Building types
The building must be assigned a type for the purposes of Part L, for example ‘Office’. This affects the methods available for showing compliance and the requirements that must be met.
Rooms to be included in the analysis
Analysis is carried out for all rooms for which the box ‘Include room in Part L analysis?’ is ticked. Other rooms, including rooms in inactive layers, may play a part in the analysis by providing boundary conditions for rooms that are included: if such a room is adjacent to an included room, there is assumed to be no heat loss through the partition.
By including only certain rooms it is possible to perform Part L analysis on part of a building or a building that forms part of a multi-building model.
Room types
Each included room must be assigned a type indicating whether it is heated and whether it falls into any special category such as ‘Room in the roof as material alteration’ or ‘Glazing cavity’.
Unheated rooms (those of type ‘Unheated space with pitched roof and insulation between rafters’, ‘Unheated space with pitched roof and insulation between joists’, ‘Glazing cavity’ and ‘Unheated space or space with low level (<= 25W/m2) of heating’) feature in the analysis as pathways for heat loss from heated rooms (see ADL2 paragraph 0.12). Such rooms must be assigned a ventilation rate to allow the heat loss calculation to be performed by the method set out in BS EN ISO 13789:1999[7].
Rooms that do not have controlled heating but are nonetheless heated incidentally should be assigned the type ‘Heated space’. Examples of rooms in this category are plant rooms, lift-wells, untreated store rooms, and ceiling voids.
Unheated rooms
Partitions between heated rooms and unheated rooms (‘link-exposed elements’) are treated as heat-loss elements with a U-value derived from a generalisation of the transmission heat loss coefficient calculation method[7]. This generalisation extends the method to cover the case of unheated rooms that have adjacencies to more than one heated room. A heat loss network is solved to obtain transmission heat loss coefficients from each heated room to the outside via the unheated room or rooms. Where there is only one adjacent heated room (the most common case in practice) the method is equivalent to the transmission heat loss coefficient method.
An exception to this rule is applied where an unheated room has no conduction heat loss path to the outside, either directly or via other unheated rooms. In this case partitions between the room and adjacent heated rooms are treated as internal elements.
Basis for calculating areas
In accordance with ADL2 paragraph 0.19, element areas used in the Part L calculations are measured between finished internal faces of the external elements of the building. These areas are calculated automatically from the building geometry and the element thicknesses as defined in APcdb, on the assumption that the ‘inner volume’ representation is used in ModelIT.
Because the Part L uses a different area convention from other Virtual Environment applications, areas used by the Part L software will not exactly match those displayed in ModelIT and Apache.
The figure for ‘Floor area (heated rooms)’ displayed at the top of the Part L results file is total internal floor area summed over heated rooms, excluding those of less than 1.5m height (for example ceiling voids).
Basis for calculating U-values
As required by ADL2 paragraph 0.15, U-values are defined in accordance with the conventions set out in the appropriate BS EN ISO standards. The APcdb interface displays both CIBSE and BS EN ISO U-values.
When creating constructions in APcdb, allowance should be made for the effects of heat bridging and the geometry of ground floors. These features are currently not catered for in the APcdb interface, but are scheduled for inclusion in the near future.
Glossary
The following terms are used in this manual:
Element - a wall, partition, ceiling, roof, floor, door, window or rooflight.
Opening - a door, window or rooflight.
Non-opening element - a wall, partition, ceiling, roof or floor.
Glazing opening - a window or rooflight.
Environment-exposed element - an element exposed to the external environment.
Link-exposed element - an element linking to the external environment or the ground via one or more unheated spaces.
Exposed element - an environment-exposed or link-exposed element.
Earth-contact element - an element in contact with the ground.
Heat-loss element - an exposed or earth-contact element bounding a heated space.
Solar-exposed glazing opening - a glazing opening that is environment-exposed or links to a glazing cavity (does not include glazing openings linking to other types of unheated space),
Roof - an environment-exposed non-opening element with a slope less than 70 degrees, or a link-exposed ceiling, or any link-exposed element adjacent to a room of type ‘Unheated space with pitched roof and insulation between joists/rafters’.
Rooflight - an environment-exposed glazing opening with a slope less than 70 degrees or a link-exposed ceiling window, or any link-exposed glazing element adjacent to a room of type ‘Unheated space with pitched roof and insulation between joists/rafters’.
