Building Surveying
Apr 30, 2024

Wall Damp Guidance

The ability to breathe is a must for every building structure. In our damp UK climate, water vapour tends to settle...


The ability to breathe is a must for every building structure. In our damp UK climate, water vapour tends to settle on surfaces where air or sun is not plentiful. Examples include the inside of cavity walls, roof tile membranes, etc.).


The inclusion of breathing vents for cavity walls, for instance, will allow air to absorb and dispose of any damp, provided there is actual circulation. 

Cavity Fill Insulation

In a bid to improve the thermal performance of buildings, cavity fill insulation was introduced. This would increase the energy performance (EPC) rating, but could actually cause longer-term ventilation issues, as the air between cavity walls needs to circulate in order to limit the build up of mould growth and damp. It is for the above reasons that cavity wall insulation is not necessarily recommended.

Damp & Mould

In the era during which a retrofit property was constructed, the accumulation of damp through condensation or rising damp from the soil can cause respiratory ailments because of the fungus and mould that comes with it. However, this was not fully understood at the time of build. Thereafter, damp proof course membranes (DPCs) came into existence.


Contrary to popular belief, bricks are not waterproof. They absorb water.  A DPC, which is nothing more than a strip of high quality rubber compound laid ontop of the 2nd or 3rd course of brickwork (150 mm) before the rest of the bricks are laid on top,  is what aims to prevent rising damp. 

Rising Damp

Rising damp is moisture from soil and permeable foundations being sucked up vertically by capillary action.

If the property you intend on purchasing has medium levels of damp readings, this may be acceptable, particularly if there is no flaking paint, mould growth, smell or similar unpleasant effects that are usually associated with rising damp.

Damp Proofing

If the walls are already built, one can not insert a DPC. However, you may opt for high pressure injection of a silicone liquid at the place where a modern DPC would ordinarily be. This can block water from travelling upwards. This is a typical recommended remedy, particularly as it very cost effective. 


If your surveyor has detected damp readings, but there are no significant symptoms which affect your health or the structural integrity of the building, then you may wish to wait and see if the damp dries up before carrying out inconvenient repairs.

Bear in mind that the longer you wait the more any repairs would costs (e.g. hacking off blown render, dust protection of furniture, redecorating, and potential rot of any timber floor joists or metal pipes embedded in or under the wall). Sometimes the damage is not always visible to the eye.

Solid v Cavity

Unlike cavity walls, which have an insulating effect due to the gap of air between brickwork, any water in solid walls is more susceptible to freezing. Water freezing means expanding ice. Expanding ice could lead to cracks, which in turn could lead to more water ingress. This is a vicious cycle. In other words, solid walls will/could suffer more from rising damp in a below zero climate than cavity walls.


So, a damp course injection should stop any more rising damp accumulating in walls with existing dampness, whilst allowing the moisture that is already present to evaporate (this can take a few months). Your walls should therefore “breathe” by maintaining an equilibrium between natural moisture inside bricks and ambient air.