Structural Dampness: How to Identify, Prevent, and Treat It

by Joost Nusselder | Updated on:  June 23, 2022
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Structural dampness is the presence of unwanted moisture in the structure of a building, either the result of intrusion from outside or condensation from within the structure. A high proportion of damp problems in buildings are caused by condensation, rain penetration or rising damp.

It’s important to know the signs and symptoms of structural dampness so you can take the necessary precautions to protect your health. In this article, I’ll explain what it is, how to identify it, and how to treat it.

What is structural dampness

How to Spot Structural Dampness: Signs and Symptoms

Structural dampness can cause a range of visible symptoms, including:

  • Stains on walls, ceilings, and floors
  • Peeling or blistering paint or wallpaper
  • Deteriorating plaster
  • Loose or crumbling mortar between bricks or stones
  • White, powdery salt deposits on surfaces

Effects on Buildings

The effects of structural dampness can be severe and long-lasting. Some of the most common issues include:

  • Rot and decay of wooden structures, including floors, joists, and roof timbers
  • Corrosion of steel fasteners and other metal elements
  • Infestation by moulds and fungi, which can cause health problems and eventually lead to replastering or even rebuilding
  • Damage to the building’s structural integrity, which can result in collapse or other safety hazards

Prevention and Treatment

Fortunately, there are several ways to prevent and treat structural dampness, including:

  • Proper waterproofing and damp proofing during construction
  • Regular maintenance and inspections to identify and address potential issues
  • Installation of ventilation systems to reduce humidity levels
  • Use of mould-resistant materials and coatings

The Culprits Behind Dampness in Buildings

Condensation is the most common cause of dampness in buildings, especially during the colder months. It occurs when warm, moist air comes into contact with a cold surface, causing the water vapor to condense into liquid form. This excess moisture can lead to a range of problems, including mold growth, peeling wallpaper, and damp patches on walls. To prevent condensation, it’s important to keep the internal moisture level of the building low by ensuring proper ventilation and heating.

Rain Penetration: The External Culprit

Rain penetration is another common cause of dampness in buildings. It occurs when water from outside the building finds its way into the structure, often through gaps or cracks in the walls or roof. This can cause damage to the building’s structure and create damp patches on walls. To prevent rain penetration, it’s important to regularly inspect the building’s exterior and carry out any necessary repairs.

Rising Damp: The Ground Up Culprit

Rising damp is caused by water traveling up from the ground and into the walls of a building. This can occur when the building’s damp proof course (DPC) is damaged or absent, allowing water to carry on rising up the walls. Rising damp can create a range of issues, including mold growth, damage to the building’s structure, and damp patches on walls. To prevent rising damp, it’s important to ensure that the building has a functioning DPC and to carry out any necessary repairs.

High Humidity: The Airborne Culprit

High humidity levels can also create dampness in buildings, especially in areas with poor ventilation. This excess moisture can lead to mold growth, peeling wallpaper, and damp patches on walls. To prevent high humidity levels from causing dampness, it’s important to ensure proper ventilation and to use dehumidifiers if necessary.

Structural Dampness and Its Troublesome Health Effects

Structural dampness is the unwanted presence of excess moisture in buildings, usually caused by water penetration, condensation, or rising damp. It can result in significant damage to the structure and materials of a building, as well as potential health risks for humans and pets.

Health Concerns Associated with Structural Dampness

The presence of dampness in a building enables the growth of mould, bacteria, and fungi, which can lead to a range of health problems, including:

  • Respiratory issues: Dampness can cause airborne concentrations of mould spores, which when inhaled, can trigger asthma and other respiratory illnesses.
  • Allergenic or immunological illness: Exposure to mould and other damp-related allergens can cause allergic reactions and immunological illnesses.
  • Nonallergic illness: Dampness can also cause nonallergic illnesses, such as headaches, fatigue, and irritations of the eyes, nose, and throat.

How Structural Dampness Triggers Asthma

The sensitization of dust mites that accrue in humid, wet regions of a structure can trigger asthma. Dust mites are a common allergen that tend to thrive in damp environments. When inhaled, they can cause asthma symptoms to worsen.

The Risk of Secondary Health Issues

Structural dampness tends to cause secondary health issues that can be just as troublesome as the primary ones. These include:

  • Infestation of pests: Damp environments attract pests such as rodents, insects, and mites that can cause further health risks.
  • Rot and deterioration of materials: Dampness can cause plaster, paint, wallpaper, and other materials to deteriorate, leading to loose surfaces, stains, and salts that mar the quality of the building.
  • Poor indoor air quality: Dampness can cause the air quality inside a building to become poor, leading to a range of health issues.

Spotting Structural Dampness: A Guide to Identifying the Culprit

Identifying structural dampness is crucial because it can cause significant damage to a building, affect the health of its occupants, and reduce the value of the property. The presence of dampness can lead to mold growth, which can cause respiratory problems, allergies, and other health issues. It can also weaken the structure of the building, resulting in costly repairs. Therefore, it is essential to identify the cause of dampness and take the necessary steps to prevent it.

Common Causes of Structural Dampness

Structural dampness can occur due to various reasons. Some of the most common causes include:

  • Condensation: This occurs when warm, moist air comes into contact with cold surfaces such as walls and roofs, causing the moisture to condense and form water droplets. Condensation is a typical cause of dampness in internal walls and can be reduced by improving insulation and thermal performance.
  • Penetration: Rainwater can penetrate the building through cracks, gaps, or faulty roofing, causing dampness in walls and ceilings. Horizontal and vertical dampness can be caused by rain penetration.
  • Rising Damp: This occurs when water from the ground rises up through the walls and floors of the building. Rising damp is most common in older buildings with no damp-proof course or where the existing damp-proof course has failed.
  • Pocket of Moisture: A pocket of moisture can occur when water is trapped within the structure of the building, leading to dampness in specific areas.

The Difference Between Internal and External Dampness

It is essential to differentiate between internal and external dampness to identify the correct cause and prevent further damage. Here are some differences between the two:

  • Internal Dampness: Internal dampness occurs within the structure of the building and is caused by condensation, rising damp, or a pocket of moisture.
  • External Dampness: External dampness is caused by rain penetration and affects the external walls and roof of the building.

The Value of Competence in Identifying Structural Dampness

Identifying the cause of structural dampness requires competence and experience. A qualified surveyor or experienced person can undertake investigations and provide valuable aid in diagnosing the cause of dampness. It is essential to seek professional help to identify the correct cause and take the necessary steps to prevent further damage.

Preventing and Treating Structural Dampness: Key Approaches and Details

One of the key approaches to preventing structural dampness is to provide a damp-proof course through membrane damp proofing. This involves laying a barrier, typically made of synthetic material or slate, between the ground and the concrete, mortar, or plaster of the building’s walls. The membrane acts as a barrier to prevent water from rising up through the pores of the material and entering the building.

Some details to keep in mind when using membrane damp proofing include:

  • The selection of appropriate materials and courses based on the specific needs of the building and the present dampness.
  • The porosity of the materials used in construction, which can affect the effectiveness of the membrane.
  • The layering of the membrane, which should be at least 15 cm above ground level to minimise the risk of moisture entering the building.
  • The diagnosis of existing dampness and the appropriate treatment to fill any gaps or holes in the membrane.

Surface Treatment: Protecting the Exterior

Another approach to preventing dampness is to treat the exterior surface of the building with water-repellent materials. This process involves applying chemical treatments, such as sodium silicate, to the surface of the walls to react with the cement and fill the pores. Waxes can also be used to create a barrier that prevents water from entering the building.

Some details to keep in mind when using surface treatment include:

  • The suitability of the treatment for the specific material used in construction.
  • The principle that the treatment should not block the pores of the material, as this can affect the material’s ability to breathe and lead to further dampness.
  • The need for regular maintenance and reapplication of the treatment to ensure its continued effectiveness.

Cavity Wall Construction: Creating Space for Prevention

A third approach to preventing dampness is to use cavity wall construction, which involves building an outer extra wall to create a cavity between the inner and outer walls. This cavity allows for ventilation and drainage, which can prevent moisture from entering the building.

Some details to keep in mind when using cavity wall construction include:

  • The design of the cavity, which should be at least 50 mm wide to allow for proper ventilation and drainage.
  • The use of appropriate materials for the outer wall, such as modern concrete or synthetic materials, to prevent water from penetrating the wall.
  • The need for careful construction and attention to detail to ensure that the cavity is properly sealed and protected from dampness.

In conclusion, preventing and treating structural dampness requires a thoughtful and comprehensive approach that takes into account the specific needs of the building and the materials used in construction. By using membrane damp proofing, surface treatment, or cavity wall construction, it is possible to protect buildings from the harmful effects of dampness and ensure their longevity and safety.


So, that’s what structural dampness is. It’s a problem with your building’s structure, caused by excess moisture. It can cause mold, health problems, and safety hazards, but it can be prevented and treated. So, don’t ignore the signs and get it checked by a professional. You don’t want to end up with a collapsed building on your hands!

I'm Joost Nusselder, the founder of Tools Doctor, content marketer, and dad. I love trying out new equipment, and together with my team I've been creating in-depth blog articles since 2016 to help loyal readers with tools & crafting tips.