A damp patch on your wall could be three different problems - each with completely different solutions. Before you spend money fixing it, diagnose it properly.
The Three Types of Damp
1. Condensation Damp
The most common cause - often misdiagnosed as something else.
What it is: Moisture from inside your home (cooking, showering, breathing) landing on cold surfaces.
Signs:
- Worst in cold weather
- On or near cold spots (external walls, corners)
- Often accompanied by mould
- Usually near windows or in corners
- Water droplets on windows in morning
- Gets better when heating is on
Location: Usually at high points on walls, in corners, behind furniture against cold walls.
2. Penetrating Damp
Water coming through from outside.
What it is: Rain or groundwater entering through the building fabric.
Signs:
- Worse after rain
- Damp patch grows during/after wet weather
- Shrinks during dry spells
- Often localised to one area
- May have a definite edge or shape
- Might affect the same spot on different floors
Location: Can be anywhere, but often near:
- Windows and doors
- Roofline
- Chimney breast
- External features (pipes, brackets)
- Ground level
3. Rising Damp
The rarest type - often misdiagnosed.
What it is: Groundwater rising up through walls by capillary action.
Signs:
- Tide mark up to about 1 metre high
- Affects ground floor only
- May have salt deposits (white staining)
- Skirting boards may rot
- Consistent pattern along wall
Location: Ground floor only, usually not above 1-1.5 metres.
How to Diagnose Your Damp
Step 1: When Does It Appear?
| Timing | Likely Cause |
|---|---|
| Worst in winter when heating on less | Condensation |
| Worse after rain | Penetrating damp |
| Consistent year-round | Penetrating or rising damp |
| Only in humid rooms (bathroom, kitchen) | Condensation |
Step 2: Where Exactly Is It?
| Location | Likely Cause |
|---|---|
| Corners of external walls | Condensation |
| Behind furniture on external walls | Condensation |
| Below window | Penetrating (check seals) or condensation |
| Chimney breast | Penetrating (roof flashings) or condensation (unventilated flue) |
| Lower wall with tide mark | Could be rising damp |
| Random patch mid-wall | Penetrating damp |
Step 3: What Does It Look Like?
Condensation: Often fuzzy edges, may have mould, paint peeling or wallpaper bubbling.
Penetrating: More defined edge, may be a specific shape, often no mould initially.
Rising: Horizontal tide line, may have white salt deposits, plaster deteriorating.
Testing at Home
The Foil Test
Tape a piece of kitchen foil to the damp wall (seal edges with tape).
After 24-48 hours:
- Moisture on room side of foil = Condensation
- Moisture on wall side of foil = Penetrating or rising damp
The Timing Test
Mark the edge of the damp patch with pencil. Check over days/weeks:
- Grows after rain, shrinks when dry = Penetrating
- Grows in cold weather = Condensation
- Stays consistent = Rising damp or consistent leak
Common Causes by Type
Condensation Causes
- Poor ventilation (especially after modern windows fitted)
- Drying clothes indoors
- Lack of heating
- Single glazing
- Cold spots from thermal bridging
- Blocked air bricks
Penetrating Damp Causes
From above:
- Leaking gutters
- Failed flashings
- Missing/cracked tiles
- Parapet or flat roof problems
Through walls:
- Failed pointing
- Cracked render
- Faulty window seals
- Porous brickwork
- Failed DPC connection
From ground:
- Ground level raised above DPC
- Failed damp course
- Bridged damp course (paving, soil)
Rising Damp Causes
- No damp proof course (old buildings)
- Failed damp proof course
- DPC bridged by external levels
What to Do Next
For Condensation
DIY fixes:
- Improve ventilation (open windows, unblock vents)
- Use extractor fans properly
- Reduce moisture (don't dry clothes on radiators)
- Increase heating (keeps surfaces above dew point)
- Pull furniture away from cold walls
- Consider a dehumidifier
For Penetrating Damp
Investigate:
- Check gutters and downpipes
- Inspect render and pointing
- Look at window seals
- Check roof from ground
- Look for obvious entry points
Then fix the source before treating the symptom.
For Rising Damp
Get a proper survey from an independent surveyor - not a company selling damp treatments. True rising damp is much rarer than companies suggest.
Often misdiagnosed as rising damp:
- Condensation at low level
- Penetrating damp from ground level
- Hygroscopic salts holding moisture
- Plumbing leaks
Warning: Damp Company Sales Tactics
Free "damp surveys" from companies selling treatments often result in:
- Chemical DPC injection you don't need
- Re-plastering that doesn't fix the cause
- Expensive work that doesn't solve the problem
Red flags:
- "Free survey" that recommends their products
- Pressure to decide quickly
- Focus on treatment not cause
- Diagnosed without proper investigation
Better approach: Pay for an independent surveyor (RICS or CABE) who won't sell you treatments.
When to Get Professional Help
Get a surveyor if:
- You can't identify the cause
- Damp is extensive or worsening
- Structural damage is occurring
- You're buying a property with damp
Get a builder/handyman if:
- You've identified the cause
- It's clearly a maintenance issue (gutters, pointing)
- You need repair work done
Damp patch puzzling you? I can help diagnose the cause and suggest solutions. Call 01392 964094 or get a quote.
Sam Hembury
Sam is the founder of Hembury Contracting, providing professional handyman services across Exeter and Devon. With years of experience in property maintenance, he shares practical tips to help homeowners tackle common tasks.
