The average plan depth is calculated by measuring, for each room, the distance from the window nearest to the centre of the room. Then calculate the total distance for all rooms and divide this by the number of rooms. The following should also be taken into account:
- If the room is a straightforward parallelogram, the ‘centre’ of the room can be considered the midpoint between a line perpendicular to the midpoint of the external wall with the window and the opposite wall.
- If the room is more complicated, a point marked visually (by eye) is acceptable where the plans are provided as evidence.
- Alternatively, the centroid of the floor plan polygon can be calculated mathematically if the calculations are also submitted.
- Only the window nearest to the centre is considered, for each wall.
- Roof lights should not considered.
There is an element of discretion in terms of calculating this and common sense should be applied to ensure that room depth is being calculated correctly, keeping in mind that this aspect is about determining the rooms ability to circulate air as part of managing high temperatures.
Generally speaking, the average plan depth only becomes an issue for homes with relatively deep rooms and it does not tend to be a problem in the majority of cases, for the purposes of the HQM temperature tool.
The HQM temperature outputs help to determine homes that are less likely to be at risk of overheating in summer months. It is not a design tool and efforts should be applied to reduce risk wherever possible (e.g. appropriate use of ventilation and thermal modelling).