Damp problems in homes are more than just an inconvenience—they can weaken structures, encourage mould growth, and reduce property value. Penetrating damp and rising damp are two of the most common types, and each requires a different approach to treatment.
Penetrating damp is caused by rainwater seeping through porous brickwork or external defects. Rising damp, however, is due to moisture travelling upwards from the ground because of a failed damp proof course (DPC).
Spotting the warning signs early can help avoid expensive repairs. In this guide, we’ll explain how to identify, diagnose, and treat both forms of damp so you can protect your home.
What is Penetrating Damp?
Penetrating damp occurs when moisture enters a property due to porous brickwork or faults in external walls, roofs, or windows. Unlike rising damp, which moves vertically, penetrating damp spreads horizontally through walls, plaster, and timber.
It can affect any level of a property and is common in older homes. The main causes include:
- Porous brickwork – The outer surface of bricks absorbs rainwater. When frozen, this expands and cracks the brick from the inside, allowing more moisture in.
- Leaky roofs – Broken tiles or damaged flashing let rain in.
- Faulty gutters and downpipes – Overflowing water soaks external walls.
- Cracked brickwork or render – Gaps provide entry points for moisture.
- Cavity wall insulation issues – If incorrectly installed, insulation traps moisture, helping damp migrate across wall cavities.
Penetrating damp often worsens after heavy rainfall, leading to crumbling plaster, rotting wood, and persistent mould.
What is Rising Damp?
Rising damp happens when groundwater is absorbed through porous walls due to a missing or damaged damp proof course (DPC). The moisture travels upwards through capillary action, reaching a height of up to 1.2 metres.
Modern homes have a DPC, but damp occurs if:
- The DPC has failed or been bridged.
- External ground levels are too high, pushing water against walls.
- The home lacks a DPC (common in older properties).
Unlike penetrating damp, rising damp remains consistent year-round, as it is linked to ground moisture rather than rainfall. Signs include tide marks, crumbling plaster, and white salt deposits (efflorescence) on walls.
Source of Moisture
The key difference between penetrating damp and rising damp lies in where the moisture comes from.
- Penetrating damp is caused by rain soaking into porous brickwork or entering through external defects. In cavity walls, damp can migrate across wall ties, insulation, or debris inside.
- Rising damp happens when groundwater is drawn upwards through walls due to a compromised DPC.
Understanding the source of moisture helps homeowners choose the right treatment and prevent further damage.
Location of Damp
Where damp appears can help determine whether a property has penetrating damp or rising damp.
- Penetrating damp can appear anywhere on a wall, often at higher levels, near ceilings, windows, or mid-wall areas. It may affect both internal and external walls.
- Rising damp is limited to ground floors and usually stops at 1.2 metres above ground level. It is most visible along skirting boards, plaster, and lower wall sections.
Identifying damp locations can help homeowners diagnose the issue and find the right solution.
Appearance
The visual signs of damp can help distinguish between penetrating damp and rising damp.
- Penetrating damp appears as irregular damp patches that darken and spread after rainfall. If left untreated, it causes peeling paint, mould growth, and crumbling plaster.
- Rising damp leaves distinct tide marks (up to 1.2 metres high). Affected walls often have blistering paint, crumbling plaster, and white salt deposits (efflorescence).
Signs of Damage
Both penetrating damp and rising damp can cause noticeable damage, but their effects differ:
- Penetrating damp leads to peeling paint, blistering wallpaper, and rotting woodwork. If ignored, it may cause serious structural issues, especially in timber-framed properties.
- Rising damp affects interior walls, damaging skirting boards, plaster, and flooring. Salt deposits from rising moisture can further weaken wall surfaces, requiring repairs.
Smell
A musty smell is a common warning sign of damp, though the cause varies:
- Penetrating damp often smells stronger after heavy rain, as water seeps in and encourages mould growth.
- Rising damp produces a persistent musty smell, often linked to mould growth and rotting timber in skirting boards or flooring.
Both types of damp can cause an unpleasant indoor atmosphere, making early intervention essential.
Seasonal Effects
Damp issues may worsen depending on the season:
- Penetrating damp is worse in wet weather, as heavy rainfall increases water penetration through porous walls or structural defects.
- Rising damp remains constant year-round, since it is caused by ground moisture rather than rain.
Treatment Methods
Rising Damp Solutions
- Install or repair a damp proof course (DPC) – A working DPC is essential to prevent moisture from rising.
- Replace damaged plaster – Moisture-damaged walls should be replastered with a salt-resistant mix after treatment.
Penetrating Damp Solutions
- Apply a waterproofing wall coating – The most effective solution is a microporous water-repellent treatment, which prevents rain penetration while allowing walls to breathe.
- Repair external defects – Fix leaking gutters, cracked brickwork, and damaged roofs to stop rainwater entering.
- Check cavity wall insulation – Incorrectly installed insulation can trap moisture and transmit damp inside, sometimes requiring removal.
Book a Free Damp Survey Today
Damp problems won’t go away on their own—and waiting can lead to higher repair costs and further structural damage.
If you’ve spotted signs of penetrating damp or rising damp, don’t take chances. Book a free damp survey with Home Energy Save GB today. Our specialists will identify the cause and recommend long-term solutions to protect your home. Call us now or request your free assessment online!