Damp Walls: Rising Damp, Penetrating Damp or a Roof Leak?

A damp patch on a wall tells you there is water where it should not be. It does not tell you where that water came from. Rising damp, penetrating damp, a leaking roof or gutter, a plumbing leak and condensation can all look similar at first glance, and each one needs a completely different fix. Treating the wrong cause is one of the most common ways people waste money on damp.

This article is part of our complete guide to damp proofing and tanking.

The Five Usual Suspects

1. Rising damp

Moisture from the ground is drawn up through the masonry of a wall, usually because the damp proof course (DPC) has failed, was never installed, or has been bridged by soil, paving or plaster. It affects the bottom of walls, typically up to about a metre, and often leaves a horizontal tide mark with white, salty deposits along it. It does not change much with the weather.

2. Penetrating damp

Water moves sideways through an external wall, through cracks in plaster, porous brickwork, failed pointing or gaps around windows. It shows up on the inside of outside walls, can appear at any height, and gets noticeably worse during and after rain, especially wind-driven rain.

3. A roof, gutter or parapet leak

Water from a failed roof, box gutter, flat slab or parapet wall can run down inside a wall cavity or along the top of a wall before appearing lower down. These patches usually start near the top of the wall or the cornice, follow the rain closely, and are often mistaken for penetrating damp. See why box gutters leak.

4. A plumbing leak

A leaking pipe, geyser overflow or shower waste keeps a wall wet regardless of the weather. The damp tends to spread from one point, often near a bathroom, kitchen or geyser, and gets steadily worse rather than coming and going.

5. Condensation

Warm, moist air from cooking, showers and drying laundry condenses on cold surfaces. It causes black mould in corners, behind furniture and around windows, mostly in winter and in rooms with poor ventilation. It is not a building defect, and waterproofing will not fix it.

How to Tell Them Apart

• When does it appear? Only after rain points to the roof, gutters or penetrating damp. All year points to rising damp or plumbing. Mostly in winter points to condensation.
• Where on the wall? A band along the bottom suggests rising damp. Near the ceiling or cornice suggests a roof or gutter leak. A spreading patch around one spot suggests a pipe.
• Is there a tide mark with salts? A horizontal line with white, powdery deposits is a classic sign of rising damp.
• Is it inside or outside walls? Penetrating damp affects external walls. Condensation can affect any cold surface.
• Is there mould? Black mould in corners and around windows is most often condensation.

These clues help narrow it down, but several causes can happen at once. A wall can have rising damp at the bottom and a gutter leak at the top.

Why Getting the Cause Right Matters

Each cause has its own fix. Rising damp needs a damp proofing treatment and often replastering with suitable plaster. Penetrating damp needs the external wall repaired and protected. A roof or gutter leak needs roof waterproofing or the gutter sealed. A plumbing leak needs a plumber. Condensation needs ventilation. Painting over damp with “damp-proof” paint hides the symptom for a while but does nothing about where the water is coming from.

How EcoProof Africa Approaches Damp

We start with a survey. Our team looks at the pattern of the damp, checks the condition of the damp proof course, the external walls, the roof and gutters above, and the ground levels outside, and gives you a written report of what is causing the problem and what needs to be done. If the cause is something outside our work, such as a plumbing leak, we will tell you. See damp surveys and damp proofing in Boksburg and the East Rand.

Where to Go From Here

• What Does Waterproofing Actually Do? Waterproofing versus damp proofing explained.
• How Do I Know If My Roof Needs Waterproofing? If you suspect the roof.
• Waterproofing glossary for terms like DPC and efflorescence.

Not sure what is causing your damp? Get in touch to book a survey.

Frequently Asked Questions

How do I know if I have rising damp?

Typical signs are a horizontal tide mark up to about a metre high on the inside of walls, white salt deposits, plaster that bubbles or crumbles, and damp skirting boards. It is usually present all year rather than only after rain.

Can a roof leak look like rising damp?

Yes. Water from a leaking roof or box gutter can run down inside a wall and appear lower down. The difference is that a roof leak follows the rain and usually starts higher up the wall.

Will damp-proof paint fix my damp wall?

Not on its own. It can hold moisture back for a while, but if the water source is not dealt with, the damp will return, often behind the paint where it does more damage.

Why is there black mould on my walls in winter?

That is usually condensation, caused by moist indoor air meeting cold walls. Better ventilation and reducing indoor moisture are the fix, rather than waterproofing.

What is the difference between waterproofing and damp proofing?

Waterproofing stops liquid water from getting through surfaces exposed to rain, such as roofs and gutters. Damp proofing deals with moisture moving up or through walls, such as rising damp. They solve different problems.

Our roof waterproofing services

EcoProof Africa waterproofs flat roofs, metal roofs, corrugated roofs and asbestos roofs, and can help with gutters and concrete slabs. See all our waterproofing services. We work across Gauteng, including Johannesburg, Randburg, Sandton, Edenvale, Germiston, Boksburg, Benoni, Brakpan, Springs, Bedfordview.