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Five ways the ban on combustible materials will affect architects

Grenfell anthony coleman
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This week the government announced it was banning combustible materials on new high-rises. With details still to emerge, PRP’s Andrew Mellor explores what the measure could mean for architects

After a lengthy consultation, and 15 months on from the Grenfell fire, housing secretary James Brokenshire yesterday (1 October) announced a ban on the use of combustible materials in exterior walls of new residential blocks above 18m as well as in care homes, student accommodation and hospitals.

Details on the policy, including when the ban will be implemented, are not expected until late autumn, but the Ministry for Housing Communities and Local Government (MHCLG) has since confirmed it will limit the use of materials in the external walls to products achieving a European fire-resistance classification of Class A1 or A2 (see below).

A1 and A2-rated materials include solid metal, brick and glass which rarely contribute to fires, or plasterboard, which makes no significant contribution. It is understood that the ban will not be retrospective.

The measure will usher in a regulatory change that will signal a major upheaval in the building industry. In the meantime, inherently safe solutions are already being widely adopted, with brick becoming more popular than ever – a clear demonstration that fire safety is strongly influencing architectural responses to façade design.

Here are five potential impacts of the government’s ban:

1. Insulation and CLT

A ban on all materials except those with an A1 or A2 rating would prevent the use of insulation products such as EPS [polystyrene], phenolic and PIR (polyisocyanurate) in building façades. A consequential impact of only being able to use non-combustible insulation is the potential increase in wall thickness, one that many architects will have already recognised post-Grenfell, with walls being drawn wider at planning application stage in anticipation. If the wall thickness cannot be increased, perhaps due to site constraints, then thermal performance will be reduced. While the policy is unclear about whether ‘exterior wall’ includes the complete wall assembly, the change could have implications for cross-laminated timber (CLT). One potential outcome could be that timber frame or CLT systems will not be able to be used for buildings with a floor level more than 18m above external ground level.

2. New products

A ban on materials at any level of combustibility rating would lead to some façade components being excluded, as there are simply not products on the market that achieve the required higher levels of fire reaction performance. Examples include EPDM [membrane made of synthetic rubber] and vapour barriers. Of course, architects cannot design a fully functioning façade properly without these components, so there may have to be initial exemptions to any ban, perhaps determined by the time it takes manufacturers to produce new compliant products. As we understand, there are very few breather membranes which are rated A2, possibly only one product, so demand will be high and material shortages could be experienced in the short term.  

3. Balconies

Individual amenity balconies on residential buildings are not considered by the guidance in Approved Document B Volume 2. Traditionally these have often included timber or other combustible components and sometimes laminated glass balustrades. If balconies were included in a materials ban, then timber could no longer be used. Laminated glass can at best be A2-rated, as its rating is influenced by the content of the lamination layer, so it would therefore need careful specification. In addition, thermal breaks used to separate the building structure from the balcony structure are made from combustible materials and so an alternative will therefore need to be sought to meet the requirements of a holistic ban on combustible materials in façades. We are already experiencing clients requesting that balcony decks are constructed from non-combustible materials. 

4. Client response

Many clients do seem to have a greater focus on fire safety since the Grenfell tragedy in relation to both the design solutions and the processes involved with checking the quality of construction work on site. Some clients have been requesting only A1 or A2 materials in façades for the past year. Another consideration is how compliance is evidenced to third parties, such as insurers and mortgage providers. Recently they have been asking for BR135 compliance to be proven (this is related to BS8414 large-scale fire tests - see Testing, below) and this could now change to individual façade component test results. Clients are already focusing on the ‘golden thread’ as set out in the Hackitt Review and what this means for data and evidence collection, to ensure their buildings have a robust and accurate digital record.

5. Testing

The recent MHCLG circular letter has effectively stopped the use of written assessments, leaving just two routes to demonstrate compliance. The ban announced this week implies an end to the use of BS8414 tests. If the ban allows only the linear route to compliance, then large-scale fire tests for façades could be a thing of the past. Architects will quickly need certainty of the route to compliance from government but also across building control bodies, because the industry is currently experiencing very mixed approaches from inspectors. 

Outstanding issues

The key questions are what the ban means for buildings currently being designed, those under construction and those that are already occupied. The process for introducing a ban could affect projects being designed which do not yet have a Building Regulations application registered or a Full Plans approval.

Both could mean redesign work and possibly amendments to planning consents. Another concern is what the ban will mean for other types of buildings, such as hotels, offices or rental and mixed-use developments. There continues to be uncertainty on which façade components will be included in the ban, which façades solutions will be compliant and how compliance can be demonstrated. Clarity needs to be provided by government soon.

PRP partner Andrew Mellor heads the practice’s development consultancy and is the technical lead on its work for MHCLG on Building Regulations analytical research

What does A1 and A2 rating mean?

The government’s official guidance to rules on fire safety – Approved Document B – defines products achieving an A1 classification as non-combustible and products achieving an A2 classification as being of limited combustibility. A-class products – those classified A1 and A2 – make no significant contribution to fire growth, while products with a rating of B-F are are classified as combustible.

The European Classification system for combustibility classifies construction products using a series of tests. Class A materials have the best performance in a fire and is divided into two sub-classes, Class A1 and Class A2.

Class A1 Products are described as having no contribution to fire at any stage. The BS EN 13501 test sets several thresholds for combustion performance when tested to both EN ISO 1716 and EN ISO 1182. One of these thresholds is a maximum heat of combustion of 2MJ/kg. Typical products meeting this classification include most inorganic materials such as metal, stone, and glass.

Class A2, s3, d2 Products are described as having no significant contribution to fire at any stage. BS EN 13501 sets several thresholds for combustion when tested to EN ISO 1182, or both EN ISO 1716 and EN 13823. One of these thresholds is a maximum heat of combustion of 3MJ/kg. A typical product meeting this classification is plasterboard.

An A2-certified product has a higher combustibility and can sustain flame for no more than 20 seconds. In contrast, A1 has a lower combustibility and no sustained flaming when tested. 

  • 2 Comments

Readers' comments (2)

  • If, as it seems, this policy includes a ban on the use of timber cladding systems, and timber construction systems, in buildings over 18m high, this will have terrible consequences for the environmental impact of construction in the UK.

    At a time when we should be transitioning away from a predominance of steel and concrete in construction, this would unnecessarily limit the palette of materials available to those that have high embodied energies. I'm all for a ban on materials such as the PE in the Grenfell cladding system, that acted like petrol in helping the spread of the fire up the facade, but including things like CLT or engineered timber frame systems in a blanket ban on external walls seems a bit ill considered.

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  • As usual a lack of clarity leads to speculation. A clear definition of where the external wall begins and ends would help. Is it for instance outside a line of cement particle board, which has a rating of A2 typically. Would this then allow timber based structure as suggested above?

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