A habitable attic generally meets the following criteria:
In cases where an attic meets most of these criteria and is clearly and effectively employed as a habitable area by the occupants then it may be considered as habitable for the purposes of DEAP assessments, even if it may not be in line with good room design guidance for the ventilation of habitable rooms provided in TGD F. For example, a 1.95m high attic with bedrooms, finished surfaces, lighting, windows, no water cistern and no obstructive structural timbers is considered habitable. To be considered habitable, attics must be accessed by a fixed staircase. When habitable, according to these criteria, attics are included as a separate storey under ’dimensions‘ in DEAP.
Where an attic is not considered habitable, based on the criteria above, then the attic’s floor area is not included as part of the dwelling floor area. In this case, the following applies in relation to the storey height and the inclusion of the attic volume:
When porches or garages are not included in in the assessment floor area, the door and part of the wall between the dwelling and these structures are adjacent to an unheated space and their U-values should be calculated accordingly (see Section 2).
In buildings incorporating flats, where corridors and stairwells are heated, walls between the flat and heated corridors/stairwells should be treated as non-heat loss walls (that is assuming the same temperature on either side of the walls). Otherwise, these walls are treated as elements adjacent to an unheated space and their U-values should be calculated accordingly (see Section 2).
No special treatment is required where a central heating boiler is located in an unheated garage (that is the floor area should be the same as if the boiler were in the kitchen or a utility room).