Improvements in or relating to buildings

With reference to Figure 3, the sloping roof 250 of a building 10 incorporates inner and outer juxtaposed metal panels, 15, 16 spaced from each other to define passageways 20 which serve as heat exchangers. A closed-loop water circulation system 18 connects the passageway 20 with low, medium and high grade heat store chambers 21, 23, 25 disposed within the building foundation structure 13. The water circulation system 18 employs sub-systems 22, 29 and 31 which comprise, respectively, primary, secondary and tertiary sub-systems. The heat store chamber 21 comprises a portion of the primary circulation sub-system 22 whereby water is re-circulated through the panel passageways 20 so as to be raised in temperature by solar neat. In addition to the heat store chamber 21, the primary sub-system 22 comprises a heat pump unit 27. The secondary water circulation sub-system 29 conveys water in a closed loop which, in addition to the heat store chamber 23, comprises the passageways 20 and the heat pump unit 27. The tertiary water sub-system 31 comprises the heat store chamber 25, radiators 19, underfloor heat exchanger coils 35 and a heat exchanger coil 37 incorporated in a hot water cylinder 39. Heat from water flowing in the primary sub-system 22 is given up to the heat store chamber 21 and also to the heat pump unit 27. Heat from water flowing in the secondary sub-system 29 is given up to the heat store chamber 23, as well as to the heat pump unit 27. A controller 40 is operable to provide controlled transfer of heat between the sub-systems 22, 29, 31.