I can see the horrific charcoal skeleton of Grenfell Tower from my office window. I cycle past the tower every day and my heart sinks when I glance at the blackened shell of it now. My thoughts are with all of those who were killed, and to those who have lost everything and now have to rebuild their lives.
The external insulation at Grenfell Tower
I work in energy efficient building design, but this research was done in my own time. I’ve been reading everything I can about the refurbishment that took place to improve the thermal performance of the tower block. I do not intend to pass judgement on any element of this awful tragedy, but I thought it would be acceptable to collate the information I’ve found on the cladding insulation in one blog-post.
The investigation will ultimately discover what happened, and I hope that it will serve to prompt significant and permanent changes in future fire safety for high-rise structures in the UK.
The insulation and the external cladding – fire resistant, rain screen or both?
A renowned building physics consultancy produced the Grenfell Tower Regeneration Project Sustainability and Energy Statement Planning Application ahead of the renovation project in 2012. I would like to highlight a couple of key points related to fire safety from that application.
On the topic of updating the heating system:
The existing heating pipework may not be in an acceptable condition to be retained. New central pipework would need to be installed within all six service risers. This would involve partially removing the fire stopping between floors and replacing it after the new pipework was installed.
Partially removing the fire stopping between floors makes sense – how else do you remove old copper pipes that run through these fire barriers? But was the fire stopping reinstated properly? And should residents have been moved out during this period?
It should be noted, the document is referring to internal fire stopping in the service risers, and not anything to do with the external cladding.
On the potential external cladding:
The planning application also offers up a potential external cladding material build-up to improve the thermal performance of the exterior walls. From outside to inside, that build-up was to be:
Zink (sic) Cladding (New Rain Screen)
A ventilated cavity
Insulation (New, Celotex FR5000)
Cast Concrete (Existing)
So it suggests “Celotex FR5000” be used.
But a Guardian report suggests that Celotex RS5000 was actually installed as the insulation panel within the cladding system.
The specifications sheets for each type imply a few key differences between FR5000 and RS5000.
On the Saint-Gobain website it notes that Celotex RS5000:
- has been tested to BS 8414-2:2005, meets the requirements in BR 135 and the first PIR insulation suitable for rainscreen cladding applications above 18 metres in height
- features Class O fire performance
Celotex FR5000 does not mention anything on its product page about being used on buildings above a certain height, but the “FR” would seem to indicate “Fire Resistance”. “RS” would seem to refer to the “Rain Screen” performance of the insulation panel. I’m inferring this – I don’t actually know what they stand for.
The spec sheet from Celotex indicates how the fire resistance of RS5000 was tested to meet BR135, which is the UK Building Regulations section that deals with “Fire performance of external thermal insulation for walls of multi storey buildings”.
I don’t have the rights to re-print the diagram which shows how external cladding can contribute to flame spread, but you can imagine that it’s as we saw on the news – flames lick from windows, super-heat the panels around them, which reach a smouldering point and catch fire. This sets off a chain reaction and the fire rapidly creeps up the building, quickening its momentum as more cladding is caught in the flames.
Were floor-by-floor fire barriers integrated into the cladding or insulation?
From the Celotex document:
Failure to meet the performance criteria set out in BR 135 is deemed to occur if the system:
- Records temperatures exceeding 600° C for a period of at least 30 seconds within 15 minutes of the start time at level two external thermocouples
But it highlights that, under fire test conditions, they used fire stopping made up of mineral wool insulation – so this would have to have been designed into the real-life scenario at Grenfell in order for the insulation or rainscreen cladding to not contribute to fire spread.
Again, in the test conditions:
Fire stopping was provided by ventilated horizontal fire breaks positioned at each floor slab edge and above the hearth opening. Vertical non-ventilated fire breaks were provided at the edges of both the main face and the return wing and around the hearth opening.
In the test conditions, these fire barriers were comprised of:
Stonewool insulation with Class O aluminium foil facings and a continuous bonded intumescent strip. Non-ventilated fire barriers comprised of stonewool insulation with Class O aluminium foil facings specifically intended to fully fill the void.
Did Grenfell have these mineral wool fire breaks on every floor?
Ultimately, I’m only drawing this information from the publicly-available information on the internet. I don’t know if either RS5000 or FR5000 were the insulation used for the Grenfell refurbishment – maybe they chose something else in the end. It’s not clear how the rainscreen cladding was fire stopped, if it was this material that caught fire.
Whatever caused the fire to spread so rapidly, let’s hope it’s permanently designed out of buildings – so that this tragedy never happens again.
Edit (21.06.2017): Please see more information from a commenter below.