Penetrating damp is when rainwater or moisture enters a building from the outside through defects in the walls, roof, or around windows and doors. It happens when external moisture, such as driving rain, seeps into the structure and moves through the building’s fabric, eventually appearing on internal walls or ceilings.
This form of damp is common in older properties and homes with damaged gutters, cracked brickwork, or poor sealing. Unlike rising damp, which travels upward from the ground, penetrating damp moves horizontally through the walls.
FAQ
1. What is penetrating damp?
Penetrating damp occurs when rainwater or moisture enters a building from the outside, seeping through the walls, roof, or around windows and doors.
It’s caused by defects in the property’s exterior — such as cracked brickwork, blocked gutters, or poorly sealed frames — allowing water to travel through the structure and appear as damp patches inside.
Unlike rising damp (which moves upward from the ground), penetrating damp moves horizontally through walls and ceilings, especially during or after rainfall.
2. What causes penetrating damp?
The most common causes include:
- Blocked or damaged gutters and downpipes that overflow onto walls
- Cracks in brickwork or render that let rain penetrate
- Broken or missing roof tiles allowing water to seep through
- Poorly sealed windows or doors that let rain in during storms
- Defective plumbing, such as internal leaks mimicking external damp
💡 Tip: Regular maintenance can prevent most of these issues before they cause long-term damage.
3. What are the signs of penetrating damp?
You might notice one or more of the following:
- Damp patches on walls or ceilings that worsen after rain
- Peeling paint or bubbling plaster
- Musty smells or a cold, damp feeling in rooms
- Mould or mildew forming on walls
- Moss or algae growth on exterior walls
- Crumbling or flaking brickwork (spalling)
- Visible water stains running down internal walls
These symptoms often appear on the side of the property most exposed to wind and rain.
4. Why is penetrating damp a problem?
If left untreated, penetrating damp can lead to:
- Structural weakening of brickwork, mortar, and timber
- Mould and mildew growth, which affect air quality and health
- Damage to interior finishes, such as paint, plaster, and wallpaper
- Increased repair costs as moisture spreads deeper into the property
Over time, dampness can also attract pests and contribute to wood rot, particularly in roof timbers or joists.
5. Can penetrating damp make you ill?
Yes. Damp and mould release spores and allergens into the air that can cause or worsen:
- Asthma
- Allergies
- Coughing or sinus problems
- Skin irritation or eczema
Those most at risk include young children, the elderly, and anyone with respiratory conditions.
Treating damp promptly helps maintain both a healthy home and healthy occupants.
6. How can I tell if it’s penetrating damp or rising damp?
Here’s how to tell the difference:
- Penetrating damp appears on upper walls, ceilings, or around windows — and is worse after rain.
- Rising damp appears at the base of walls (up to about one metre high) and comes from ground moisture moving upwards.
If you’re unsure, a professional damp survey can confirm the source using moisture meters and thermal imaging.
7. How do you fix penetrating damp?
The treatment depends on the cause but typically involves:
- Clearing or repairing gutters and downpipes
- Repointing cracked brickwork or render
- Replacing damaged roof tiles or flashing
- Resealing or refitting windows and doors
- Fixing any plumbing leaks
- Applying a breathable waterproof coating or damp-proof treatment to external walls
8. How can I prevent penetrating damp in future?
Prevention tips:
- Clean and check gutters regularly
- Inspect your roof annually for missing tiles or damage
- Repoint brickwork and repair cracks early
- Ensure all windows and doors are properly sealed
- Keep exterior walls painted or rendered with weatherproof materials
- Schedule routine property maintenance — especially before winter
🛠️ Consistent upkeep is far cheaper than repairing damage once damp has set in.
9. When should I book a professional damp survey?
Book a survey if you notice:
- Damp or mould that keeps returning after cleaning
- Discoloured patches on walls or ceilings
- Musty smells that linger after rain
- Peeling paint or bubbling plaster
A professional damp survey identifies whether the issue is penetrating damp, rising damp, condensation, or plumbing-related — ensuring the correct treatment is applied first time.
10. Who can fix penetrating damp in London?
Damp and Mould Solutions Ltd are London specialists in diagnosing and treating penetrating damp.
We offer expert surveys, repairs, and long-term solutions backed by a 20-year guarantee.
📞 Call 020 4542 6116
📧 info@dampandmouldsolutions.co.uk
🌐 www.dampandmouldsolutions.co.uk