It is important to maintain the windows’ glass clean to allow a good penetration of natural light in the building and to improve their use, avoiding the use of artificial light.
It improves the internal light comfort
Reduce the use of lighting systems
Extend the life of windows
It may be difficult to clean the external glass in a building with high curtain wall, in which case a specific cleaning installation is necessary
Low investment. It includes the cost of water, detergent and manpower. The cost could be more elevated in case the installation of a specific cleaning system is required (up to 20€ for each window pane). It reduces the costs associated to the use of artificial lighting.
References and best practices
How the windows of skyscrapers get washed: citylab