Neither is automatically best. Internal insulation affects room space and finishes; external insulation changes the outside of the building. Both need careful detailing around openings and junctions, and a plan for moisture. Ask how existing defects will be repaired and what permissions or specialist advice are needed. Compare disruption and the full scope, not just the price per square metre.
Join the discussion: Is preserving the exterior, keeping room space or limiting disruption your main concern?
Suggested next step: Compare a whole-property assessment of internal and external options.
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