Heat Insulation NEUTRALUX A new Energy Saving Directive (EnEV) has replaced the former Heat Insulation Directive from 1995. The new directive contains even stricter stipulations for heat insulation. The average U value (unit of heat loss) of a building structure must now lie between 1.05 and 0.44 W/m²K for residential housing with a maximum 30% proportion of window area. For non-residential buildings with minimum 30% window area, the U value required is between 1.55 and 0.58 W/m²K. Application NEUTRALUX can be used in all types of buildings, and offers both optimum heat insulation and high light permeability. Energy is gained passively from sunlight passing through the glazing units. The glazed areas are also highly light-permeable.