As you might expect, we have had a huge number of calls and emails over the last couple of days regarding external wall insulation. It was with great sadness that we all witnessed the events at Grenfell Tower, in North West London – our deepest sympathies are with all those involved.
It is clear that much of the media have already begun to blame the rainscreen cladding system as a contributing factor to the accelerated pread of the fire. Obviously, a full investigation will have to take place before we know for sure, but it certainly looks like this may have been the case.
We feel it is important to educate people on this type of cladding system. Rainscreen cladding is a solution that is primarily designed to protect a building from the elements. It tends to be made up of a protective, decorative outer coat attached to the underlying structure of the building by a supporting grid (metal frame in many cases). The cavity created between the outer cladding and the building structure is often used to house insulation materials, but also it maintains a ventilated cavity, and aids draining. The cavity between the insulation and the protective cladding is normally a minimum of 25mm.
These rainscreen cladding systems can be either retrofitted to existing buildings or incorporated into new builds.
Often rainscreen systems are hybrid systems based on architects’ requirements to improve both the look and thermal performance of a building. They therefore take advantage of materials from different companies to provide the desired effect.
External Wall Insulation (EWI) is not rainscreen cladding
External wall insulation on properties is very different – in the majority of cases this is retrofitted to the property to improve the thermal performance of the property while also giving it an aesthetic facelift. The materials used in external wall insulation are specifically designed to work together to produce the desired effect – they normally all come from the same manufacturer.
Basically, an insulation board is ‘glued’ to the wall using cement based plaster adhesive. Mechanical fixings then tie the insulation board to the wall. On top of this another layer of cement based plaster is added and a fibreglass mesh is sunk into the plaster while it is still wet. Finally, a top coat render is added to the system to give the desired finish – this can be any colour and also comes in a huge range of different finishes. Our understanding from speaking with a few external wall insulation manufacturers is that the insulation material is fulling enclosed within base rails and the cement based finish from the external elevation of the property.
External Wall Insulation is a regulated market
The external wall insulation industry is a heavily regulated industry in the UK. Independent bodies such as the British Board of Agrement (BBA) and KIWA-BDA are notified bodies and UKAS approved to independently test and certify external wall insulation systems so they meet the rigours of the building regulations here in the UK. As part of this independent testing, the systems are tested against a number of elements including: water absorption, wind loading and combustibility.
Independent certification of the manufacturers and their internal processes around the system’s design – whether this is through specifications, profile drawings and site-specific engineering calculations – makes the planning stage pretty comprehensive.
In addition to the manufacturers or system designers, the installers themselves doing the works may also be accredited with the PAS2030 or an equivalent quality management system. While these certification and procedural elements don’t necessarily guarantee the quality of the final installation, you can rest assured that those installers will be monitored and rigorously audited on the works that they do. Monitoring bodies who enforce the PAS2030 certification have the power to kick off bad installers to keep the standards in the industry high.
Finally, it is also worth mentioning that on bigger projects, like a retrofit of multi-storey properties or a number of properties within an area, the system designers will also send their technical teams to provide additional monitoring of the installers to make sure they are getting installed as they have been designed on the system specification and the BBA certificate. The installers themselves should also (via the manufacturers) provide maintenance advice post installation that helps maintain the system safely and securely during its lifespan.
Mineral wool and stone wool are classified as non-combustible
The insulation material itself tends to be either made from mineral wool or EPS. Mineral wool offers substantial protection against fire since it is non-combustible (Euroclass A1). Regardless it is enclosed within a layer of concrete adhesive, so the structural integrity of the system would remain intact even if there was a fire.
With regards to EPS, it is an organic compound so it would burn in much the same way as wood or paper if fire came into contact with it (it would actually melt first). In the case of EPS used in external wall systems, it tends to include a flame retardant such as polymerised bromide to help decrease its flammability.
EPS is fully enclosed within the external wall finish
If there was a fire in the property, EPS would melt within its cement-based plaster enclosure, but the mechanical fixings would support and hold the structure of the EWI in place. So, while after the fire, an EPS external wall insulation would need to be stripped and replaced it should not act as a fire accelerator.
External Wall Insulation industry post-2017
As mentioned we are extremely saddened by the events at Greenfell Tower, but we feel it is important the mainstream media do not scare the hundreds of thousands of people who have had solid wall insulation installed on their properties over the last few years. Therefore, we must allow the independent enquiry to take place, which will allow the evidence to be gathered and hopefully form conclusions about this incident, leading to even more robust standards in future across the building industry.