It is well documented that humidity plays an important role in assuring the wellbeing of building occupants. In the UK, more than 80% of our time is spent indoors, and with approximately 90% of the associated costs of a building being staff related (1), providing good indoor environmental quality is essential.
The recommended levels of humidity vary depending on the situation (for example, offices, data centres, hospitals and so on). In some industrial applications (such as heritage or storage), moisture stability is essential for preservation. In offices, the generally accepted levels of humidity may range between 40 and 60% (2).
As a standalone parameter, humidity is unlikely to cause thermal discomfort and levels outside the 40-60% range can easily be tolerated. A 10% increase in relative humidity is felt to be as warm as a 0.3°C rise in the operative temperature (3).
Human perception of dry air is generally due to contaminated or too warm air rather than physical dryness (4) and air with high humidity is often perceived as odorous (5).
“Humidity extremes are undesirable and affect human comfort, productivity and health. Long periods of exposure to humidity levels under 35% should be avoided as they can cause eye irritation, throat and nose dryness (6). This is a common occurrence in aircraft, where humidity levels can be as low as 20 per cent (7).
"Low humidity levels can also increase static electricity, which is a bigger cause of concern in data centres, where equipment can be damaged (8) or in places where there might be risk of gases igniting (1).
"At the other end of the spectrum, high levels of humidity encourage bacteriological and mould growth (2, 6) and increase the chemical and sensory emission from water borne building varnish and paint (9), contributing to poor indoor air quality.
"In summary, controlling the humidity levels and regular maintenance of the systems in an office building will avoid future costly problems related to mould growth and also contribute to the wellbeing and productivity of the occupants.”
This article was originally published here in August 2017 by BSRIA.
 Related articles on Designing Buildings Wiki
- BSRIA articles on Designing Buildings Wiki.
- Comfort in low energy buildings.
- Dry-bulb temperature.
- Evolving opportunities for providing thermal comfort.
- Heat stress.
- Indoor air velocity.
- Mean radiant temperature.
- Thermal comfort.
- Thermal pleasure in the built environment.
- Wellbeing and creativity in workplace design - case studies.
- Workplace air conditioning.
 External resources
- Wellbeing and productivity in Offices report. World Green Building Council’s Health, 2014.
- Guide A Environmental design. Chartered Institution of Building Services Engineers, 2015.
- BS EN ISO 7730: 2005 Ergonomics of the thermal environment. Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria. BSI, 2006.
- Sundell, J, On the association between building ventilation characteristics some indoor environmental exposures, some allergic manifestations and subjective symptom reports. Indoor Air. Supplement no2/94 pp 5-49,1994.
- Fang L, Clausen G and Fanger P O, Impact of temperature and humidity on the perception of indoor air. Indoor Air vol 8, no 2, pp 80-90, 1998.
- Potter, I N, The sick building syndrome. BSRIA Technical Note 4/88, 1988.
- World Health Organisation http://www.who.int/ith/mode_of_travel/chad/en/
- Thermal Guidelines for Data Processing Environments. ASHRAE, 2015.
- Fang L, Clausen G and Fanger P O, Impact of temperature and humidity on chemical and sensory emissions from building materials. Indoor Air, vol 9, no 3, 193-201, 1999.
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