This is a legacy version of the WELL Building Standard. Please check the latest version here.

Daylighting fenestration

Daylighting fenestration


To optimize occupant exposure to daylight and limit glare through enhanced fenestration parameters.


Exposure to natural light can improve occupant mood, alertness and overall health. Ideal lighting involves proper exposure to diffuse daylight, as well as careful design of windows and glazing to avoid excessive glare and heat gain. Windows are therefore a key variable for both ensuring that occupants receive enough light for positive physiological and subjective effects, but also not too much light that causes discomfort or becomes a source of distraction. Balancing energy performance, thermal comfort and access to quality daylight are essential to proper building design.

Part 1
Window Sizes for Working and Learning Spaces

The following conditions are met on fa├žades along regularly occupied spaces:
Window-wall ratio as measured on external elevations is between 20% and 60%. Percentages greater than 40% require external shading or adjustable opacity glazing to control unwanted heat gain and glare.
Between 40% and 60% of window area is at least 2.1 m [7 ft] above the floor.

Part 2
Window Transmittance in Working and Learning Areas

The following visible transmittance (VT) conditions are met for all non-decorative glazing:
All glazing (excluding skylights) located higher than 2.1 m [7 ft] from the floor has VT of 60% or more.
All glazing located 2.1 m [7 ft] or lower from the floor has VT of 50% or more.

Part 3
Uniform Color Transmittance

All windows used for daylighting meet the following requirement:
The visible light transmittance of wavelengths between 400 and 650 nm does not vary by more than a factor of 2.

Part 4
Window Sizes for Living Spaces

Window/wall ratio as measured on external elevations is:
Between 30% and 60% in living rooms.
Between 20% and 40% in bedrooms.