The notional building is derived automatically from the actual building according to rules laid down in the NCM methodology. These rules are set out in full in the official documents and what follows is a summary.
The notional building settings represent standards of construction and system efficiency that are similar to those applying in the Elemental Method of Part L2 (2002).
The location and geometry of the notional building (with the exception of glazing and door area) are copied from those of the actual building:
Glazing in the notional building is modified to conform to standard facade area percentages depending on the building type, and there are particular rules applying to areas of display glazing, doors (of two kinds) and smoke vents.
The notional building is assigned standard constructions for external elements – walls, roofs, floors and glazing. A special rule applies to ground floor constructions. In broad terms the notional building constructions conform to the standards of the 2002 regulations. Where the actual building has spaces that are designated ‘Unheated roof’, ‘Unheated buffer space’ or ‘Glazing cavity’ – indicating spaces that form part of the building envelope rather than the occupied areas – these spaces are absorbed into the elements by which they connect to the occupied areas in the notional building, which are assigned the appropriate standard constructions.
Rooms in the notional building are assigned the same NCM Templates as their counterparts in the actual building, so that the occupancy, gain and plant operation regime in each room conforms to the appropriate NCM Activity.
In the notional building, room data that is not covered by the NCM Activity (and which in the actual building is set by means of the Room Template) is also set by the NCM Template, which in respect of these attributes contains the data stipulated in the official notional building definition. In particular, infiltration rates are set in conformance with the Part L2 (2006) standards of air-tightness as interpreted by BRE TM 23.
Three types of systems may be present in the notional building, depending on the type of room conditioning used in the actual building:
Heating and natural ventilation,
Heating and mechanical ventilation, or
Air conditioning
For each type of system, standard efficiency characteristics are laid down in the official notional building definition. In <VE> Compliance, the three types of system appear as Apache Systems named
NCM notional heating + nat vent system
NCM notional heating + mech vent system
NCM notional air conditioning system
Rooms which in the actual building are served by an Apache System of a given type (as indicated by the ‘Cooling mechanism’ setting) are assigned the appropriate NCM notional building system in the notional building.
