How to Detect and Eliminate Rising Damp


Rising damp is a relatively rare form of damp that adversely affects the walls of buildings.  This type of dampness occurs when moisture at the ground level moves up through the walls because of capillary action. In simpler words, this is comparable to ground water being sucked through the building materials through tiny tubes or a series of straws.

The water travelling up the wall contains several types of salts. Many different porous building materials as well as timber components are found around the affected walls. As a result, these materials absorb the rising groundwater, and may pose a serious structural issue if adequate measures are not taken on time.

In general, the problem of rising damp is noticed first by the damage it causes to a building’s internal walls. Some of the immediate impacts include deterioration of the paints and plaster, and loosening of the wallpaper. Often times, you may also notice a visible stain on the wall, indicating the point reached by the groundwater.  Sometimes, blooming salt particles may also be visible on the internal wall surface. As far as the external surface of the building is concerned, rising damp may result in crumbling of the mortar and appearance of white salt stains on the wall surface.

Before discussing how to eliminate rising damp, it is important to identify its signs.

Signs of Rising Damp:

The most common sign of rising damp is a tide line of brownish or yellowish staining in the wall, just above the skirting board. It is also common to have rotting or damp flooring or skirting boards. You may also observe fluffy, white deposits left in the plaster, caused by salts washed out of the bricks and into the plaster. Dark mold spots may also appear around the damp areas of your wall.

Causes of Rising Damp:

The problem of rising damp is the result of not installing a Damp Proof Course or having one that is improperly installed or aged. These waterproof layers are installed on the internal wall, near the concrete floor or under the raised timber floor. The DPCs for external walls are installed around six inches from the ground outside. These layers repel water, and many different types of DPCs are available.

Rising damp may occur even if you have a properly functioning Damp Proof Course. It has been observed that DPCs may get breached if something attached to the walls allows water to continue moving upwards by travelling around the DPC. This can happen in presence of an outside structure at a level which is above the Damp Proof Course or if there is a ground area next to the external wall at a level higher than that of the DPC. Under these circumstances, water can travel upwards through these structures and cross over the DPC.

Your Damp Proof Course may also fail to control rising damp if the internal plaster is connected directly to a solid floor at the internal wall’s bottom surface. At times, cavity walls my contain debris such as leftover building materials inside it. If this debris is allowed to go above the level of the Damp Proof Course, a bridge is created for moisture to travel as rising damp over the DPC.

Please remember that all your damp related problems may not be attributable to rising damp. In general, unevenly distributed damp patches at a level of higher than one meter on the wall are not caused by rising damp.

Rising Damp Treatment:

Before discussing ahead, please be mindful of the fact that implementing quick-fix solutions may only make the job more expensive because you may have to do it all over again in the future.

If you already know that your blocked cavity wall is causing the rising damp, unblocking the cavity may solve the problem. In case of other factors such as high outside ground, you should try to adjust or remove whatever is allowing the DPC to be bridged, so that it goes below the Damp Proof Course. If your DPC is currently buried in the ground, it is a good idea to dig a six inch deep trench. However, please ensure there is no pooling in the ditch because that will cause dampness issues of its own.

In some instances, you may find it impossible to remove the object responsible for breaching the DPC or it may be faulty.  You can still restrict rising damp by installing a new Damp Proof Course in the walls. If the structure breaching the DPC is immovable, the new DPC should be installed above the structure.

Types of Damp Proof Course:

The best option for any house owner is to install a stainless steel or plastic sheet Damp Proof Course at the time of building the house. Though it is difficult after the house is built, stainless steel sheet can still be installed into the walls using saw cut slots.

Many other simple retrofit options are also available.

Installation Guidelines to Stop Rising Damp:

Regardless of which method you opt for, if there is a cavity wall, the DPC has to be installed on both your external and internal walls. Make sure that the DPC is installed at the same level in the internal wall and six inches above the ground level outside. If the ground level outside is higher than the floor level inside, make sure that the DPC is at the same level as the concrete floor by digging up a trench in the ground.

If you still have questions related to rising damp and its treatment, please contact ExtractAir for the most up to date solutions. With over fifteen years of experience, we are amongst the most trusted sub-floor ventilation specialists in this region.