I'm in the process of boarding out some attic rooms in a Victorian terrace. I'm going into the alcoves either side of the chimneys. At floor level, the chimney stacks seem to have been built with a form of cavity. Presumably this was to isolate the timber from the heat of the chimney stack?
Here's a pic*:
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I don't intend to use the chimneys without having them lined - but that's a long way off.
Anyway, I'd like to block these cavities to limit the amount of sound that travels between neighbours. I was thinking of using some fire grade expanding foam. Or is this a bad idea?