What Is Rising Damp? A Comprehensive Guide

Rising damp is a common problem that affects buildings, particularly older properties. It occurs when moisture from the ground travels upwards through the walls of a building by capillary action. This can lead to a range of structural and aesthetic issues, and if left untreated, rising damp can cause long-term damage to a property. In this article, we’ll answer the question “what is rising damp,” delve into the causes, signs, and effects of rising damp, and explore the solutions for dealing with this issue.

What Is Rising Damp?

It’s a phenomenon where water from the ground seeps into a building’s walls and rises through the brick or stonework. This occurs because porous materials like bricks and mortar have tiny capillaries that allow moisture to travel upward against gravity. While a damp-proof course (DPC) is often installed to prevent this from happening, older buildings may lack an effective DPC or have a compromised one.

To understand what is rising damp, it’s essential to recognise that it is different from other types of damp, such as condensation or penetrating damp. Rising damp specifically refers to moisture travelling vertically from the ground, which can lead to damage at the lower levels of a building.

Causes of Rising Damp

Understanding what causes dampness is crucial for preventing and treating it. Several factors contribute to the development of dampness, including:

1. Absence or Damage to the Damp-Proof Course: One of the primary reasons rising damp occurs is the absence or deterioration of a damp-proof course. In many older buildings, especially those built before the 20th century, DPCs may either be missing or have degraded over time, making the building susceptible to damp.
2. Porous Building Materials: Some buildings are constructed with materials that are more porous than others, such as sandstone or older bricks. These materials have more capillaries through which water can travel, making them more prone to rising damp.
3. High Water Table: In areas where the water table is high, the soil around the building can remain saturated with water for extended periods. This increases the likelihood of water being drawn up through the walls, leading to rising damp.
4. Changes in Ground Levels: Modifications around a building, such as adding paving or raising external ground levels, can lead to rising damp. When the external ground level is raised higher than the damp-proof course, moisture can bypass the DPC and start seeping into the walls.
5. Blocked Drains or Poor Drainage: Poor drainage or blocked drains around the foundation of a building can cause water to pool near the base of the walls, increasing the risk of dampness.

Signs and Symptoms

Now that we’ve covered what is is and its causes, let’s discuss how to identify it. Recognising the signs early can prevent further damage to the property. Some common signs of damp include:

1. Tide Marks on Walls: One of the most visible signs of rising damp is a “tide mark” on the lower portion of interior walls. This mark is usually between 1 and 1.5 meters high and indicates where the moisture has risen before evaporating.
2. Peeling Paint or Wallpaper: As moisture rises through the walls, it can cause paint or wallpaper to peel away. This is a common symptom in older properties where the damp-proof course may be failing.
3. Damp or Musty Smell: A damp smell in the home can be a sign of moisture in the walls. The musty odor is caused by the presence of moisture and can be one of the first indications of rising damp.
4. Salt Deposits: Rising damp often brings salts from the ground with it. As the water evaporates from the walls, it leaves behind white, powdery salt deposits known as efflorescence. These deposits can cause further damage to plaster and brickwork.
5. Stained or Damaged Plaster: Plaster that is crumbling or discoloured, particularly at the lower levels of walls, is another common indicator of damp. The moisture causes plaster to weaken, leading to cracks or a “blown” appearance.
6. Wet or Rotted Skirting Boards: Wood near the base of the walls, such as skirting boards, can absorb moisture from damp. This can cause them to swell, warp, or rot over time.

Effects of Rising Damp on Buildings

The effects of rising damp can be serious if not addressed promptly. Beyond the immediate cosmetic issues, dampness can compromise the structural integrity of a building. Here’s a look at some of the potential long-term consequences:

1. Structural Damage: Over time damp can weaken brickwork and mortar. The water and salts drawn into the walls can erode these materials, compromising the strength of the structure.
2. Damage to Plaster and Paintwork: Plaster can deteriorate rapidly in the presence of rising damp. If the problem persists, walls may require extensive replastering and repainting.
3. Rotting Timber: Damp can also lead to timber decay, especially in skirting boards and floorboards. Damp conditions can encourage wet rot or dry rot to develop, leading to further complications and the need for costly repairs.
4. Health Hazards: Damp conditions can also promote the growth of mold and mildew, which can pose health risks to occupants, particularly those with respiratory conditions such as asthma.
5. Reduced Property Value: Properties with visible signs of damp are less attractive to potential buyers. Even if the damp is addressed, the property’s value may still be affected due to the perception of prior damage.

How to Treat The Issue

If you suspect rising damp in your property, it’s important to take action as soon as possible to minimise damage. There are several methods for treating rising damp, depending on the severity of the issue.

1. Damp-Proof Course Injection: One of the most common methods of treating rising damp is by injecting a chemical damp-proof course into the walls. This creates a barrier that prevents moisture from rising through the wall.
2. Membrane Systems: A damp-proof membrane can be applied to the walls to block moisture from rising. This is often used in conjunction with other treatments, such as chemical injection, to ensure a comprehensive solution.
3. Improving Drainage: In some cases, the problem may be exacerbated by poor drainage around the building. Ensuring that gutters and drains are functioning properly and that the ground slopes away from the building can help reduce the risk of damp.
4. Replastering: After treating the underlying cause of damp, it is often necessary to replaster affected walls. Specialised plaster that resists moisture is typically used to prevent future issues.
5. Ventilation: Ensuring good ventilation in the home can help to reduce humidity levels and prevent damp from developing. While this won’t stop rising damp, it can help to mitigate some of the side effects, such as mold and mildew growth.

How to Prevent Rising Damp

Understanding what is rising damp can help in taking steps to prevent it from occurring in the first place. Here are some proactive measures that can be taken to reduce the risk of rising damp:

1. Install or Maintain a Damp-Proof Course: Ensuring that your property has an effective damp-proof course is the most important step in preventing rising dampness. If your home does not have one, or if the current DPC is compromised, consider having one installed or repaired.
2. Regularly Check External Ground Levels: Make sure that the ground level outside your home does not rise above the damp-proof course. If necessary, lower the ground level or install drainage to keep water away from the walls.
3. Inspect Gutters and Drains: Keep your gutters, downpipes, and drains clear of debris to prevent water from pooling near the base of your walls. Regular maintenance can help prevent excess moisture from entering your home.
4. Choose Non-Porous Building Materials: If you’re involved in construction or renovation, opt for building materials that are less porous and resistant to moisture. This can help to minimise the risk of rising damp.

Conclusion

It’s clear that this is a serious issue that can cause long-term damage to a building if not treated properly. Rising dampness is caused by moisture travelling upward from the ground through the walls of a property, and it can lead to visible signs such as tide marks, peeling paint, and salt deposits.

Addressing rising dampness involves identifying and treating the underlying cause, which could be a compromised damp-proof course, poor drainage, or other factors. By taking preventative measures, such as maintaining a functional DPC and ensuring proper drainage, you can protect your property from the damaging effects of rising damp.

Understanding this will allow you to take action quickly, ensuring your property remains safe and structurally sound for years to come.