Daylighting – Floor areas for average daylight calculations

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.

Where a building contains different area types, the 80% minimum floor area must be calculated by each separate area type. For example, a multi-residential building that contained kitchen areas and living room areas would need both of these areas to comply with the 80% minimum floor area requirement separately.