In an ‘over-cladding' envelope retrofit, the building is covered with prefabricated insulated panels (see panelized building systems). The approach was refined and put into practice on a mass scale by the Energiesprong program in the Netherlands and later in Europe (see energiesprong.org. The objective is for DERs to be realized quickly on a mass scale, and at a reasonable cost with drastically less inconvenience to inhabitants.