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How to Treat Damp in Walls

Damp in walls can be a homeowner’s nightmare, leading to structural damage, unsightly damp patches, and potential health risks. Understanding the causes and how to treat damp in walls effectively can help you maintain a healthy and safe environment at home. Here’s a step-by-step guide on identifying, treating, and preventing damp in your walls.

Step 1: Identify the Type of Damp

Damp in your walls can manifest in various forms with distinct causes and characteristics. Accurately identifying the type of damp affecting your home is critical as it determines the most effective treatment method.


Condensation is the most common form of damp in homes and is typically easier to address. It occurs when moist air condenses into water on colder surfaces, such as walls and windows.

  • Water droplets on windows and walls
  • Peeling wallpaper
  • Black mould growth, particularly around windows, on ceilings, and in corners of rooms
  • Lack of ventilation: Common in kitchens and bathrooms where steam is generated
  • Inadequate heating: Cold surfaces in the home can exacerbate condensation
  • Excess moisture generation: Everyday activities like cooking, drying clothes indoors, and showering without proper ventilation

Rising Damp

Rising damp results from ground water moving up through a building’s fabric by capillary action. It usually occurs in older buildings that either lack a damp-proof course (DPC) or have a damaged one.

  • A ‘tide line’ of yellow or brown staining or discolouration just above the skirting boards
  • Damp patches that start at the floor and can rise the wall up to one metre
  • Peeling paint and wallpaper, often with a characteristic ‘wavy’ edge at the top of the damp area
  • Salts within the plaster leaving a white, fluffy deposit
  • Absence or failure of a damp-proof course (DPC)
  • Bridging of the DPC due to raised external ground or internal floor levels

Penetrating Damp

Penetrating damp occurs when water enters a building from the outside to the inside, often driven by wind, through faults in the building envelope or due to exposure to prolonged or heavy rainfall.

  • Damp patches on walls or ceilings that may darken after rain
  • Localised dampness correlating to external defects
  • Growth of moss or lichens on external walls
  • Structural problems such as faulty roofing, cracked or missing tiles, or defective pointing
  • Overflowing gutters and downpipes leading to water spillage on the walls
  • Window frames or doors that are not adequately sealed

Step 2: Diagnosing the Problem

Once you’ve identified the type of damp affecting your walls, the next crucial step is accurately diagnosing the specific causes. This involves a detailed inspection both inside and outside your home to identify any potential issues contributing to damp. Here’s how you can go about diagnosing the problem based on the type of damp you’ve identified.

Diagnosing condensation

Condensation-related damp is primarily caused by poor ventilation and excess indoor moisture. To diagnose issues leading to condensation, check areas with high humidity, such as kitchens, bathrooms, and utility rooms. Look for signs like streaming windows and walls, mould growth, and musty smells. Ventilation should be assessed; check if extractor fans are present and working, if air vents are blocked, and if windows are regularly opened to allow air exchange. Additionally, lifestyle factors that increase moisture should be considered, like drying clothes indoors without adequate airing and frequent use of humidifiers.

Diagnosing rising damp

To diagnose rising damp, inspect the lower sections of your walls for dampness or tide marks above the skirting boards. Check the external ground level; it should be at least 150mm below the damp-proof course (DPC) to prevent bridging. If the external ground level is not an issue, the problem might be a faulty or absent DPC. Older properties may have been built without a DPC, or it may have degraded over time. A professional assessment might involve checking the DPC with specialized equipment to detect moisture levels and integrity.

Diagnosing penetrating damp

For penetrating damp, you need to thoroughly inspect the exterior of your property. Look for any signs of damage, such as cracked bricks, defective pointing, and damaged roofing, that may allow water ingress. Ensure gutters and downspouts are clear of debris and functioning correctly, as blocked gutters can cause water to overflow and penetrate the walls. Pay special attention to any damp patches that correlate with rain; this is a strong indicator of where water might be entering. Additionally, check around windows and door frames for any gaps or failing sealant that might allow water to seep through.

Step 3: Treating the Damp in walls


  • Improve Ventilation: Install vents or extractor fans, especially in high-moisture areas like kitchens and bathrooms.
  • Use a Dehumidifier: Reducing the moisture level in the air helps prevent condensation.
  • Heat Your Home Evenly: Keeping a consistent temperature can reduce the likelihood of condensation.

Rising damp

  • Damp-Proof Course (DPC): Installing or repairing a DPC can stop water from rising through the walls.
  • Reroute Water: Ensure that all groundwater is directed away from the building’s foundations.

Penetrating Damp

  • Repair External Faults: Fix any damaged roofs, pipes, or guttering. Repointing bricks can also prevent water from entering.
  • Waterproof External Walls: Applying a waterproof coating or render can provide an extra barrier against water.

Step 4: Preventing Future Damp in walls

Once you’ve treated the existing damp issues in your home, the next crucial step is implementing measures to prevent recurrence. Maintaining a damp-free home requires good building maintenance, adequate ventilation, and moisture management.

Regular maintenance checks

Regularly inspecting your home for early signs of damp and potential vulnerabilities can prevent minor issues from developing into major problems. Check your roof for missing or broken tiles and ensure all flashing is intact and functional. Gutters and downspouts should be cleaned at least twice a year to remove leaves and debris that could cause blockages and lead to water overflow against walls. Examine the exterior walls for cracks or missing mortar in the brickwork, and look for any signs of soil build-up that might bridge the damp-proof course.

Improving ventilation

Adequate ventilation is critical in preventing condensation-related damp. Ensure that all rooms, especially kitchens and bathrooms, are well-ventilated. Installing extractor fans in these areas can help reduce moisture levels. Consider the benefits of trickle vents in windows or humidity-controlled ventilation systems in other parts of the home. During colder months, maintain a low level of constant heating to avoid cold surfaces where condensation can form, and make sure furniture is slightly away from walls to allow air to circulate freely.

Effective landscaping

The way your garden is landscaped can impact your home’s dampness. Ensure that the ground slopes away from your home so that rainwater drains naturally away from the foundation. Consider installing drainage solutions like French drains if you experience standing water near your home after heavy rains. Keep plants and shrubbery trimmed back from the walls to prevent dampness from being trapped and to allow sunlight to keep the walls dry.

Smart heating and humidity control

Investing in a smart heating system can help you control the indoor climate more effectively, reducing the risk of condensation. Smart thermostats can maintain a consistent temperature that discourages condensation without overheating your home, which can be cost-effective and beneficial for damp prevention. Humidistats can be installed to control devices like dehumidifiers automatically, turning them on when humidity levels rise above a set point.

Ongoing monitoring

Even after implementing preventative measures, keep a close eye on the effectiveness of these strategies. Regularly check known problem areas for signs of moisture. If you live in an area prone to damp issues, consider an annual inspection by a professional to ensure that all damp-proofing measures are intact and functioning as expected.

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