I'm looking to add insulation (50mm mineral wool or 20mm underlay) below the 1st floor floorboards between the joists. There are access points (floorboards screwed down) in most rooms and, as I live in the house with furniture in the way I don't want to empty the room pre insulating. Ideally I want to thread the insulation between removed floorboards but am not sure how to do this. Can I get some advice?
As above. You're insulating against your own house, waste of time and money and will change literally nothing. If anything, you will make your upstairs colder. Heat rises, and preventing residual heat from downstairs rising may be counter-productive.
Totally agree about the heat issue, however the two occasions it would be useful are: to provide additional sound deadening - nothing more off putting than sitting in the lounge eating when someone decides to use the bathroom above and seconding if there is UFH, where you need it below the pipework to ensure proper transfer and efficiency.
Not here ... I have insulation. However I have been in some modern cheap build houses and you can hear everything. In one flat I know, the residents could tell if the occupier upstairs had been out for curry the night before!
Well I might have lodgers in the future so useful. Also I want to insulate an old Victorian fireplace by putting insulation up the chimney. I have tanked and chemical DPC'ed the fireplace. Should I cover the insulation in plastic first before shoving the insulation up the chimney or leave it bare?
I put 100mm standard loft insulation between joists in a previous house to reduce noise transmission. Coupled with decent underlay, carpet and a plywood deck this was very effective, and would have been even more so if I'd used the more dense 100mm cavity sheets.
Ok but should, as I plan to board out the chimney fireplace and put a TV in the space, insulate the chimney flue with plastic covered insulation?
Yes the fireplace is an opening in the chimney on the ground floor. The ground floor is solid 4" cement (no suspended floor). The chimney runs upward through the 1st floor bedroom (in which there is a blocked off fireplace opening) and up through the loft and out the roof
As long as the chimney is capped I would leave it open and install a small grill on the opening into it on the ground floor.