Editing Humidity (section)

=== Building construction ===
[[File:Primary efflorescence decades later 001.png|thumb|Effects of high humidity level in a building structure ([[efflorescence|primary efflorescence]])]]
Common construction methods often produce building enclosures with a poor thermal boundary, requiring an [[Building insulation|insulation]] and air barrier system designed to retain indoor environmental conditions while resisting external environmental conditions.<ref>{{cite web|url=https://www.iea.org/reports/all-countries-targeted-for-zero-carbon-ready-codes-for-new-buildings-by-2030-2|title=Free publications|access-date=2013-12-23|archive-date=2022-10-09|archive-url=https://web.archive.org/web/20221009013832/https://www.iea.org/reports/all-countries-targeted-for-zero-carbon-ready-codes-for-new-buildings-by-2030-2|url-status=live}}</ref>  The energy-efficient, heavily sealed architecture introduced in the 20th century also sealed off the movement of moisture, and this has resulted in a secondary problem of [[condensation]] forming in and around walls, which encourages the development of mold and mildew. Additionally, buildings with foundations not properly sealed will allow water to flow through the walls due to [[capillary action]] of pores found in masonry products. Solutions for energy-efficient buildings that avoid condensation are a current topic of architecture.

For climate control in buildings using [[HVAC]] systems, the key is to maintain the relative humidity at a comfortable range—low enough to be comfortable but high enough to avoid problems associated with very dry air.

When the temperature is high and the relative humidity is low, evaporation of water is rapid; soil dries, wet clothes hung on a line or rack dry quickly, and perspiration readily evaporates from the skin. Wooden furniture can shrink, causing the paint that covers these surfaces to fracture.

When the temperature is low and the relative humidity is high, evaporation of water is slow. When relative humidity approaches 100%, condensation can occur on surfaces, leading to problems with mold, corrosion, decay, and other moisture-related deterioration. Condensation can pose a safety risk as it can promote the growth of mold and wood rot as well as possibly freezing emergency exits shut.

Certain production and technical processes and treatments in factories, laboratories, hospitals, and other facilities require specific relative humidity levels to be maintained using humidifiers, [[dehumidifier]]s and associated control systems.