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will you be rendering the external to prevent moisture from coming inwards? how did you calculate dew point or did builder?
apc-
The external wall is being raked out and re-pointed with lime mortar (current pointing is cement and largely fucked), then left bare. It's a south-facing wall, so shouldn't ever get soaked through its 230mm thickness.
I used a few calculators to verify wall build-up and dew point etc, like Ubakus and Changeplan.
ectoplasmosis
I'm about to put in interior insulation on a few external walls in our solid-walled Victorian semi, and will likely use PIR instead of wood fibre.
Going by various calculators, the dew point will remain inside the PIR sheet itself, and applying the sheets properly, using foam all round, finishing with airtight tape, will/should prevent moist internal air from ever reaching the brick behind the boards. 50mm PIR will/should perform much better than 60mm wood fibre, and is significantly cheaper to boot.