BS 5250:2011+A1:2016

This British Standard gives recommendations and guidance on avoiding problems with high moisture levels and condensation in buildings. Recommendations given are based on forms of construction commonly adopted in the UK.

This British Standard gives guidance on the risks associated with excessive humidity in buildings, notably mould growth and condensation, which can endanger the health and well-being of building occupants and the integrity of the building fabric. It describes the principal sources of water vapour, its transportation and deposition and provides guidance on how to manage those risks during the design, construction and operation of buildings.

The guidance contained in this standard is relevant to buildings of all types, whatever their form, construction and occupancy. However, this standard does not cover buildings used for storage at sub-zero temperatures.

Recommendations and guidance on how to avoid penetration of the building envelope by water is contained in other British Standards, for example BS 8103‑1, BS 8103‑3 and BS 8103‑4 for floors, BS 8103‑2 and BS 8104 for walls, BS 5534 for pitched roofs and BS 6229 for flat roofs.

Essential design data are contained in the annexes to this standard, including:

• the essential relationship between temperature and moisture content of air;

• methods of calculating the risk of surface and interstitial condensation;

• typical quantities of moisture generated in buildings of various uses and levels of occupation;

• thermal conductivity and vapour resistivity values of common building materials;

• factors for the conversion of common units.