I would like to insulate the space between a downstairs living room and upstairs bedroom. The void is about 7ins deep with the usual mess of electric cables and CH pipes. The upstairs floorboards are and will remain exposed, a limited number of them (previously hacked for plumbing & electrical work) will lift readily. The downstairs ceiling is lath & plaster, not yet underboarded but not yet falling in. Area about 12 m2.
I was thinking of throwing something cheap&cheerfull in to help the thermal insulation [the downstairs room gets through a lot of KwH in the winter, heated to 25C for 8-12 hrs per day, upstairs is unheated]. To this end I thought something like vermiculite would be the easiest (cheapest?, most effective?) as it would run freely to fill the inaccessible spaces. Will any-old e.g. horticultural stuff do or is there a special variety for this purpose - there has been a scare about asbestos being found in some vermiculite?. Or would I be better off using some other loose-fill Rockwool, leaving a 2" gap at the top for ventilation [which sounds harder to do]?.
Or is the most economical thing to not bother!.
Egremont.
PS Sound insulation will help, fire safety is a must!.