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Fire Safe Cladding for High-Rise Buildings

High-rise buildings present a number of interesting technical challenges for the external wall insulation system designer. In addition to experiencing greater structural movement and higher wind suction forces than low-rise buildings, high-rise structures are riskier in terms of fire propagation, and are less likely to see regular exterior maintenance than their low rise counterparts.

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. 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 (EWI) systems.

PermaRock has unparalleled experience in this market sector, with PermaRock Mineral Fibre EWI systems retrofitted to over 200 high-rise buildings throughout the UK over the past three decades.

We have produced a publication that considers some of the key differences between the systems most commonly specified and retrofitted as part of thermal improvement works on high-rise buildings and explains the advantages of direct fixed external wall insulation. In addition, the report demonstrates the safety in real-life situations where fires have occurred in buildings clad with PermaRock systems. 

Download Publication: PermaRock External Wall Insulation: Fire Safe Cladding for High Rise Buildings

UK Building Regulations 

In the UK, the Building Regulations require that buildings must be designed and constructed to adequately resist the spread of fire. This applies both to fire-spread over the walls, and from one building to another. The design must pay due regard to the height, use and position of the building.

In order to reduce the risk of fire spreading across a building’s façade, and to mitigate against ignition from external heat sources, the Approved Documents B of the Building Regulations recommend restrictions on combustibility of cladding materials. They also recommend the avoidance of extensive cavities in cladding systems applied to high rise buildings.

View the latest UK Building Regulations / Standards:

Fire safety: Approved Document B (England & Wales)
Technical Handbook 2: Domestic - Fire (Scotland)
Technical Booklet E - Fire Safety (Northern Ireland)

Retrofitted High-Rise Cladding

In the UK there are essentially two widely used cladding options retrofitted on existing multi-storey buildings, rainscreen or back-ventilated systems and rendered external wall insulation.

Rainscreen or Back-ventilated Cladding Systems - with rainscreen or back-ventilated systems, the thermal insulation is fixed tight to the wall face, but there is a cavity between the insulation and the external cladding panels (which could be made of metal, aluminium composite material, cementitious board, stone, terracotta, etc.) These panels are held away from the face of the insulation on metal or timber rails. The rails are attached to brackets which penetrate through the insulation layer and which are fixed to the substrate. A drained and ventilated cavity is thus formed between the cladding panels and the insulation.

Insulation materials in rainscreen systems can be non-combustible (e.g. stone wool) or rigid polymer foams (e.g. phenolic or polyisocyanurate (PIR)) neither of which are classed as non-combustible, but which may exhibit low combustibility when fire tested. If the insulation is not deemed ‘non-combustible’, the system must incorporate suitable fire barriers so that in the event of a fire entering the system, the fire is prevented from spreading up the cavity. Fire entering the cavity of a rainscreen system can result in a “chimney effect” whereby fire propagates rapidly up the cavity, ‘leap frogging’ from window opening to window opening. Fire-stopping measures within the cavity are therefore essential, and the cladding materials themselves must have appropriate fire resistance properties to prevent fire spread.

Rendered External Wall Insulation Systems - those which are directly attached to the wall face and which are ‘face-sealed’ to prevent weather penetration. PermaRock external wall insulation systems fall into this category.

External wall insulation (EWI) systems with render finishes behave rather differently than rainscreen or back-ventilated systems, although consideration must also be given to ensuring that the systems meet the requirements of the Building Regulations in relation to fire, as well as thermal performance, moisture, etc.

For high rise, multi-storey buildings, PermaRock advocates the use of PermaRock Mineral Fibre EWI Systems

These systems incorporate PermaRock Mineral Fibre insulation, a non-combustible (Euroclass A1 to BS EN ISO 13501-1:2007 + A1:2009). stone wool insulation in the form of rigid batts which are directly attached to the wall using a combination of adhesive bonding and mechanical fixing. A fully reinforced, polymer-enhanced cementitious basecoat is applied directly onto the insulation. In recognition of the guidance provided in BR 135, PermaRock systems also employ non-combustible, stainless steel fixings to additionally anchor the reinforced basecoat to the substrate in addition to the adhesive bonding and mechanical fixings used to attach the insulation to the substrate. This helps to maintain the stability of the system (in the event of a fire), thereby helping to keep the building protected and ensuring safe access for emergency services.

PermaRock Mineral Fibre External Wall Insulation Systems - Fire Performance

PermaRock Mineral Fibre EWI systems are suitable for use on buildings up to and those with floor levels above 18m above ground level and have been fire tested by BRE Global to BS 8414 and assessed as satisfying the requirements of BR 135 - ‘Fire performance of external thermal insulation for walls of multi-story buildings’.

These systems also achieve a “Class O” classification under the Building Regulations Approved Document B.

The fire safety credentials of a PermaRock Mineral Fibre EWI system has also been demonstrated in the Fire Resistance test of BS 476 Part 22 where it achieved over 2 hours resistance and integrity. PermaRock can confidently assert, therefore, that PermaRock Mineral Fibre EWI systems can be considered fire safe. They are therefore highly unlikely to contribute to the spread of fire across the façade or within a building onto which they have been applied.

Fire Safety Evidence

BRE Global Ltd, which carries out fire investigations on behalf of the UK government, has investigated several fires in multi-storey buildings and some of these have been documented in its report, entitled ‘External Fire Spread – Part 1 Background research’, BRE Global Ltd., April 2016.

Download BRE Global Report

Whilst external fire spread has occurred in some of the case studies featuring other manufacturers’ systems, BRE acknowledges that a PermaRock Mineral Fibre EWI system, installed on a multi-storey high rise residential block in Glasgow, resisted fire and actually prevented the fire spreading across the building façade. The fire, which developed on the 11th floor of the 22-storey building, broke out of the windows, exposing the PermaRock EWI system to the force of the fully developed fire. Damage was localised to the immediate vicinity of some of the windows but, beyond this, the effects were limited to surface charring and sooting.

Similar fires have occurred on other high-rise multi-storey residential blocks and, in all cases, the PermaRock Mineral Fibre EWI systems have proven to be robust and resilient. They have always prevented fire spread and have remained securely attached to the wall face, thereby allowing safe access for Fire & Rescue Services.

Department for Communities and Local Government - Building Safety Programme

The Department for Communities and Local Government (DCLG) has established the Building Safety Programme to assist landlords and building owners identify buildings which are of concern through a thorough checking and testing process.

For the latest information and advice please visit the DCLG’s Building Safety Programme website.

Find out more

For further information on PermaRock Mineral Fibre EWI Systems or to see examples retrofitted to high-rise blocks, please visit www.permarock.com or call PermaRock’s technical support team on 01509 262924.

For high rise, multi-storey residential buildings PermaRock recommends the use of the PermaRock Mineral Fibre External Wall Insulation System.

This system comprises adhesively bonded and mechanically fixed PermaRock Mineral Fibre insulation which is non-combustible (Euroclass A1 to BS EN ISO 13501-1:2007 +A1:2009). 

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