Many Deficiencies in earlier Building Regulations Before 1994 if double glazing was used –window area could be doubled –requirements for walls/roof/floor could be relaxed if overall loss < = standard house (type 1 trade off) From 1995 –Could include incidental gains from appliance use/solar gains –If consumption <= standard house - regulations could be relaxed further 1994 & 2000 regulations –If triple glazing used window area can be increased by 50% (type 2 trade off) –If higher insulations for walls used, greater window area permitted provided <= standard house.