It's all about energy efficiency. This was a concrete tower block with inadequate insulation and single glazed steel or aluminium windows. To slash heat loss, new external wall insulation and double glazed windows have been a standard solution since the start of the century, and to that extent no problem. EWI on low rise and domestic buildings usually means dark grey PE or Polyethylene foam in blocks up to 150mm thick stuck and screwed onto the existing facade. On low rise this is then usually rendered to give a 15mm thick crust that stops people poking holes in the foam with their fingers (but useless against woodpeckers, who now prefer making nests in EWI than in trees).
We've all known for years that PE foam was a fire risk, and it's always therefore been replaced by 120mm - 200mm of mineral wool for higher buildings. However, repeated wet work - layers of render coats - at heights is costly and problematic, with the risk of injury if the adhesive bond between render and rockwool fails and chunks fall off. In place of render on highrise buildings the industry instead uses rainscreen cladding, designed to be fairly but not absolutely waterproof. So a void is left between the cladding and the rockwool to allow some rainwater to drip down and be drained without soaking the EWI. Again, not a problem if the rainscreen cladding is not inflammable and if fire-stopping and drainage at each storey is incorporated.
What we know from the photographs and news reports is that rockwool was used - correctly - for the insulation but so it seems was the inflammable PE foam - if only in a 5mm thick layer in the middle of an aluminium sandwich for the rainscreen cladding. Suspicions that fire-stopping was left out - which would make drainage behind the facade much cheaper and easier - would explain a chimney effect for the fire spread.
Now, none of this is specialist construction design and engineering. Just about everyone in construction knows the problems with PE foam - and personally I won't even use it for low rise not just because it burns so easily but because it's completely vapour impermeable and stops buildings from breathing - and just about everyone knows the importance of fire stopping between dwellings.
When those responsible for the design and execution of these works face the consequences of their errors it will not be enough to claim that since the government hadn't banned one material or another they are in the clear. All of us in positions of responsibility in construction have an absolute duty of care and design teams - CDM, designer, engineer, supervisor, PM, QS - are constituted in such a way as to provide post-hoc evidence of exactly how such decisions were made. You can be sure that since last Wednesday each one of them will have printed out and assembled every email from this job, every periodic report, every meeting, every bit of written evidence and will now each be constructing a narrative that minimises their own culpability. Lawyers will have been briefed. We must now all wait and allow the enquiry to do what it must.
|Grenfell Tower cladding drawing from Studio E architects|