PE magazine have run the article 'Wiring Timber-Frame Buildings' (a typical construction example shown in the attachment), which seems similar to those alluded to by ES1st (in their BP Guide 5, Fire Safety).
When installing wall fans in timber-framed buildings, one option is to use intumescent sleeving (such as shown in the attachment) for flexible ducting (but seems quite expensive at approx £60 for a standard 100mm ducting up to 500mm). Another option is use non-combustible/metal ducting (as suggested in BPG5). However, does anyone know of a supplier for such metal ducting (fire rated or proven for such use)? When I ask wholesalers and fan manufacturers, they all seem bemused (with some saying they don't think anyone bothers to use them), and as yet a google search reveals little help.
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