Partitions & Ceilings - gypsum & rockwool V's natural alternatives

[DamoKernow]

Hi there,

I'd really appreciate some advice regarding the choices involved in partition walls, between floors and ceiling linings - choosing between gypsum products and Rockwool type insulation batts over a wood wool fibre board and lime - specifically relating to vapour permeability and summer insulation. Phew!

Background
We are renovating our granite property and keeping the envelope vapour permeable; we've already lime pointed externally (and added Storm dry) and will be adding IWI (Steico wet) to all externally facing walls, which will be rendered and plastered with lime.
We have a party wall encompassing about 1/3 of the envelope walls which will be lime rendered (i.e. not have the IWI system).
We have also fitted a new slate, vented, warm roof, using wood fibre sarking and insulation batts (Steico). A VCL has been fitted. We are at the stage of lining the ceiling.
Other information that may be useful:
Geocell and limecrete floor.
Heating provided via Wet UFH throughout the ground floor area, + rads and woodburners.
Ventilation via PIV.


Concerns
Other than the obvious environmental impact of using gypsum products, and the potential cracking of skim, the other downfalls I can think of by using Gypsum over natural products involve:
1: Losing out on vapour permeability - I have read on several occasions that both gypsum plasterboard and One coat plaster are vapour permeable. I don't know how they compare to a wood wool fibre board (e.g. celenit or savolit) and lime plaster system.
2: Not being able to maintain a cool home in summer. Assuming that gypsum is vapour permeable, how much benefit will we gain in keeping the rooms cool in summer from choosing natural insulation batts (e.g. wood fibre or wool) over a glasswool/rockwool type batt? That is, I understand that natural insulation is more effective in absorbing heat (compared to glass or rock wool), but how much benefit will we gain via the partition walls and between the floor?
3: Anything else I'm missing?


Choices
Cost is currently a driving factor. Therefore as opposed to using the wood fibre boards and a lime plaster system, we are considering using:
a) Plasterboard and One coat (as we want to achieve a rustic finish) between partition walls, and on the ceilings (I would assume we would need breathable paints?)
b) Lime wash direct onto plasterboard (e.g. primer + prep-coat + lime wash from Bauwerk)
c) Rock wool type insulation batts between partition walls, and between the 1st floor.
d) Any other suggestions?


Many thanks in advance!
Damian

 

[a twig]

If you’re using gypsum based plaster board then no benefit of using anything more breathable than emulsion to be honest.

Lime washing gypsum won’t provide any breathability benefits and won’t easily match the finish of lime based walls due to texture.

Earthborn clay paint was the only way I managed to “match” lime and gypsum finishes.

Ultimately if it’s a partition wall (and particularly if it is a stud wall) then breathability doesn’t really matter as much, so choose as best suits your wallet / desired finish

 

[DamoKernow]

If you’re using gypsum based plaster board then no benefit of using anything more breathable than emulsion to be honest.

Lime washing gypsum won’t provide any breathability benefits and won’t easily match the finish of lime based walls due to texture.

Earthborn clay paint was the only way I managed to “match” lime and gypsum finishes.

Ultimately if it’s a partition wall (and particularly if it is a stud wall) then breathability doesn’t really matter as much, so choose as best suits your wallet / desired finish

Thanks for the advice "a twig". All noted thank you.

 

[Zebra]

It sounds like a wonderfully well thought out system. I would not want to compromise a fully breathable system like that by using plasterboard on external walls or top floor ceilings, although it is breathable to an extent... just seems to go against what you're trying to achieve.

But on internal walls and ceilings between floors there's no drawbacks to plasterboard other than that of matching the appearance, and no drawbacks to rockwool batts.