Why is it so important to renovate old buildings?

Both historic buildings and the building stock from the 1930s to the 1970s are known to be real energy guzzlers. Walls, windows, roof and cellar are barely or not at all insulated or sealed, and thus provide no heat and sound protection. Outdated heating systems also consume much more energy than necessary, due to two factors: actual heating and high electricity consumption.

On the left: nineteenth-century villa before renovation (source: GrAT); on the right: housing complex in Linz, Austria, before renovation (source: Domenig-Meisinger/Willensdorfer 2007)