What is Rising Damp?

Rising damp is a form of structural dampness that becomes evident when moisture rises up through walls, floors and masonry. This moisture travels through the porous structure of a building using capillary action. Defined as the movement of water within the spaces of a porous material, capillary action occurs through forces of adhesion, cohesion, and surface tension.

The moisture will reach a certain height, at which point gravity will allow it to travel no further. This is typically around 1.2m, but salt deposits and other such by-products of damp may be present higher than this. Rising damp often occurs as a result of a damp-proof course that has become ineffective due to age or poor installation. It can also occur in buildings that have been constructed with no prior DPC.

Rising damp can normally be identified visually with a horizontal ‘tide mark’ of damp appearing above skirting boards. In concurrence with this, peeling wallpaper and salt deposits are often present in areas that experience rising damp.

Problems Associated with Rising Damp

• The moisture content of the structure can reach a point at which bacteria and organisms may grow, possibly leading to an unhealthy environment.
• In very damp conditions, external mortar may crumble, as well as steel and iron elements of the building potentially corroding and failing: both of which may pose a significant structural issue.
• Damp conditions within a wall caused by rising damp, particularly in conjunction with internal moisture, allow the growth of moulds both on the surface and within porous or fibrous materials. As well as this being aesthetically undesirable, it can also pose a health hazard.
• Exposure to microbial contaminants caused by rising damp is clinically associated with respiratory issues, allergies, asthma and immunological reactions.

Heritage and Historic Buildings

Many older or historic buildings are often constructed without the addition of a damp-proof course. Due to the breathability and natural equilibrium of the materials involved, moisture is able to evaporate with ease, which minimalizes potential damp. Despite this, modern interventions as a means of either renovating or developing these buildings, can compromise the existing materials thus allowing dampness to develop. Using modern materials that are often impermeable, without careful consideration of drainage slopes can trap moisture within, developing issues concerning rising damp.