Cellars and basements are naturally more vulnerable to moisture than many other areas of a property.
If you've noticed wet walls, peeling paint, white salt deposits or a persistent musty smell below ground, you may be wondering:
Why is my cellar so damp?
The answer often comes down to one important factor.
Your cellar is surrounded by ground.
This means the walls and floor can be exposed to moisture within the surrounding soil, creating very different conditions to a typical room above ground level.
However, not every damp cellar has the same problem.
Quick Answer
A damp cellar or basement may be caused by groundwater, lateral moisture penetration, defective drainage, plumbing leaks, condensation or the absence or failure of an appropriate waterproofing system.
Because below-ground structures are exposed to different moisture conditions, identifying the source and behaviour of the water is essential before recommending remedial work.
Why Are Cellars So Prone To Damp?
A typical external wall is exposed to the weather on one side and the internal environment on the other.
A cellar wall is different.
Part or all of the wall may be positioned below external ground level.
The surrounding soil can retain moisture, particularly following prolonged or heavy rainfall.
Where there is no effective barrier or waterproofing system, moisture may move through the building fabric.
1. Water Penetrating Through Cellar Walls
Moisture can enter through below-ground walls.
This is sometimes referred to as lateral water penetration because moisture is moving through the wall from the surrounding ground.
Common signs include:
- Damp patches on cellar walls
- Wet masonry
- Flaking paint
- Deteriorating plaster
- Salt deposits
- Musty smells
The severity of the problem may change depending on rainfall and ground conditions.
2. Hydrostatic Pressure
Water within the ground can place pressure against below-ground structures.
This is known as hydrostatic pressure.
Where groundwater levels rise, water may be forced against walls and floors.
Weaknesses within the structure or waterproofing system can become potential routes for moisture ingress.
3. No Existing Waterproofing System
Many older cellars were never designed to be dry, habitable rooms.
Historically, cellars may have been used for storage rather than as bedrooms, offices or living spaces.
If the intended use of the cellar changes, the existing building structure may not provide the level of moisture protection required for a modern internal environment.
4. Failed Or Deteriorated Tanking
Some cellars have previously been treated with a tanking or barrier system.
Inappropriate materials, poor preparation or defects within an existing system may result in moisture becoming visible again.
Simply applying another coating over the affected wall may not resolve the underlying issue.
The existing system and condition of the substrate should be assessed before further waterproofing work is specified.
5. Defective External Drainage
Poor drainage around a property can increase the amount of water held within the surrounding ground.
Common issues may include:
- Defective drains
- Leaking downpipes
- Overflowing gutters
- Poor surface drainage
- Water collecting against the building
These factors can increase moisture exposure around below-ground walls.
6. Plumbing Leaks
Not every wet cellar is caused by groundwater.
Leaking internal pipework, incoming water mains and drainage defects can introduce moisture into a basement or cellar.
A localised damp area or sudden change in moisture conditions may require further investigation.
7. Condensation In Cellars
Cellars are often naturally cooler than the rest of the property.
When warm, moisture-laden air enters a colder basement environment, condensation can form on cold walls, pipes and other surfaces.
Poor ventilation can make the problem worse.
This means a cellar may be affected by condensation, water penetration or a combination of different moisture sources.
What Are The Signs Of A Damp Cellar?
Common warning signs include:
- Wet or damp walls
- Peeling paint
- Blown plaster
- Salt deposits
- Musty odours
- Mould growth
- Damp flooring
- Water collecting after rainfall
- Rusting metalwork
- Decaying timber
The location and pattern of these symptoms can provide useful information when investigating the cause.
What Are The White Salts On My Cellar Wall?
White deposits are commonly seen on damp cellar walls.
Moisture moving through masonry can carry soluble salts towards the surface.
As moisture evaporates, salts may remain behind.
However, visible salts alone do not tell you exactly what is causing the damp.
The wider moisture pattern and building construction should still be investigated.
Can I Just Paint Over A Damp Cellar Wall?
Painting over a damp cellar wall is unlikely to provide a long-term solution if moisture is continuing to enter the structure.
Decorative coatings may begin to:
- Bubble
- Flake
- Peel
- Discolour
Before redecorating, the source of moisture should be understood.
What Is Cellar Tanking?
Cellar tanking is a form of waterproofing designed to resist moisture entering through below-ground walls and floors.
A Type A barrier protection system uses a waterproofing material applied to the structure to create a barrier against water ingress.
At Weather Wise Solutions, appropriate below-ground waterproofing specifications may include specialist systems such as Remmers MB 2K where suitable for the property and proposed remedial design.
However, tanking should not simply be recommended because a cellar feels damp.
The structure, moisture conditions and intended use of the space should first be assessed.
Are All Basement Waterproofing Systems The Same?
No.
Different waterproofing approaches may be considered depending on the property.
The correct specification can depend on:
- The building structure
- Ground conditions
- Water pressure
- Intended use of the space
- Existing defects
- The required internal environment
This is why a survey and appropriate waterproofing specification are important.
What We See During Cellar Damp Surveys
One of the most common misconceptions is that every damp cellar simply needs tanking.
Sometimes waterproofing is appropriate.
In other cases, defective drainage, a plumbing leak or condensation may be contributing to the problem.
We also inspect cellars where several moisture sources are present at the same time.
A damp cellar is a symptom. Understanding how water is entering or forming within the space is the first step towards designing the correct solution.
Can A Damp Cellar Be Made Dry?
In many cases, a damp cellar can be significantly improved or waterproofed for its intended use.
However, the correct approach depends on the property.
A cellar being used for basic storage may have very different requirements to a basement being converted into a bedroom, office or living area.
The intended use of the space should always form part of the waterproofing specification.
About The Author
Written by Brandon Parry
Brandon Parry is an FODCS Certified Surveyor and holds the Level 3 Award in Damp, Mould and Condensation in Buildings. He has a particular interest in historic buildings, traditional construction and understanding how moisture interacts with different building materials.
Technical Review
Reviewed by Neil Hudson
Neil Hudson is a Director of Weather Wise Solutions | CSTDB | ABBE Level 3 Award in Dampness in Buildings | FODCS Certified Surveyor.
Neil has a strong interest in buildings, construction and the diagnosis of moisture-related defects within properties.
Contributor
John Darbyshire
John Darbyshire is part of the Weather Wise Solutions surveying team, supporting homeowners with the investigation of damp and moisture-related concerns within their properties.
Frequently Asked Questions
Why are my cellar walls wet?
Below-ground walls can be exposed to moisture within the surrounding soil. Groundwater, drainage defects, condensation and leaks may all contribute.
Is a damp cellar normal?
Older cellars were not always designed to provide a dry, habitable internal environment. However, persistent or worsening moisture should be investigated.
Will a dehumidifier dry out my cellar?
A dehumidifier may help manage humidity and condensation, but it will not stop water penetrating through the building structure.
Does every damp cellar need tanking?
No. The source of moisture, building construction and intended use of the cellar should be assessed before waterproofing is specified.
What is cellar tanking?
Cellar tanking is a waterproofing approach that creates a barrier designed to resist water ingress through below-ground walls or floors.
Why does my cellar get wetter after heavy rain?
Rainfall can increase moisture levels within the surrounding ground. Defective drainage or water penetration through the building structure may then become more noticeable.
Can I convert a damp cellar into a room?
Potentially, but the proposed use of the space and waterproofing requirements should be carefully assessed before conversion work begins.
References & Further Reading
- UK Government, Approved Document C: Site Preparation And Resistance To Contaminants And Moisture – https://www.gov.uk/government/publications/site-preparation-and-resistance-to-contaminates-and-moisture-approved-document-c
- British Standards Institution – https://www.bsigroup.com
- Historic England – https://historicengland.org.uk
- Remmers UK – https://www.remmers.co.uk
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