Indoor Air Quality

Welsh Government

Indoor humidity levels can have a significant influence on a dwelling’s air quality. High levels of relative humidity have been shown to contribute to increased levels of mould and fungus, bacteria, viruses, and mites. A relative humidity range of 40% - 60% was found to be the ideal range for favourable indoor air quality across all categories studied during the six-week period from 22nd July – 31st August. The percent of days with maximum relative humidity greater than the 60% upper bound of this range is utilised to quantify the change in risk of poor air quality. While low relative humidity can also have negative consequences, it was not assessed in this study since indoor relative humidity levels are projected to increase. The climate in Wales is also such that low relative humidity is typically not the prevailing issue.

Results are presented for the average building along with 11 building classes: three age-based classes (Pre 1919, 1919-1990, Post 1990), three wall-material-based classes (Timber frame, Solid – Stone, Solid – Brick & Cavity), three construction-style-based classes (End Terrace & Mid Terrace & Semi Detached, Detached, Flat), a class for Internal Wall Insulation (IWI) and a class for Double glazing in pre-1919 properties.

Additional information is available here: Wales Housing Climate Analysis Additional Information

Accompanying maps in this series can be found here:

Climate Projections consisting of Daily Maximum Temperature, Annual Precipitation, Daily Relative Humidity and Daily Specific Humidity

Indoor Conditions results consisting of Indoor Air Quality and Overheating

Building Fabric degradation results consisting of Solar Insolation, Precipitation and Relative Humidity 

Case Studies for four representative towns and cities illustrate results at a resolution of 2.2 km, giving insight into the variation that is projected geographically across each area:

Aberystwyth consisting of Climate, Indoor and Fabric

Cardiff consisting of Climate, Indoor and Fabric

Swansea consisting of Climate, Indoor and Fabric

Wrexham consisting of Climate, Indoor and Fabric

For a better understanding of the impact of summertime overheating on houses that have been highly insulated and suggestions on approaches to tackling them go to: Considering summertime overheating in highly insulated homes: factsheet | GOV.WALES

For a better understanding of the impact of summertime overheating on post 1985 properties (including older buildings converted into flats) and suggestions on approaches to tackling them go to: Considering summertime overheating in post 1985 properties (including older buildings converted into flats): factsheet | GOV.WALES

For a better understanding of the impact of summertime relative humidity in older properties and suggestions on approaches to tackling them go to: Considering summertime relative humidity in older properties: factsheet | GOV.WALES

For a better understanding of the maintenance, repair and adaptation priorities of older, traditional properties under a changing climate, go to: Considering repair, maintenance and adaptation priorities for older properties: factsheet | GOV.WALES

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