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Yep, I've looked at similar options. Hempcrete is out (mess and weight). I originally assumed cork would be too expensive (perhaps not if unfinished). We already have a base of semi-decent lime plaster and we don't mind working with lime plaster/paints on top.
I contacted Pavatex and they stated that reducing U-values beyond 0.4 was inadvisable as would have too significant effect on rate of drying of the (exterior) wall, hence frost damage. This seems to be confirmed by Jospeh Little in Breaking The Mould:
"It seems reasonable to deduce from this that once driving rain is dealt with internally-insulated walls appear to work best with less insulation than 0.45 W/m2K"
https://www.buildinglifeconsultancy.com/content/breaking-mould-5 (link not secure)However, I wondered if there was an alternative to accepting a worse U-value (for IWI) by reducing humidity (heat recovery from bathrooms for example) as the improved interior environment might provide better external wall performance during dry spells?
Or perhaps I need to fixate less on U-values...
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JonoMarshall
@hoefla
@JonoMarshall - I intend to internally insulate the side wall (end of terrace and don't own the land outside) - I see the breathable, no cavity options as hempcrete (slow, messy and needs thickness to achieve any useful insulation value), woodfibre (needs lime plastering) and cork. They are all humidity buffering to some extent (can take in water vapour and give it out again). I am curious about whether cork can be applied as a thick internal finish (ie no plastering over) or if that leads to issues with condensation behind. Maybe the walls need stripping back to brick and re plastering in lime before adding cork, at which point what's the difference with getting a pro in to do woodfibre. I am currently at the wishful thinking stage of maybe DIY-ing cork but haven't got very far.