Apparatus for recovering thermal energy escaping through a wall structure. The apparatus comprising a wall structure (2) provided with a thermal energy recovery layer, the thermal energy recovery layer having an arrangement of one or more air breathable sections provided adjacent one or more non-air breathable sections. Rising or falling air (3) at an outer surface of the wall structure (2) passes over the one or more non-air breathable sections to collect escaping hot or cold thermal energy before passing through the one or more breathable sections to thereby be recovered. Further provided is an air collection means (4) for collecting warmed air rising up or cold air flowing down an external wall of said building. The air collection means comprising a tapering converging guide member extending outwardly from the building's wall (2) for collecting and directing rising or falling air into the building.