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

Operable windows

Operable windows


To increase the supply of high quality outdoor air and promote a connection to the outdoor environment by encouraging occupants to open windows when outdoor air quality is acceptable.


Achieving natural ventilation through open windows, doors and louvers can provide a positive occupant experience, but challenges the ability to maintain strict control over interior air quality. When weather and local ambient parameters indicate high quality outdoor air, WELL encourages the use of natural ventilation strategies. Open windows can then provide a supply of outdoor air and lower the levels of carbon dioxide and VOCs, such as formaldehyde, without compromising indoor air quality.

Part 1
Full Control

The following requirement is met:
Every regularly occupied space has operable windows that provide access to outdoor air and daylight.

Part 2
Outdoor Air Measurement

Outdoor levels of ozone, PM₁₀, temperature and humidity are monitored based on the following requirement, and data collected is made available to the building occupants:
A data-gathering station located within 1.6 km [1 mi] of the building.

Part 3
Window Operation Management

If the outdoor air measurement system indicates that outdoor air either (i) exceeds ozone levels of 51 ppb or PM₁₀ levels of 50 μg/m³; (ii) has a temperature of 8 °C [15 °F] above or below set indoor temperature; or (iii) has a relative humidity above 60% and the temperature is above the indoor set temperature, then one of the following is used to discourage occupants from opening windows:
Software on occupants' computers or smartphones.
Indicator lights at all operable windows.