Environmental and health related criteria for buildings - ANEC

IBO - Environmental and Health related Criteria for Buildings
- All living rooms, dining rooms and studies (including any room designated as a home
office) must achieve a minimum average daylight factor of at least 1.5% (1 point).
- 80% of the working plane in each kitchen, living room, dining room and study (including
any room designated as a home office) must receive direct light from the sky (1 point).
Evidence must be provided by daylighting calculations and plans showing the angle of visible
sky, room dimensions, position and size of windows, external buildings and other
obstructions, the position of the no-sky line 62 in the room and percentage of area of the
working plane 63 that receives direct light from the sky. It is acceptable that daylighting
calculations are carried out in selected dwellings when the reasoning behind selection of
dwellings (or rooms) clearly demonstrates that the rooms in the dwellings for which the
calculations are not provided will perform better than those backed up by the calculations.
The average daylight factor is defined as the average indoor illuminance (from daylight) on
the working plane within a room, expressed as a percentage of the simultaneous outdoor
illuminance on a horizontal plane under an unobstructed CIE Standard Overcast Sky. The
Code awards credits for meeting the minimum average daylight factor suggested by BS
8206-2.
Calculations of the average daylight factor may use the following formula (method described
in Littlefair (1998) as set out in BS 8206–2) 64 or computer simulation or scale model
measurements for more complex rooms and external obstructions.
DF = M·W·T·θ / (A (1-R²))
Where:
M = a correction factor for dirt
W = total glazed area of windows or roof lights
T = glass transmission factor
A = total area of all the room surfaces (ceiling, floor, walls and windows)
R = area-weighted average reflectance of the room surfaces
θT = angle of visible sky
The average daylight factor formula can be used to model daylighting conditions in any
simple rectangular room with a continuous external obstruction or none. Where external
obstructions are of complex geometry and cannot be approximated by a continuous object, it
is advised to use methodology in Littlefair (1998). More complex room geometries can be
modelled using computer simulation software, physical scale modelling or advanced manual
calculations
For construction stage, an inspection report confirming the input data for calculations or onsite
measurements in the same rooms assessed during design stage is required.
62 The no-sky line divides those areas of the working plane which can receive direct light from the sky, from those
which cannot. It is important as it indicates how good the distribution of daylight is in a room. Areas beyond the
no-sky line will generally look gloomy.
63 The working plane is a notional surface, typically at about desk or table height, at which daylight factor or the
‘no-sky line’ is calculated or plotted. For the calculations required here, it is at 0.85m above the fl oor.
64 Littlefair, P. J., Site layout planning for daylight and sunlight, A guide to good practice”, BRE Press, 1998.
BS 8206 “Lighting for buildings - Code of practice for daylighting Part 2”, 1992.
Information Paper IP 23/93 “Measuring daylight”, BRE, 1993.
Final Report 96 31 03 2011