'Non-combustible' - Does what it says on the label?

20 December 2017 Kingspan Insulation UK
Approved Document B

Please note that the regulations and guidance mentioned in this article may have been updated since writing. Please visit our Fire Regulations page for the latest information.

So called ‘non combustible’ and ‘limited combustibility’ materials have been the focus of considerable discussion following the tragic fire at Grenfell Tower. 

Some have argued that the current building regulatory system should be stripped back to allow only these materials to be used on high-rise constructions. Before such a drastic course of action is taken, however, it is critical to consider whether it would actually improve the fire safety of our buildings.

Simplicity over safety?

As we discussed in a previous article, under current regulatory guidance façade systems comprising ‘limited combustibility’ or ‘non-combustible’ insulation materials are able to bypass large scale, full system testing. Instead, they can take a tick-box route which is arguably much less rigorous

The so called ‘Linear Route to Compliance’ is outlined in ADB2 Section B4-12 - Construction of external walls, for England and Wales, and THB2 for Scotland. It allows façade systems which use ‘non-combustible’ (Scotland) or ‘non-combustible’ and ‘limited combustibility’ insulation (England & Wales) to be deemed compliant on buildings over 18 metres, so long as performance requirements for the façade cladding panels are also met. Façade cladding panels must be either non-combustible, low risk / Class 0 or Class 1 depending on country, position on building and location of the building in relation to its ‘relevant’ boundary.

There are several potentially serious issues with this approach.
 

A fit test?

‘Non-combustible’, ‘limited combustibility’, ‘Class 0 / Low Risk’ and ‘Class 1’ classifications of insulation and façade materials are made solely through small scale tests on isolated product samples.

In the case of BS 476-6:1989+A1:2009 (the test used to assess surface spread of flame) the product specimen measures just
225 mm x 225 mm.

This is smaller than a sheet of A4 paper.

The design of the façade system cannot be tested at this scale, and as materials are assessed separately, no consideration is given to how the elements will perform when combined as part of a complete system.
 
This is concerning as even relatively minor design changes — such as the size of gap between façade cladding panels — can have a notable impact on the overall fire performance of a façade system.

Non-combustible?

This route can also allow systems containing large quantities of combustible materials to be deemed automatically compliant.
 
It is possible for composite façade cladding panels with fire resistant outer facings to achieve a Class 0 rating despite containing combustible core materials. In addition, a number of other potentially combustible components – such as vapour barriers, sealants and tapes – may never be considered.

Systems incorporating ‘non-combustible’ insulation in combination with combustible rainscreens have already been shown to fail when tested to BS 8414.

Indeed, during the Department for Community and Local Government’s testing programme, the construction featuring mineral fibre insulation with a polyethylene core ACM failed in under eight minutes.

Full assessment

To ensure proper fire safety in the future, it is vital that much clearer guidance is provided on what materials and systems are appropriate. However, this drive for clarity should not lead to a dumbing down of testing and compliance.

Full system testing provides the most accurate data on how a complete façade system will perform in an actual fire.  As such, it is crucial that the revised Building Regulations and Standards must close off the linear route to compliance and instead ensure that every cladding system is subjected to a system of regulation underpinned by large-scale system testing.

Other articles in this series:

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