Daylighting: Natural Light in Architecture

carried out to establish the daylight effects on a number of building forms
and roof configurations.
CIBSE Guidelines recommend an average daylight factor of 5 per cent
and a minimum of 2.5 per cent within general office areas with manual
computer usage. Entrance areas and reception have a lower CIBSE
recommendation of 2 per cent average and 0.6 per cent minimum. An
improved level is anticipated due to the use of the entrance hall as a
natural light well for the rear of the offices adjacent to the entrance hall.
Three options for the street were selected from a number which were
considered, and a full daylight study was considered for each option.
Of these three, Option 1 was considered to be the most appropriate for
the following reasons:

Greater uniformity of lighting levels

Reduction of glare into offices adjacent to the street

The other two options tended to lead to ‘overlighting’ of the space

Excessive solar gain into the street, creating overheating problems

Excessive heat loss in summer.

Results from the model below the artificial sky:

Street Option 1, lower level

1. A minimum daylight factor of 3 per cent was measured with a max-
   imum of 14 per cent for the lower office area; the average being 6 per
   cent.


2. The analysis indicated an average daylight factor of 7 per cent for the
   street at floor level, ensuring that a good daylight quality would be
   achieved.

Street Option 1, upper level

A minimum daylight factor of 4 per cent was measured for the upper
office area with a maximum of 14 per cent at the perimeter, with an
average of 7.4 per cent.

Calculations 49

The model used for the analysis

Buro Happold