BS ISO 9836:2011

1   Scope This International Standard deals with the definition and calculation of surface area and volume indicators . In defining area measurement, this International Standard uses three measurement concepts:

a) the intra-muros and extra-muros concept used in many parts of the world;

b) the wall centre method of measurement used in many parts of the world;

c) variations on these methods to comply with certain national laws, or for particular types of buildings.

The surface area and  volume indicators  defined in this International Standard are intended for practical use, as a basis
  for measuring various aspects of the performance of buildings or as a planning aid.
  In other words, they should enable judgement to be made on functional, technical and
  economic aspects of buildings. 
This International Standard is intended to be used when establishing: 

   
      
         

— specifications for the geometric performance of a building and its spaces (e.g. in design, purchasing procedures, etc., or in building regulations where appropriate);

— technical documentation relating to the...