Envelope area
Approved document L, Conservation of Fuel and Power, Volume 2: Buildings other than dwellings, 2021 edition incorporating 2023 amendments, defines the building envelope (in relation to a building) as: ‘Defined in regulation 35 as the walls, floor, roof, windows, doors, roof windows and rooflights.’
It defines the envelope area as: ‘(the measured part of the building) The total area of all floors, walls and ceilings bordering the internal volume that is the subject of a pressure test. This includes walls and floors below external ground level. Overall internal dimensions are used to calculate this envelope area, and no subtractions are made for the area of the junctions of internal walls, floors and ceilings with exterior walls, floors and ceilings.’
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