Tim Vincent of Rockwool explains why specifiers should consider non-combustible stone wool insulation in multi-storey buildings.
Buildings over 18 metres in height present numerous challenges when it comes to insulation requirements and fire safety standards. Given that most fires occur in domestic dwellings, high-rise residential buildings over 18 metres have a high safety risk potential in the event of a fire due to the long escape time for occupants to travel from the top of the building to safety. Meanwhile, today’s modern multi-storey buildings tend to offer a complex mix of occupation, including offices, hotels, residential, retail and leisure facilities, which can present further challenges in the event of a fire.
Increased fire risk in high-rise buildings
The time to evacuate a high-rise building is extended due to the large volume of people attempting to escape at one time, especially as lifts and escalators are usually inaccessible in the event of a fire. This not only presents problems in terms of the speed of evacuation, it can also put those with mobility issues at an increased risk.
In this type of building, fire can quickly spread through the material of an external cladding system or through the cavities. Typically, the source of ignition may be flames issuing from windows or other openings due to a fire within the building, or there may be an external fire source – for example, fire radiation from another building or from a source immediately next to the cladding, such as refuse set alight by arson. Flames in cavities can extend 5 to 10 times original length, regardless of materials present. They can flash over and break out through windows, spread up over or through the cladding or extend over 2 metres above a window opening. There is also increased risk during construction when the insulation is exposed.
Careful consideration of the design and products specified to reduce the fire risk in such buildings is required with particular emphasis on containment to allow safe evacuation, reduce the risk of fire spread to other buildings and to enable access for fire fighters.
BR 135 and fire safety standards
Fire safety standards, embodied in Building Regulations Part B Fire Safety and associated Approved Documents, are designed to ensure that adequate fire safety provisions are incorporated in tower blocks of whatever type. Regulation B4 requires the external walls of a building to adequately “resist the spread of fire” with functional requirements given in Approved Documents. In any building, the cladding system and materials must conform or exceed the regulation for limited combustibility defined in BR 135: “Fire Performance of External Insulation for Walls of Multi-Storey Buildings”, when tested in accordance with BS 8414-1:2002 and BS 8414-2:2005 for its range of external wall insulation systems. This testing satisfies building regulations in England & Wales and Scotland pertaining to fire for buildings over 18 metres tall. The BR 135 classification is called for as an alternative guidance to non-combustibility compliance for domestic and commercial applications.
With the completion of a number of construction projects not compliant with Approved Document B or the guidance under BR 135, the Building Control Alliance in conjunction with its members looked to readdress misunderstandings within the market. In June 2014, the BCA published the first issue for guidance note 18, which addressed the key issues surrounding external wall materials, including ‘Class O’ performance and the various routes for compliance. Following this revision, the NHBC now include a fourth option for compliance, published in their technical bulletin echoing the risk of fire spread within external wall constructions.
As a publicly available document, Guidance Note 18 is useful to everyone within the construction process looking to mitigate risk and advises that “As a guide, insulation of limited combustibility should be used e.g. Rock mineral fibre type, stone wool, slag wool or man-made mineral wool/fibre.”
The straightforward route to demonstrating compliance with BR 135 and Guidance note 18 in our view is to use stone wool insulation that is non-combustible. Non-combustible products will not contribute in any stage of the fire, including a fully developed fire according to the European reaction-to-fire classification standard BS EN 13501-1.
Stone wool insulation
Stone wool insulation products are used to create a firewall that slows down the spread of fire from room to room, improving safety, buying valuable time for occupants to safely escape as well as reducing the risk of property and asset damage. In addition, the insulation does not produce toxic smoke and therefore reduces the effects of smoke damage to the building too. As the biggest cause of death during a fire, this is a key advantage for many specifiers when choosing specified products.
Manufactured from basalt rock, stone wool insulation consists of layers of bonded, water-repellent-treated multidirectional stone-wool fibres formed into a resilient batt using a resin binder. It can achieve a reaction-to-fire rating of A1 under the British and European standard for the fire classification of construction materials BS EN 13501-1: 2007, or “non-combustible.”
Resources
To support this BR 135, Rockwool has produced a technical publication entitled Routes to Compliance in High Rise Buildings over 18 metres. There is also a Rockwool RIBA Accredited CPD, entitled “Fire safety compliance: Rainscreen Cladding Systems”.
Tim Vincent is head of technical for Rockwool.