The dwelling boundary or thermal envelope consists of all building elements separating the dwelling from the external environment, adjacent buildings, and unheated spaces. Except where otherwise indicated, linear measurements for the calculation of wall, roof and floor areas and dwelling volume should be taken between the finished internal faces of the external building elements. Space occupied by internal elements (internal partition walls or intermediate floors) is considered to be part of the total dwelling volume. Measurements for the calculation of the areas of external door, window and rooflight openings should be taken between internal faces of sills, lintels and reveals. ’Volume‘ means the total volume enclosed by all enclosing elements and includes the volume of non-usable spaces such as ducts, stairwells, and floor voids in intermediate floors.
Dimensions
Refer to the inner surfaces of the elements bounding the dwelling. Thus, floor dimensions are obtained by measuring between the inner surfaces of the external or party walls, disregarding the presence of any internal walls.
Further guidance on floor area and unheated spaces is set out in the following sections.