Comment Re:Multiple issues .... (Score 1) 82
Internal wall insulation is relatively straightforward and retrofitting in older housing with single-skin brick walls similarly so.
For example:
https://www.celticsustainables...
https://www.smartstoneenergy.c...
Do the calcs, do not overloook your air movement and general ventilation requirements, and favour natural materials. Gypsum-based plasters are not typically breathable so may need to be removed from internal walls.
External insulation may be better, less disruptive to install but requires an immediate investment rather than a room-at-a-time for internal insulation. YMMV.