2.3.3 The notional building
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 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 depending on the activity type, and there are particular rules applying to areas of display glazing and doors.
The notional building is assigned standard constructions for external elements – walls, roofs, floors and glazing. A special rule applies to ground floor constructions. 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. There are also rules applying to infiltration rates.
Each space in the Notional building will have the same level of servicing as the equivalent space in the Actual building. In this context, “level of servicing” means the broad category of environmental control, summarised as follows:
a. unheated
b. heated only with natural ventilation
c. heated only with mechanical ventilation
d. air-conditioned
e. mixed-mode, where cooling only operates in peak season to prevent space temperatures exceeding a threshold temperature higher than that normally provided by a full air-conditioning system.
Rooms which in the actual building are served by an Apache System of a given type are assigned the appropriate NCM notional building system in the notional building.
