External Wall Insulation: Fire Safe Cladding for High-Rise Buildings

In the wake of the Grenfell Tower tragedy, private and social landlords, building owners and other property stakeholders, have naturally placed a renewed emphasis on fire safety, particularly in respect to high-rise buildings, to ensure residents feel safe and are safe. Over the past few months this has resulted in an increase in concerns about the fire safety ratings of different cladding systems.

In particular, building owners and specifiers have been keen to understand how performance varies between back-ventilated rainscreen cladding, for example systems that employ Aluminium Composite Material Cladding (ACM), and other options, such as directly fixed external wall insulation systems. In response, PermaRock has published a document that considers some of the key differences between the systems most commonly specified as part of thermal improvement works on high-rise buildings and explains the advantages of direct fixed external wall insulation.  

Entitled "External Wall Insulation: Fire Safe Cladding for High-Rise Buildings", the 8-page document can be downloaded here.

The publication describes the two widely used cladding options retrofitted on existing multi-storey buildings and provides an overview of the performance characteristics of the systems. The first - generally termed 'rainscreen' or 'back-ventilated' systems - feature an air cavity between the protective decorative cladding and the insulation (which is directly attached to the face of the wall). The air cavity requires effective fire-stopping measures in order to prevent fire from spreading within the cavity and creating a dangerous 'chimney effect'. 

By contrast, directly fixed external wall insulation (EWI) systems with render finishes, have no cavity. The insulation is attached directly to the face of the building by both adhesive bonding and mechanical fixing with a reinforced weatherproof render applied directly over the insulation boards, producing a monolithic, continuous system with no air gaps and therefore eliminating the risk of the ‘chimney effect’ occurring.

For high rise, multi-storey buildings, PermaRock advocates the use of mineral fibre insulation. PermaRock mineral fibre insulation is non-combustible, with a Euroclass A1 rating to BS EN ISO 13501-1:2007 + A1:2009.

The systems are suitable for use on buildings with floor levels above 18 metres above ground level and PermaRock mineral fibre EWI systems are tested to BS 8414 to satisfy the requirements of BR 135 – ‘ Fire performance of external thermal insulation for walls of mulitstorey buildings ’ and also achieve a 'Class O' classification under the Building Regulations Part B for fire-spread across the surface.

PermaRock has a demonstrable track record of over three decades, with PermaRock mineral fibre EWI systems retrofitted to in excess of 200 high-rise blocks throughout the UK over this period.

Importantly, the fire safety performance of PermaRock's EWI systems has been proven in a number of real-life situations where fires have occurred in buildings clad with PermaRock systems.

For example, BRE Global Ltd, which carries out fire investigations on behalf of the UK government, reported on a fire that broke out on the 11th floor of a 22-storey building in Glasgow which was fitted with a PermaRock mineral fibre EWI system. The report acknowledged that the system resisted a fully developed fire and prevented it from spreading across the building façade. As the accompanying image shows, the fire broke out of the windows and the EWI system prevented it from spreading externally. External damage was localised and largely cosmetic, being limited to surface charring and sooting.

In this and other instances, PermaRock mineral fibre EWI systems have proven to be robust and fire safe, preventing fire spread and remaining securely attached to the building.

For more details of the Glasgow fire safety investigation please refer to the BRE report. (C. Holland, D. Crowder & M. Shipp - ‘External Fire Spread – Part 1 Background research’, BRE Global Ltd., April 2016 - download here)

Further information and advice can be found on the PermaRock website or by contacting PermaRock's technical support team on 01509 262924 or by email.

Examples of PermaRock EWI systems installed onto high-rise blocks can be viewed here.