Penetrating Damp Treatment Specialists
Penetrating damp starts with water getting in from outside, through a defect in the building. We trace exactly where it is entering, fix it at the source, and make good inside, so the damp stops instead of coming back.
- ✓ We find the source: the entry point, not just the damp patch you can see
- ✓ Fixed at the cause: repairs and weatherproofing to stop the water getting in
- ✓ 20-year guarantee: on our damp proofing works, with an insurance-backed option on request
Source-Traced
We locate exactly where water is entering before we quote any work.
Certified Surveyors
FODCS certified and members of the Federation of Damp.
20-Year Guarantee
On our damp proofing works, with an insurance-backed option on request.
Rated by Customers
Trusted by homeowners with 5-star reviews.
What Is Penetrating Damp?
Penetrating damp is moisture that travels horizontally into a building from outside, through a defect in the walls, roof or openings, rather than rising up from the ground. It is sometimes called lateral damp.
Unlike rising damp, which is limited to the bottom of ground-floor walls, penetrating damp can appear at any height and on any floor, wherever the water is getting in. And unlike condensation, which forms on cold internal surfaces, penetrating damp is driven by water coming through the structure from the outside.
The tell-tale clue is timing: penetrating damp almost always gets noticeably worse during and after heavy or driving rain, then eases in dry spells. If the entry point is not found and fixed, the damp patch simply returns every time it rains.
Signs of Penetrating Damp
Penetrating damp shows up differently depending on where the water is getting in and how long it has been happening. The common signs are:
If the damp clearly tracks the weather, getting worse when it rains, it is far more likely to be penetrating damp than condensation. Our free 60-second damp checker can help you narrow it down.
What Causes Penetrating Damp (and How We Fix Each One)
Penetrating damp is always a symptom of a defect in the building fabric. Finding which one is the whole job, because the same damp patch can have very different causes. These are the ones we find most often:
Failed pointing & cracked brickwork
When mortar joints erode or crack, rain soaks straight into the wall. This is the single most common cause we see on older masonry.
The fix: rake out and repoint with a suitable mortar, repair cracked bricks, and weatherproof the elevation where exposure is high.
Cracked or blown render
Cracks in render let water in behind it, where it gets trapped against the wall and cannot dry out, spreading the damp inside.
The fix: cut out and renew failed render, ideally with a breathable system so the wall can dry, then redecorate.
Leaking or blocked gutters & downpipes
Overflowing or split guttering pours water down one part of the wall, saturating it. A classic cause of a damp patch that is always in the same spot.
The fix: clear, realign or replace the guttering and downpipes so rainwater is carried away from the wall.
Roof defects
Slipped or cracked tiles, failed flashing and blocked valleys let water into the roof space and down into ceilings and the tops of walls.
The fix: identify the entry point and repair the tiles, flashing or valley so the roof sheds water properly again.
Defective window & door seals
Perished sealant, failed sills and missing drip details let rain run in around frames, showing as damp below or beside windows.
The fix: renew seals and mastic, repair or replace sills, and reinstate the weathering details that throw water clear.
Chimney defects
Cracked flaunching, failed flashing and an uncapped flue let water into the stack, often showing as damp on the chimney breast inside.
The fix: repair flashing and flaunching, fit a cap or vent where needed, and address the salts left in the masonry.
Bridged or failed cavity
Mortar dropped in the cavity, debris on wall ties, or unsuitable cavity insulation can carry water across the gap to the inner wall.
The fix: clear the cavity, deal with bridging, and where needed weatherproof the outer leaf to reduce saturation.
Exposed solid walls
Single-skin and solid walls on weather-facing elevations can become saturated in driving rain, with no cavity to stop the water reaching inside.
The fix: apply a breathable masonry protection or weatherproofing system, and improve external rainwater detailing.
Penetrating Damp vs Rising Damp vs Condensation
Getting this right is the whole point of a survey, because each one needs a completely different fix:
| Penetrating Damp | Rising Damp | Condensation | |
|---|---|---|---|
| Where it appears | Any wall or ceiling, near a defect | Ground-floor walls only | Cold spots, corners, windows |
| How high | At any height, on any floor | Up to about a metre | Anywhere, often up high |
| Timing | Worse during and after rain | Fairly constant year round | Worse in cold, still weather |
| Main cause | A defect letting water in | No or failed damp proof course | Humid air on cold surfaces |
| The fix | Repair the defect, then make good | New damp proof course and replaster | Ventilation and insulation |
Damp is often a mix of more than one of these. A damp survey tells you exactly what you are dealing with.
How We Diagnose & Treat Penetrating Damp
Because penetrating damp is a symptom, the diagnosis is everything. Treat the patch without finding the entry point and it always returns. Our process:
External inspection
We examine the elevation above and around the damp: pointing, render, gutters, roof, flashing, sills and ground levels.
Internal survey
Moisture meter readings and thermal imaging map the wet area and confirm the pattern matches water ingress, not rising damp or condensation.
Fix at the source
We repair the defect, repointing, render, guttering, roof, seals or weatherproofing, so water can no longer get in.
Make good inside
Once the wall can dry, we renew damaged plaster with a suitable system and leave it ready to redecorate.
Our remedial damp proofing works are backed by a written 20-year guarantee, with an insurance-backed guarantee available as an option on request. The right repair depends entirely on the cause, which is why every job starts with a survey and a fixed-price quote, with the survey fee deducted from the cost of the works if you go ahead.
What Our Customers Say
★★★★★
"Very good service and found a leak in our roof and made it easier to relay that information to the roof guy."
John Hamlin · Trustpilot review★★★★★
"We contacted Advanced Damp to help us with a damp issue on one of our windows. Communication was prompt, easy, friendly and professional. The assessment was carried out thoroughly and competently by Lionel and the report was comprehensive."
Gaby · Trustpilot review★★★★★
"Noticed a nasty damp patch in my house and panicked! Advanced Damp came to the rescue. Their surveyor was super knowledgeable and put me at ease. Now my house is dry again, thanks to their top-notch service."
G G · Google reviewYour Penetrating Damp Surveyor
Sam Fitzgerald
Founder & SurveyorSam is the founder of Advanced Damp and a working damp and structural waterproofing surveyor with over 12 years of experience. FODCS certified and a member of the Federation of Damp, he and his team trace water ingress in homes of every age and put it right at the source.
Meet the full team →Where We Work
We treat penetrating damp across London, the South East and the Midlands. Find your area:
Penetrating damp is part of our wider damp proofing service.
Penetrating Damp FAQs
What does penetrating damp look like?
It usually appears as a damp patch or brown-edged stain on a wall or ceiling that gets worse after rain, often with blown plaster, peeling paint and localised mould around it. It tends to be in one specific area, directly inside wherever the water is getting in.
How do you tell penetrating damp from rising damp or condensation?
Timing and location are the giveaways. Penetrating damp can be at any height and gets worse when it rains. Rising damp is only on ground-floor walls, up to about a metre, and stays fairly constant. Condensation forms on cold surfaces and corners and is worse in cold, still weather. A survey with moisture meters and thermal imaging confirms which it is.
How do you treat penetrating damp?
You fix the defect that is letting water in, whether that is repointing, renewing render, repairing gutters or the roof, resealing windows or weatherproofing an exposed wall, then let the wall dry and renew any damaged plaster. There is no single treatment, because it depends entirely on how the water is getting in.
How do you treat penetrating damp on internal walls?
The lasting fix is almost always on the outside, stopping the water at its entry point. Once that is done and the wall has dried, the damaged internal plaster is removed and replaced with a suitable system. Treating only the inside, without fixing the external cause, just hides the problem until it returns.
Will penetrating damp go away on its own?
No. The defect letting water in does not repair itself, so the damp returns every time it rains and steadily gets worse, damaging plaster, decoration and eventually timber. The sooner the source is found and fixed, the cheaper and smaller the repair.
Does buildings insurance cover penetrating damp?
It depends on the cause. Damp resulting from a sudden, one-off event such as storm damage may be covered, but damp caused by gradual wear, lack of maintenance or an ageing roof or pointing is usually treated as a maintenance issue and excluded. It is always worth checking your own policy wording.
How much does penetrating damp treatment cost?
It varies widely because the work depends on the cause, from a straightforward gutter repair to repointing a whole elevation or renewing render. We give a fixed-price quote after the survey so you know the cost up front, and the survey fee is deducted from the works if you proceed.
Related Services & Information
Find Where the Damp Is Getting In
Book a survey and we will trace the source of the water ingress and set out exactly how to stop it, with a fixed-price quote and the fee deducted from any treatment you proceed with.