This section explains the problems you can have with damp and excessive humidity, and how to remedy them.

Note also the comments in relation to building surveys and damp.

Note that condensation in the winter on single-glazed windows is normal and does not indicate excessive damp. Damp and humidity is not a 'problem' unless it is excessive and persists all year.

With older, brick-built houses, the walls are often porous; they can get damp. The rules for damp in the walls are:

  • minimise water reaching the walls (outside - good guttering etc, gravel at the footings to avoid splashing, inside - keep good ventilation)
  • maximise evaporation (outside - avoid wall paints and treatments, inside - avoid vinyl paints and papers)

For condensation the rules are:

  • ventilate - opening a window or adding a vent will reduce the amount of water vapour
  • insulate - reducing cooling will prevent water vapour from condensing
  • heat - increasing the temperature of a window, wall or room will prevent water vapour from condensing
  • use moisture-absorbing trays on window sills

Do not over-ventilate otherwise you will reduce the temperature and the remaining moisture will condense; the art is in achieving a balance.