How to recognise rising damp

Rising damp happens when groundwater is drawn up through the tiny pores in a wall: brick, stone and mortar. It works much like kitchen roll soaking up a spill.

It is also one of the most misdiagnosed problems in British homes. Condensation and penetrating damp can leave very similar marks, and they need completely different solutions. So before thinking about treatment, it is worth being sure.

Typical signs

• The marks start low down. They appear just above the skirting and rise, usually up to about a metre, with an uneven “tide mark” edge.
• There are salts. The water carries salts from the ground. When it evaporates, they are left behind as a white, powdery or fluffy deposit that pushes off paint and plaster.
• Ground floors and basements are affected. It is typical of walls in contact with the ground, especially in older properties without a working damp-proof course.
• It is there all year. It may get worse in wet months, but it does not go away in summer.

When it is probably something else

• Marks on ceilings, high corners or behind furniture usually point to condensation: moisture in the air turning back into water on cold surfaces.
• Patches that appear or grow after rain, especially near windows, roofs, gutters or downpipes, suggest penetrating damp.
• Black mould in cold spots that gets worse in winter with the windows shut is another sign of condensation.

How to confirm it

The reliable way is to measure. Readings are taken at different heights on the wall: if moisture is highest at the bottom and falls off higher up, the pattern fits rising damp.

Readings need interpreting with care. Salts in old plaster can make some moisture meters read high even when the wall itself is not wet, which is one reason rising damp is over-diagnosed.

At a free BiXos assessment we take these readings, record them as a baseline and explain what we have found, including if the cause turns out to be something else.