My understanding is that the cladding in question, this flammable cladding which is banned in Europe and the US, is also banned here.

Philip Hammond, the UK chancellor of the exchequer, speaking about the Grenfell Tower fire on the BBC’s Andrew Marr show on June 18.

After the devastating fire at Grenfell Tower, the Metropolitan Police is considering whether to bring manslaughter (or other) charges relating to the tower block’s insulation, which it says failed safety tests. The cladding on another 11 high-rise buildings has also failed fire safety tests, according to the communities secretary, Sajid Javid.

Cladding is being added on tower blocks built in the 1960s and 1970s such as Grenfell Tower to improve the thermal performance of the flats and in some cases prevent material deteriorating and falling from the existing facades. These flats are often homes to some of the poorest in society and improving the facades may cut their energy bills to less than a half. This also means that they can adequately heat their homes to avoid condensation and mould growth inside.

The existing buildings have concrete or blockwork walls with a thin layer of insulation on the inner surface. The thermal improvement is achieved with a layer of insulation placed on the outer surface of the existing external wall where it is not impaired by condensation. Because of this, it is necessary to shelter the insulation from the weather. This is done with an outer layer of panels, called the rainscreen. A cavity is left between the insulation and the rainscreen to drain any water that passes joints in the rainscreen.

Fire may spread extensively up the wall if the insulation is combustible, if smoke and flame can travel up the cavity or if the rainscreen is combustible. In practice, fire barriers are placed in the cavity at each storey to prevent the movement of smoke and flame and separate the insulation into storey-height portions. This limits any spread of fire through the insulation which should be of limited combustibility in high rise buildings.

Many materials have been used for rainscreens in the UK, ranging from lightweight metal panels, through composite boards and terracotta to natural stone on upmarket city offices. Aluminium composite materials (ACM) are used as a lightweight economical solution that can be readily formed into different shapes with different surface finishes.

ACM comprises two metal skins (normally of aluminium) bonded on to a core of sheet material. Manufacturers make three grades of these material: polyethylene core (PE), which has the worst performance in fires and has been linked to major fires in other countries, and two higher-performance grades of material (FR and A2) which are based on cores with a mineral content and perform better in fires.

A polyethylene core will melt and catch fire, burning rapidly with a heat output in excess of 125 MJ/m2 – similar to the effect of burning an equivalent volume of diesel fuel. A fire will then spread rapidly up the façade while burning droplets may fall from the building and spread fire downwards. The loss of the rainscreen in a fire makes the fire barriers in the cavity ineffective and the insulation is more likely to burn and contribute to the fire spread.

Author provided

What the regulations say

Building Regulation part B in England requires that all insulation and filler materials – a term that is not defined – in the wall of a high-rise building are of limited combustibility. The ACM panels do not fulfil the role of insulation and have no particular insulative properties. It is commonly argued, then, that they are not fillers. This confusion and the resulting loophole in the regulations mean that polyethylene core ACMs have been used on high-rise buildings ostensibly in compliance with Building Regulation B, as is the case at Grenfell Tower.

Approved Document 7 of the Building Regulations requires that: “Materials are of a suitable nature and quality in relation to the purposes and conditions of their use.” This fitness-for-purpose is not well defined in the regulations. However, the manufacturers of ACM state that the PE version is not suitable for use above ten to 15 metres on a building because of its fire risk and also make mineral core alternatives that are suitable.

Regulations differ from country to country, even across Europe to the extent that building regulations in Scotland differ from those in England. European cladding consultants have expressed concern to me about the use of these materials in their countries.

Verdict

Hammond’s claim that the type of cladding used on Grenfell Tower is banned in the UK is nearly correct because of the less well-known Approved Document 7. But neither this document, nor Building Regulation B specifically bans the use of PE core ACM panels.

Review

Masi Farjadmand, senior lecturer, Department of Property and Construction, University of Westminster

This article contains certain amount of information from publicly available materials which are generally correct. I have no specific objections to the opinions expressed in it and the verdict is accurate. Vertical spread of fire from outside a building is a result of many factors. The material used for cladding and its combustibility is only one. The gap allowing the fire to move from one storey to the next, mostly upwards and sometimes down, is an important factor.

Approved Documents 7 and another British Standard Online document – BS 8000-6 – a code of practice for slating and tiling of roofs and claddings – provide general guidelines, as do all other standards. The cladding used for Grenfell Tower is not illegal to the letter of the law, but it may not comply to the spirit of either the law or the regulations. This will be a matter for investigators to determine. In the case of Grenfell Tower, many aspects of fire safety and fire engineering contributed to the spread of fire and the cladding is only one of them.