Rising Damp – a short guide

Walls need to breathe.

Dampness is one of the most common issues found in old buildings.

However, the problem is not caused by the way the buildings were originally constructed. The truth is – dampness is caused by the changes we make to the property over time.

When these buildings were originally built, they were designed so the sub-floor space would ventilate. This meant the lower portion of the walls could dry before reaching the Damp-Proof-Course (DPC) – as shown below. The process of allowing water to go in and out of the walls is commonly refereed as letting the walls breathe.

What causes rising damp?

Rising damp occurs in buildings where water from the ground has no other way of escaping other than rising through the walls of your building. The larger the amount of water the higher it will rise.

Any changes made to the base of the wall or around it, can cause water to bypass the DPC. The result is dampness rising in the wall, which can show inside and outside.

Raising the ground level.

One of the most common changes which causes dampness is the raising of the ground level outside the building.  While it might seem harmless, this can allow high levels of moisture into the wall.

Once the soil covers the DPC, it allows water to completely bypass it and travel freely up the wall.

Soil can also cover sub-floor vents, allowing trapped moisture to be absorbed not only by your walls, but also by your timber floors. In some cases, the moisture level gets so high that your timber floors rot.

Changing the interior flooring system.

Another common change which causes rising damp is the addition of concrete to the interior floors. This is particularly common in kitchens and bathrooms for tiling over it but could sometimes be added to the interiors of the entire building.

The rising damp is caused due to infill being added to the sub-floor space, with the concrete slab poured over. This means there is no longer any sub-floor ventilation, with the infill directly absorbing the ground moisture.

That moisture is then absorbed by the walls, both below and above the DPC, travelling up until it evaporates.

How to address rising damp?

The first step to address rising damp is to check for the source of the water.

It could be one of the changes noted above, or something as simple as an unconnected downpipe or a leaking water tap.

The key is to reduce the moisture around the walls and keep all water below the DPC and the sub-floor vents so they may work as planned.

Once the source of the water is removed, you will need to allow the wall to dry out for a few months.

If painted walls are peeling, it is best to remove the paint using a paint removal system to make the drying process easier.

Once the wall is dry, re-do your wall finishes as required. This may include re-pointing your brick wall or repainting.

If you choose to re-point, remember to use a lime render. If you choose to re-paint, avoid using plastic paints and use a breathable paint instead.

Having trouble finding the source?

If you have looked all around and still can’t find the source of the water, don’t worry. Just because the source is not easily found, it doesn’t mean it is not easily fixed.

Avoid the “miracle” modern solutions, such as seal coatings/paints and injectable chemicals. They often make the issue worse by trapping even more water in yours walls.

As heritage professionals, we can easily spot the issue and suggest the best way to address it – saving you time, money and a lot of effort.

If you need a hand please reach out to us at Arcade Heritage Architects, and we will get your walls dry in no time.