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

Daylighting fenestration

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 façades along regularly occupied spaces:

a. 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.
b. Between 40% and 60% of window area is at least 2.1 m [7 ft] above the floor (Daylight Glass).
Part 2: Window Transmittance in Working and Learning Areas

The following visible transmittance (VT) conditions are met for all non-decorative glazing:

a. All glazing located higher than 2.1 m [7 ft] from the floor (Daylight Glass) has VT of 60% or more.
b. All glazing located 2.1 m [7 ft] or lower from the floor (Vision Glass) has VT of 50% or more.
Part 3: Uniform Color Transmittance

All windows used for daylighting meet the following requirement:

a. 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:

a. Between 30% and 60% in living rooms.
b. Between 20% and 40% in bedrooms.
Muscular
Nervous
Reproductive
Cardiovascular
Digestive
Endocrine
Immune

Applicability Matrix

Core & Shell New & Existing Buildings New & Existing Interiors
Part 1: Window Sizes for Working and Learning Spaces O O O
Part 2: Window Transmittance in Working and Learning Areas O O O
Part 3: Uniform Color Transmittance O O O
Commercial Kitchen Education Multifamily Residential Restaurant Retail
Part 1: Window Sizes for Working and Learning Spaces O O - - O
Part 2: Window Transmittance in Working and Learning Areas O O - - O
Part 3: Uniform Color Transmittance O O O - O
Part 4: Window Sizes for Living Spaces - - O - -

Verification Methods Matrix

Letters of Assurance Annotated Documents On-Site Checks
PART 1 (Design)
Window Sizes for Working and Learning Spaces
Architectural Drawing Spot Check
PART 2 (Design)
Window Transmittance in Working and Learning Areas
Architect
PART 3 (Design)
Uniform Color Transmittance
Architect
PART 4 (Design)
Window Sizes for Living Spaces
Architectural Drawing Spot Check