Last edited 14 Aug 2017

Building envelope

According to Approved Document L2B: conservation of fuel and power in existing buildings other than dwellings, the term 'building envelope' refers to:

...the walls, floor, roof, windows, doors, roof windows and roof lights.

Together, these form the physical separation between the interior and exterior, that is, the climatic modifier that creates and contains the internal conditions.

The nature of the building envelope is likely to depend on a wide range of requirements, some of which may be in conflict:

  • The type of building.
  • Its location and context.
  • Its form.
  • Regulatory requirements.
  • Local climatic conditions.
  • The internal conditions required.
  • The need for openings, views, security, safety, access, privacy and so on.
  • Available materials.
  • Structural requirements.
  • Building services strategy,
  • Sustainability requirements.
  • Maintenance and cleaning requirements.
  • Rainwater run off.
  • Durability, flexibility and expected life.
  • The method of construction, deconstructability and recyclability.
  • Stylistic requirements.
  • Budgetary and time constraints.

NB According to Approved Document L1A:

The envelope area of a terraced house includes the party wall(s). The envelope area of a flat in a mulit-storey building includes the floors, walls and ceilings which are shared with adjacent flats.

And, in relation to air permeability:

The envelope area, or measured part of the building, is the total area of all floors, walls and ceilings bordering the internal volume that is the subject of the 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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