Envelope Area Definition

Envelope area – the total area of all wall, floor and ceiling elements that enclose the internal volume subject to an air permeability test. This includes walls and floors below external ground level. Overall internal dimensions are used to calculate this area. No subtractions are made for the area at junctions of internal elements (partitions and intermediate floors) with external elements (exterior walls, floors and ceilings). The envelope area of a terraced building includes the party walls. The envelope area of a flat in a multiple storey building includes the floors, walls and ceilings that are shared with adjacent flats.