Where the room size is comparable and the function is the same, such as ‘kitchen’, the percentage rule needs to be applied to the total floor area. As the average daylight factor is a measure of daylight across the whole room, only whole rooms can be compliant. This is why we refer to rounding up the ‘80% of the floor area’ requirement to the rounded-up number of compliant rooms.
This rule applies to rooms of a similar size and function and compliance note ‘percentage of assessed area’ includes a simple example, where all the rooms are the same size. However, this rule can still be applied to rooms of different sizes.
Spaces whose size is substantially larger should meet the average daylight factor requirement on their own. In these cases, the percentage requirement is still applicable to the floor area of the remaining rooms.
For example, where 80% of ‘teaching, lecture and seminar spaces’ need to comply with the average daylight factor, if we have a large lecture theatre of 200m2 and 3 seminar spaces of 30m2 each, the requirements for 80% would mean 232m2 of the floor area need to comply. This would require the lecture theatre and two seminar spaces to comply.
Where a building contains different area types, the 80% minimum floor area must be calculated by each separate building area type as defined in the table listing the average daylight factors required. For example, a multi-residential building that contains kitchen areas and living room areas, would need each one of these areas to comply with the 80% minimum floor area requirement separately.
In schemes where dwellings are assessed separately, this is likely to result in 100% of the relevant dwelling areas complying. This is because in a typical house with one kitchen and one living room, an 80% requirement for the kitchen and an 80% requirement for the living room, would mean the whole kitchen and the whole living room need to comply (since only whole rooms can be compliant).
08/01/2021 Clarifications and example added.