Since the mid 70's, the construction industry has made significant advances in energy conservation and improved indoor conditions. These improvements, however, are shadowed  by an increase in building envelope problems to include water penetration, condensation on and in roofs and exterior walls and cladding damages in many of our newer buildings; These problems have been attributed to uncontrolled air leakage.

The Jandel school in southern Sweden was thoroughly retrofitted in 1994-95. Both lighting and ventilation systems have been designed for high energy efficiency. New windows with excellent insulating performance have been installed. A before and after comparison shows that the energy required for heating has been reduced from about 210 k Wh/m2 to about 94 k Whlm2 a year, i.e. a reduction of about 55%. Electricity for building services systems has decreased by about 20%, despite the fact that considerably more computers are used in the school today than prior to rebuilding.

Grilningen primary school near Zurich, Switzerland, was built 20 years ago, and energy consumption, in particular for heating and lighting, was unnecessarily high. An unconventional retrofitting procedure involving new chip-wood furnace, interior insulation, mass-coupled ventilation and controlled artificial lighting was adopted. The work was carried out without interruption of normal school operation. The results are very promising and measurements indicate a drop in heat consumption of 70% with standards of comfort raised considerably.