Another interum update. One thing I wanted to tackle was the awkward chimney stack and in the end I decided to box it in completely. I made a frame of 2-by-2 and 2-by-4 which is suspended from the skeiling rafters and sits lightly on some foam tape, to minimise vibration and noise transmission from the floating floor:
This frame was then packed solid with RW3 and boxed in with 12.5mm OSB:
I'll be adding bass traps once the room construction is finished, but at least for now that corner is one area I have nothing to worry about when it comes to soundproofing!
I opted to go with the cellotex as insulation in the non-acoustic area under the eaves, as that area is primarily for storage and the cellotex means I don't have to lose space to extra battening. It will be on the other side of a 100mm RW3 insulated wall with acoustic plasterboard on it anyway.
It's not fun to install, as it's non-flexible so has to be cut to exactly the right dimensions to fit between the rafters. I'd been putting this off for ages, partly because I'm simply too big to physically fit in the eave space without serious discomfort.
Mrs. D. is much more sensibly sized however, stepped up to the mark and did the whole lot herself. The image below is only a portion of the installation; the larger storage area alongside the stairs is also lined with it.
I hate multifoil insulation as a material. It's hard to cut, annoying to work with and provides a mushy surface through which it's hard to locate anything, but it has made the room significantly warmer and acts as a vapour barrier, reducing dust from the rockwool. It's also a building regulations requirement so I have no choice but to use it.
The whole space is pretty much covered in it where necessary now:
I've also got some of the resilient bars up ...
... and the first piece of 15mm acoustic plasterboard mounted on them:
The challenge with resilient bars is that they have a fairly tough, if thin, steel surface area to accept the screws holding the plasterboard. As they are so bouncy, it's nigh impossible to get the screw tip to pierce the metal behind the plasterboard.
My solution was to drill small pilot holes through the plasterboard and the resilient bar. This allows the tip of the screws to engage with the metal behind the plasterboard relatively easily and I'll be doing this for all acoustic plasterboarding going forwards.
Finally, I've all but finished plasterboarding (with conventional board) the stairwell and doing the fiddly bits of woodwork associated with boxing in the area above the stairs:
There's still the framing of the doorway at the top of the stairs to do but things are generally moving in the right direction. There's a lot to do but a lot's getting done and I can see light at the end of the tunnel insofar as getting the room construction finished :)