How to Identify and Fix Penetrating Damp in Your Home

Penetrating damp is a common issue in properties of all ages, often caused by external moisture seeping through walls, roofs, or structural defects. If left untreated, it can lead to serious structural damage and mould growth, affecting both the integrity of your home and your health.

What is Penetrating Damp?

Unlike rising damp, which moves upward from the ground, penetrating damp occurs when water enters a building horizontally through porous materials such as brick, stone, or mortar. It is typically caused by defective masonry, blocked gutters, leaking roofs, or cracks in external walls.

Signs of Penetrating Damp

Identifying penetrating damp early can prevent costly repairs. Look out for these key indicators:

• Damp patches on internal walls that worsen after rainfall

• Mould growth in specific areas, particularly on walls and ceilings

• Peeling wallpaper and blistering paint

• Rotting wood, especially in skirting boards, window frames, and floorboards

• Musty odours indicating trapped moisture

What Causes Penetrating Damp?

Several factors contribute to penetrating damp, including:

• Damaged Brickwork & Pointing – Crumbling mortar and cracked bricks allow water to penetrate walls.

• Blocked or Leaking Gutters – Water overflowing from gutters can soak exterior walls, leading to damp penetration.

• Roof Defects – Broken or missing tiles, damaged flashing, or poor roof maintenance can allow water ingress.

• Porous or Non-Breathable Paints – Some modern paints trap moisture inside walls, preventing natural evaporation.

• External Ground Levels – If soil or paving is too high against an external wall, it can direct moisture inside.

How to Treat and Prevent Penetrating Damp

1. Repair External Damage

• Repoint damaged brickwork using lime mortar, which allows walls to breathe.

• Replace cracked or missing roof tiles and repair flashing.

• Seal external wall cracks and repaint with a breathable, water-repellent coating.

2. Maintain Your Guttering and Roof

• Regularly clear gutters of debris to prevent water overflow.

• Ensure downpipes and drains are functioning properly.

• Install gutter guards to reduce blockages.

3. Improve Drainage Around the Property

• Lower external ground levels if they are above internal floor levels.

• Install a French drain or a damp-proof course (DPC) to redirect moisture away.

• Ensure proper land grading around the property to direct water away from the foundations.

• Use gravel or permeable paving to improve drainage and prevent water pooling near the walls.

4. Increase Ventilation

• Improve airflow with trickle vents, extractor fans, or dehumidifiers.

• Avoid blocking air bricks or vents, especially in period properties.

• Open windows regularly to reduce excess moisture buildup.

• Install Positive Input Ventilation (PIV) systems to help circulate air and prevent condensation.

5. Apply Waterproofing Treatments

• Use high-quality waterproof masonry cream on external brickwork to repel rainwater while allowing walls to breathe.

• Install an additional cavity wall membrane to add another layer of protection against moisture ingress.

• Treat wooden surfaces with fungicidal and damp-resistant coatings to prevent rot and decay.

When to Seek Professional Help

If penetrating damp persists, consult a damp proofing specialist or an RICS Chartered Surveyor. They can conduct a thorough damp survey and recommend appropriate long-term solutions tailored to your property’s needs.

Final Thoughts

Penetrating damp can cause serious damage if ignored, but early identification and proper treatment can save you time and money. By maintaining your property’s exterior, improving drainage, and ensuring adequate ventilation, you can prevent moisture ingress and protect your home.

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