Last edited 19 Apr 2021

Damp proofing buildings

The term ‘damp proofing’ refers to types of moisture control that are applied to walls and floors to prevent damp from setting in or spreading in a building.

Damp problems are among the most frequent problems encountered in buildings, particularly older buildings which may have been constructed without a damp-proof membrane.

Damp may be apparent from:

Damp patches.
Mould growth.
Mildew, salts, staining and 'tide marks'.
Damage to surface finishes, such as blistering paint and bulging plaster.
Corrosion and decay of the building fabric.
Slip hazards.
Frost damage.
Poor performance of insulation.
Damage to equipment, or electrical failure.

The most common causes of persistent damp in buildings are:

Condensation (surface or interstitial).
Rising damp.
Penetrating damp.

The two most common damp proofing techniques are:

Installation of a damp-proof course. A damp-proof course is a barrier, usually formed by a membrane built into the walls of a property, typically 150 mm above ground level, to prevent damp rising through the walls. Damp-proof courses are now required in the construction of new buildings to prevent rising damp and in some situations to prevent penetrating damp.

Damp proof courses can also be retrofitted to existing buildings by the injection of water-repellent chemicals. Treatment generally also involves remedial work to any corroded or decayed elements of the building fabric, as well as hacking off and replacing existing plaster to a height of 1 m.

For more information, see Damp proof course.

Installation of a damp-proof membrane (DPM). Typically, a DPM is a polyethylene sheet laid under a concrete slab to prevent the concrete from transmitting moisture through capillary action.

For more information, see Damp proof membrane.

Other damp proofing techniques include:

Integral damp proofing: Concrete production can involve the addition of materials to make it more impermeable.
Surface coating: Waterproof surface materials can be used internally or externally, such as render or waterproof plaster.
Cavity wall systems: A cavity separates the interior walls from the exterior walls.
Pressure grouting: This can fill in cracks and joints in masonry.
Colourless water-repellent treatments.

However, it is important to note that damp is often just a symptom of another problem in a building, such as a lack of ventilation, drainage problems, cracks in walls, missing tiles or leaking pipework. It is important therefore that the underlying problem is rectified before other treatments are applied.