There’s a lot of bollox being reported about Grenfell cladding, its spec changes and “100%” failures on every other tower block cladding sample tested.
Purely anecdotal quickie – my opinions as an engineer – I have no inside knowledge on these tower block refurbishments
Pretty sure the “zinc” will have been some galvanised or zinc-coated steel. Heavier than aluminium, and less flexible in terms of possible finish appearance coatings. And, the claddings in question are entirely about aesthetic finish. Freshening-up the look of the ageing blocks.
Secondly I’d bet the saving here is in the “cassette” approach to modular fixing. Simpler and lighter weight fixings for lighter panels. Anecdotally in various media news film of cladding removal and inspection work, there has been enormous variation in the cladding SYSTEMS. Those like Grenfell seemed to have been as crude as (vertical) timber battens nailed into the old concrete with the cladding sandwich pinned onto these battens with a chimney airspace behind. No insulation, no convection-breaks. Others had both insulation and pre-formed (horizontal and vertical) metal supports. I’m sure there are many other system variations.
The cladding itself is a sandwich, pretty sure the price-per-sheet variation of the material (skin and core) has little to do with the material cost, more to do with the manufacturing and supply chain.
Nothing in these (strongly encouraged, always) value-engineering bid proposals – NOTHING – will have relaxed the actual regulations and specification required to be met.
Much of the testing appears to have been on the sandwich core material (as reported on @BBCR4Today today). There are several levels of SYSTEM being ignored here. The sandwich itself is more than the core, and the skins are variable too. The installation varies in terms of insulation, fixings, convection-breaks, geometric arrangements and more …
Pretty sure the BRE testing of just the core has simply been a conservative agreement to compare apples with apples, removing all the other variables for simpler testing interpretation. PE core is flammable, even with retardant fillers – no surprise, same result everywhere. True, but close to useless, like most simplistications.
Let’s stop rushing to judgement and let’s stop publishing half-baked stories to confuse a wider public.
I am not alone:
— DaveHillOnLondon (@DaveHill) June 27, 2017