Ceilings and basement
Ceilings to be insulated during a retrofit process are either cellar ceilings or the ceiling to an unheated attic. If heated zones are adjoining unheated parts such as cellars or the ground it is energy-saving to improve the thermal resistance of those walls ceilings and slabs, too. However the post insulation of basement slabs and walls to the ground is often complicated and rather expensive.Post insulation of floors is often done for comfort reasons to obtain higher floor temperatures and avoid draughts along the floor. A weak point to which special attention is required is the floor/wall connection for buildings with slab-on-ground constructions. The temperature difference between for example unheated cellars and the heated part of the building or between the ground and the heated zones is about half as high regarded over the year than from building parts to the ambient. This results in a bisection of the specific transmission losses and therefore in a smaller efficiency of insulation

measures. Hence the insulation thickness of these building components should be regarded under particular economic and constructive views.Cellar ceilings are often thermally retrofitted by mounting insulation on the lower surface, sometimes there are covered by gypsum boards or wood fibre boards. If fire regulations have to be considered, the insulation material is mostly mineral wool.Ceilings to an unheated attic are usually insulated by using polystyrene boards on top of the ceiling, sometimes covered by a wooden sheet to walk on. This work can be easily done by pupils being supervised by a care-taker or teacher with some practical experience and is therefore a rather economic way of improving the thermal quality of the building envelope.If walls to unheated zones are going to be retrofitted this should be prefarably done at the exterior (cold) side, if not possible as often in case of walls to the ground it may be done on the inside including the use of a vapour barrier.