This technical note applies to cases of renovation without demolition, when the old layer structure can be maintained in place. Demolition of the existing layer structure, should, for both economic and environmental reasons, be the last solution to be considered! Full demolition should only be considered in the presence of a layer structure that includes fibrous thermal insulation which is disintegrating and heavily impregnated with water. Deferring demolition works and the consequent reduction in waste over time that results from this is a fundamental criterion of sustainable building. The disposal of waste, and the costs of this, are increasingly problematic, and so it makes sense to avoid the full demolition of the old layer structure.