If you've noticed damp patches appearing after heavy rainfall, you're not alone.
One of the most common questions we receive is:
"Why does my wall only get damp when it rains?"
Unlike condensation, which is caused by moisture within the home, damp that appears after rainfall is often linked to defects that allow water to enter the building from outside.
This type of moisture problem is commonly known as penetrating damp.
Quick Answer
If a wall becomes damp after rainfall, it may be caused by penetrating damp. This occurs when water enters a property through defects such as damaged brickwork, cracked render, defective pointing, leaking gutters, roof problems or failed seals around windows and doors.
What Is Penetrating Damp?
Penetrating damp occurs when water enters the building fabric from outside.
Unlike rising damp, which moves upwards from the ground, penetrating damp can affect walls, ceilings and chimney breasts at almost any level.
Common Causes Of Penetrating Damp
Some of the most common causes include:
- Damaged brickwork
- Defective pointing
- Cracked render
- Leaking gutters and downpipes
- Roof defects
- Failed window or door seals
- Blocked cavities
- Chimney defects
Signs Of Penetrating Damp
Look out for:
- Damp patches after rainfall
- Peeling paint or wallpaper
- Water staining
- Salt deposits
- Mould growth in affected areas
- Damp chimney breasts
How Is It Different From Condensation?
Condensation is created by moisture inside the home.
Penetrating damp is caused by water entering from outside.
Although both can leave similar signs, the underlying causes are very different.
What We See During Surveys
Many homeowners assume all damp is caused by condensation.
However, when damp consistently appears after rain, external defects are often responsible.
Identifying where water is entering the building is essential before deciding on any remedial work.
Can Penetrating Damp Be Fixed?
Yes, in many cases.
The first step is identifying the point of water ingress.
Repairs may involve:
- Repointing masonry
- Repairing render
- Fixing gutters or downpipes
- Replacing damaged roof coverings
- Improving external weatherproofing
The correct solution depends on the source of the moisture.
About The Author
Written by Brandon Parry
Brandon Parry is an ABBE Level 3 Award in Dampness in Buildings holder and FODCS Certified Surveyor with a particular interest in traditional buildings, masonry defects and external moisture ingress.
Technical Review
Reviewed by Aaron Worrall
Aaron Worrall is a Director of Weather Wise Solutions, CSTDB-qualified surveyor, ABBE Level 3 Award in Dampness in Buildings holder, FODCS Certified Surveyor, Tech.DEW qualified professional and Advanced City & Guilds Mould Remediation specialist.
Contributor
Peter Potts
Peter Potts is an ABBE Level 3 Award in Dampness in Buildings holder and FODCS Certified Surveyor who enjoys helping homeowners understand the causes of damp and the most appropriate remedial solutions.
Frequently Asked Questions
Can rain cause damp walls?
Yes. Water can enter through defects in the external fabric of a building.
Is penetrating damp serious?
If left unresolved, penetrating damp can lead to internal damage, mould growth and timber decay.
How do I know if my damp is caused by rain?
If damp appears or worsens after rainfall, penetrating damp may be the cause.
Can gutters cause damp?
Yes. Leaking or blocked gutters are a common cause of penetrating damp.
Will repainting fix penetrating damp?
No. Unless the source of water ingress is repaired, the problem is likely to return.
References & Further Reading
- Historic England – https://historicengland.org.uk
- Chartered Institute of Building – https://www.ciob.org
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If you're experiencing damp after heavy rain, our qualified surveyors can identify the source of water ingress and recommend the most appropriate solution.