Moisture in buildings

Moisture is the presence of water, often in small or even trace amounts. Moisture can be found in water vapour, condensation, and in or on the fabric of a building and can cause damp resulting in problems such as staining, mould growth, mildew and poor indoor air quality, and so on.

The common sources of moisture in buildings include:

• Condensation.
• Penetrating damp.
• Leakage from pipes, tanks, drains, and so on.
• Rising damp.
• Building defect, e.g. lack of adequate roof space ventilation, faulty retrofit installation, application of paint or plaster that affects the breathability of the building element, and so on.
• Indoor moisture sources, e.g. cooking, bathing, washing, hot tubs, indoor swimming pools, and so on..

Moisture levels can be reduced through a number of measures:

• Natural or mechanical ventilation.
• Use of de-humidifiers or air conditioning units.
• Insulation of cold surfaces, such as pipes.
• Increasing air temperature.
• Removing sources of moisture such as drying clothes and ensuring vented tumble dryers are appropriately vented to the outside.
• Mending leaking pipes, wastes and overflows.
• Eliminating rising damp and penetrating damp.
• Introducing moisture barriers such as vapour barriers, damp proof membranes, and so on.

NB Technical paper 35: Moisture measurement in the historic environment, published by Historic Environment Scotland in 2021, defines moisture as: ‘Water that is freely mobile as a liquid, gas (vapour), and solid (ice). All moisture is water, but not all water is moisture, as it is not necessarily freely mobile.’

It defines moisture content as: ‘The quantity of moisture present within a material.’

[edit] Related articles on Designing Buildings Wiki

• Cavity wall insulation.
• Condensation.
• Damp.
• Damp proofing.
• Dew point.
• Electrical resistance meters.
• Humidity.
• Insulation.
• Mould growth.
• Penetrating damp.
• Rising damp.
• Types of water.
• Ventilation.
• Wall insulation and moisture risk.
• Water.
• Water vapour.