for installation at full height. Raised access floors are not fire tested with supporting walls above them, so the correct application is for the raised access floor to stop on either side of the wall.
- Fire doors: These are tested to specific fire-resistance test standards, which differ from those used for raised access floor systems. The platform floor would again stop on either side of the fire door threshold, abutting the supporting construction, such as a four-sided flexible partition (if appropriate) or a masonry/concrete upstand.
An access floor may be used for compartmentation lines in open spaces such as hospitals, data centres, airports, or shopping centres, where compartmentation lines may not be visible.
This is because they are formed above the raised access floors by shutters or fire curtains that drop to create dedicated compartmentation lines in the event of a fire.
So, where appropriate, the gap under the raised floor will require a cavity barrier system that meets the fire-resistance requirements of the building’s fire strategy.
Quelfire offers a solution using a single layer of QuelStop Fire Batt for gaps 590mm high with unlimited width (between suitable supporting constructions), which provides an EI 60 fire-resistance rating.
See the relevant tested detail: QB-RF00-S-00.
What about service penetrations?
As mentioned earlier, one of the purposes of an access floor is to create a void for hiding M&E services.
Therefore, it is imperative that where these cavity barriers under the raised access floor are going to be utilised, they can also provide protection for various service penetration types.
What’s particularly unique about Quelfire’s solution is its ability to be used with a large number of service penetration details, as assessed by our UKAS-accredited body.
This means that QB-RF00-S-00 can use any service penetration detail we’ve tested in a single layer of QuelStop Fire Batt.
Some service types may not have a single-layer QuelStop Fire Batt solution but do have a double-layer alternative.
If you want to utilise these service penetration details through a double layer of QuelStop Fire Batt, simply add two layers beneath the access floor and refer to QB-RF00-D-00.
This then allows for more service penetration options, including bus bars, trunking, cable trays, and the various service types that Quelfire has tested in a double layer of QuelStop Fire Batt.
The correct tested detail, installed in line with the manufacturer’s guidance and tested scope, helps protect both people and property.
If you have any questions about these details or their installation, please always contact our technical team. We’re always happy to provide fire stopping support and advice.
Frequently asked questions
Do raised access floors require firestopping?
Yes, raised access floors require cavity barriers to be installed at specified distances, as defined in the fire strategy.
At these points, systems like the QuelStop Fire Batt can be used. However, where service penetrations penetrate, a suitable Quelfire detail will need to be utilised.
What are the disadvantages of raised flooring?
Access floors have disadvantages, including high installation costs and reduced ceiling height. They are also susceptible to moisture damage, structural issues caused by heavy loads, and even pest infestations in the void.
Are raised access floors suitable for all buildings?
These systems are not suitable for all buildings, particularly in environments with high moisture, extreme loads, or where a solid floor construction is required.
