Hello. I am currently converting my loft (1940's house) and am struggling to find the required information about insulating / fire-protection for my brick chimney stack as it passes through the extension. I can't see an applicable insulation u-value (is it an external wall or internal wall?) and am not sure whether chimneys have to be clad for fire regs as I've seen many pics of exposed chimneys within conversions?
The chimney is free-standing within the habitable loft space. It has two flues - one is closed off and the other has a twin wall flue (professionally installed about 5yrs ago) from the log-burner in our lounge, which we use once per week or so in winter. As far as I'm aware, the outer wall of the chimney doesn't get hot when in use and we have no intention of ever using the flue for an open fire. I am intending on using metal studs, attached to the brickwork and then would like to use the smallest depth pir insulation / air gap possible to comply with insulation/fire regs, as the space is quite tight on one side of the chimney. Do I need an air gap if using pir and creating a vapor barrier, can the insulation go between the metal studs and what plasterboard should I screw to the studs (Its small enough to use a single sheet on each side). Ideally I want to add a maximum of between 5-10cms to the chimney dimensions on the affected side. I will be getting a building inspector in to check but want to get all of the studwork up in advance. Thanks for your help.
