If you enjoyed the Inside Housing reporting on the history of Approved Document B that led to Grenfell materials being possible, here's a brief summary of the AD B changes that led to the confusion on height regarding The Cube fire in Bolton ...

#boltonfire

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The change in AD B introduced in 2006 to allow combustible insulation at height via the BS8414 testing route has been beautifully documented by Inside Housing. The changes regarding height go back a bit further, but are easier to understand than the rules themselves ...

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Changes made in 1992 arguably allowed combustible materials to be used to an even larger extent than the changes in 2006 ...

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In 1985 life was relatively simple. There was one height measurement rule (the building height), and it covered all materials in an external wall ...

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As has always been the case, there was no requirement for cladding even then to be limited combustibility, despite what @mhclg claimed in the days after Grenfell …

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However, in Approved Document B 1992, things all get a bit messy:

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A.The ‘building height’ threshold moves from 15m to 20m (no sign of the precious 18m anywhere)

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http://B.Limited  combustibility insulation gets its own, new height threshold of “a storey at more than 20m” which is roughly equivalent of a ‘Building height’ of at least 23m (around 9 storeys).

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C.The split definition leaves the reaction to fire requirements of other external wall materials (covered by 1985 4.7) undefined, such as cladding mounting components, sheathing boards and membranes (which almost don’t exist at the time).

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The increase in height criteria from 15m to 20m is an obvious step backwards for fire safety, and so is the uncertainty created for other materials.

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But WHY??? was a second method of height measurement introduced that so confusingly complicates matters?

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The condition that you must have a ‘storey’ at height means that if it isn’t 'residential', then basically you can use combustible insulation no matter how high the building, whereas before with any building over 15m it was prohibited.

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So commercial buildings, leisure centres, distribution/warehousing etc becomes an almost unrestricted market for combustible insulation products in 1992.

Brilliantly, and quietly done.

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