The world is not black and white, but a shade of gray. We have experience with subsequent insulation on three properties. First, a daycare center built in 1963. Sand-lime brick faced, air gap, single glazed. ETICS applied, mold problems in one group room, cause thermal bridge to the roof, after upgrading the roof insulation the problem was solved. Secondly, a residential building from 1969, construction like the daycare center. ETICS, old wooden windows retained, only double glazed, no problems. Thirdly, a multipurpose building from 1979. Poroton brick faced. Different concept. All wooden windows triple glazed with added layers, new rubber seals, perlite blown into the air gap. No problems. Heating cost savings around 25% for all properties. It was right to keep the wooden windows, as they were intact, since they are not so airtight. Living or room climate pleasant, maximum heating cost savings not achieved, but mold avoided. Karsten