What Is Penetrating Damp?

What Is Penetrating Damp?
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You may have heard of this phenomenon, or even experienced it in your home, but what is penetrating damp exactly?

How does it differ from other types of damp, what causes it, what problems does it create, how can you spot it, and what can you do about it?

Here, the Property Road team will answer these questions and use our experience to provide some useful tips on how to deal with penetrating damp.

What causes penetrating damp?

Penetrating damp, which is referred to as rain penetration by some people, is caused by water entering a property either through an external wall defect, or a crack.

It’s a fact of life that the building materials we use in the UK, such as brick, are porous. That means they soak up the rain – which then leads to a wall becoming saturated with penetrating damp.

When we experienced penetrating damp, we were surprised at just how even the smallest of entry points for water can lead to significant internal damp problems.

Several factors can lead to this problem, including:

Rain penetration through cavity walls

This issue is not just restricted to single-skin walls, since poorly installed cavity wall insulation and wall-ties can also lead to water ingress.

This was our main problem when cracks in our house render led to several damp patches appearing around our property.

Window & door frames

Damp penetrating via windows and doors
Damp entering our property via the windows and doors

These are a common point of ingress for moisture, so watch out for general damage, a lack of weather protection and cracks as these will let water in.

We’ve experienced this problem too. In our case, our home is south facing and very exposed to the elements. Over time, that led to the silicone sealant around our windows and doors to become brittle and crack.

Even just a slight crack around the sealant can cause water to enter your home.

Defective pointing and porous bricks

Wet Bricks
Some of our bricks were absolutely soaking!

These are relatively easy fixes – you can repoint a wall easily or get a builder in to do the work for you.

Our extension was built in the 1980s using a very porous brick, this meant we also experienced penetrating damp through otherwise perfectly healthy bricks.

Luckily for us, it was a cavity wall and the water never bridged into our home. However, wet brickwork does lead to crumbling of bricks and mortar over time which can eventually cause more problems.

While we haven’t yet resolved this issue, we plan on having the whole extension rendered with a waterproof render to prevent further water penetration and protect the brickwork.

Damaged or inadequate roof coverings

Look for damaged pointing or flashing – and missing or cracked roof tiles.

This is another source of penetrating damp that we’ve personally experienced. Loose ridge tiles and defective flashing on our chimney stacks was leading to water entering our roof space.

Luckily, this is one of the easier fixes and we could easily get a roofer to repair both problems in just a days work.

Poorly maintained gutters and downpipes

This also extends to the drains as rainwater can collect against the brickwork when drains are blocked. Moreover, a broken or blocked drain can cause water to collect or fall in unusual areas to cause mould and dampness.

Also, prolonged periods of wet weather can exacerbate the issue, particularly in buildings with weather-facing walls.

If you live anywhere with poor weather conditions, then it won’t matter whether you live in a new or old building, you can still suffer with penetrating damp.

Guttering just short of roof
Our guttering stopped just short of the end of the roof!

It’s also worth checking your guttering has been installed properly. Our property had guttering which finished a couple of inches short of the roof, leading to excessive damp issues in the corner of the building.

When we had a couple of windows replaced, we took the opportunity to also get the guttering extended slightly to cover the full length of our roof and the problems were resolved immediately.

Our experience with penetrating damp

In 2021 we bought a rural property that was built in the 1800’s with solid walls, with a more recent cavity wall extension added in the 1980’s.

While the building had recently been part-renovated, we quickly found that water doesn’t need much of an invite to cause problems.

Problem #1: Cracked Rendering

The first thing we noticed were cracks to the external rendering that ran between the upper and lower windows. These were relatively small cracks but the surrounding render had darkened which was a dead giveaway that water was penetrating behind the render.

We also had small cracks running alongside the windows, caused by two different materials meeting and one shrinking over time.

Repairs To Our Cracked Rendering
Repairs to our cracked rendering to stop penetrating damp

While it wasn’t immediately obvious internally, we did eventually start to find damp patches appearing along the floor level. These were mostly centered around the sockets, since the wall will have been hollowed out to allow the wires and sockets to be added.

Of course, water always follows the path of least resistance and so these ‘cavities’ were the first to show the signs of our penetrating damp issues.

As our cracked render was caught early, it was easy enough for a local tradesperson to repair. They simply chipped off the old render along the crack, added a mesh to help prevent the crack re-opening, then added new render and gave it a lick of paint.

First problem solved!

Problem #2: Failing Silicone

Lean To Before & after
We added lead flashing to prevent water penetrating behind the lean-to

Next up, we had a damp patch appear in our living room about halfway along an external wall. What was strange though was that it was on a wall where we had a glass lean-to canopy installed and the damp was appearing about 6 inches below the roof of the canopy!

The canopy was bolted to our wall with silicone running along the length. However, upon investigation, it was clear the silicone was failing and water was penetrating behind it, running down to the wall bolts.

The wall bolts were giving the water an easy route into the brickwork and from there, it was entering our living room and causing our damp patch.

The solution? Have a builder install lead flashing along the length of the canopy to guarantee no more water can penetrate behind it.

Another problem solved!

Problem #3: Leaky Roof

Just as we were starting to relax, another damp patch appeared! This time it was in our spare bedroom, which also has a chimney breast.

The damp was appearing on the ceiling at the top of the chimney breast. Cue more investigation!

This time we found that as well as the chimney needing repointing, there was also a gap where the lead flashing around the chimney had failed. Plus, several of our ridge tiles had come loose and the mortar had crumbled away.

Repaired chimney & ridge tiles
Our newly repaired chimney, flashing, and ridge tiles.

This time a roofer was called and the problems were quickly patched up with more lead flashing and some new ridge tiles added.

Another problem solved!

Problem #4: Crumbling Brickwork

Our fourth (and hopefully, last!) experience of penetrating damp came where we least expected it – on the more modern cavity wall extension.

With several blown bricks on the corners of the extension suggesting there’s a long-standing issue, we noticed the damp on the wall was only getting worse.

The cause has proven difficult to pinpoint. One possible issue is the guttering ran just short of the end of the roof which won’t be helping. Another possible cause was old cracking silicone around the windows and doors.

Blown brickwork on corners of extension
The brickwork has deterioated on the corners of our extension

We had both fixed and are now waiting to see if the problem is resolved. If not, our conclusion is that, as the bricks are porous, water is penetrating them and then is unable to escape due to the fact the walls are painted white.

In this case, we’ll get the wall rendered with a waterproof and breathable silicone render.

The final problem is pending resolution but we’re confident we’ll get to the bottom of it.

All in all, our experience has shown that water will find even the smallest of gaps and, if left untreated, will go on to cause bigger problems both inside and outside your home.

Is penetrating damp the same as rising damp?

It’s important to appreciate that penetrating damp is different from rising damp – a damp problem that tends to be found on ground floor walls. Rising damp is caused by moisture rising from the ground through capillary action – that’s the movement of water in a porous material’s space.

Penetrating damp can appear as isolated damp patches that can increase in size after rain, whereas rising damp usually forms a horizontal band of dampness along the base of the wall.

This type of damp is also different from condensation, which is caused by excess moisture in the air due to poor ventilation or heating.

Condensation usually forms on cold surfaces such as windows or walls and can lead to mould growth.

Damp causing mould in room corner
Damp has caused mould growth in the corners of our living room!

The most noticeable sign of penetrating damp will be damp patches appearing on the inside of exterior walls, particularly around windows and doors.

These damp patches may darken when it rains and lighten as they dry out.

In severe cases, penetrating damp can lead to structural damage within the building.

While penetrating damp has been our main issue, we’ve also experienced rising damp, especially in the corners of our rooms.

Will penetrating damp affect my health and home?

Penetrating damp can cause various problems for your home and your health.

It can damage the structure and fabric of the property, such as plaster, paintwork, wallpaper, skirting boards and floor timbers.

It can also cause wet rot or dry rot to develop in timber elements, which can weaken the structural integrity of the building.

And it can create an unhealthy environment for you and your family since it can increase the risk of respiratory problems, allergies and asthma due to mould spores and bacteria.

In fact a 2001 study found that “dampness in buildings appears to increase the risk for health effects in the airways, such as cough, wheeze and asthma.“.

Further, it went on to conclude that “There also seems to be an association between “dampness” and other symptoms such as tiredness, headache and airways infections.”.

The study went on to conclude that “the evidence for a causal association between “dampness” and health effects is strong”.

Therefore, it’s clear that dampness in your home is not something you should accept and it’s important to deal with the problem ASAP, both for your and your property’s health!

How do I spot penetrating damp?

Penetrating damp is fairly easy to spot, either through damaged plaster, rotten wood or mould growth, etc...

To spot penetrating damp, you should look out for the following signs:

  • Damaged internal decoration: the deterioration and staining of internal walls.
  • Damaged plaster: check for disintegration, ‘salting’ or blistering.
  • Floor timbers and/or skirting boards that have rotted: look for wet or dry rot that will lead to decay.
  • Local damps: check for any random damp patches that are either at a low or a high level and can sometimes grow in size.
  • Mould growth: easy to detect with a musty smell and spoilt decor.
  • Brick damage: always inspect external brickwork for cracks and spalling – that’s when brick or concrete crumbles.

How do I treat penetrating damp?

To treat penetrating damp, you should first locate and fix the source of the moisture. This may include:

  • Fix any damaged roof tiles;
  • Repairing mortar or plaster cracks;
  • Mending broken pipes;
  • Fixing faulty guttering or roofing;
  • Repointing brickwork.

We mentioned earlier that bricks are porous so you could use cladding, external render or weatherproof paints for this purpose. Be aware that these solutions will alter the appearance of the masonry.

Furthermore, this work should be carried out by a qualified builder or plumber.

Should a building defect be to blame for a penetrating damp issue, then the problem will need repairing first before treatment to deal with the damp can begin. Not doing so will see the problem recurring.

Once the source of moisture is determined, you should then dry out the affected area and remove any damaged materials such as plaster or timber.  You may need to use a dehumidifier or a fan to speed up the drying process.

This step may require professional help, particularly for larger areas or if the damp has led to structural damage.

You should also treat any mould or rot issues with appropriate fungicidal products and replace any affected materials with new ones.

How I stop penetrating damp recurring?

To prevent penetrating damp from happening again, you should apply a water-repellent fluid to the external wall of your property.

This will create a protective barrier that will prevent water from seeping through the wall.

You should also maintain your property regularly and check for any signs of damage or deterioration that could allow water to penetrate.

In some cases, secondary protection measures may be necessary. This could include:

  • Applying a damp-resistant plaster to prevent future moisture penetration.
  • Using specific treatments to combat mould and mildew growth.

Why good ventilation is important when dealing with damp

Good ventilation is crucial to avoid the creating of damp at home.

There’s also another issue when it comes to dealing with penetrating damp in a home and that’s ensuring good ventilation.

Proper ventilation is a crucial aspect of maintaining a healthy and comfortable living environment in your home.

This is the process of exchanging indoor air with fresh outdoor air, allowing the removal of pollutants, excess moisture and odours.

One of the notable indicators of penetrating damp is that you will smell the damp problem before you see it, depending on where it is.

So, when it comes to preventing and managing dampness issues, such as penetrating damp, adequate ventilation plays a significant role. Here’s why:

Moisture control

Proper ventilation helps control moisture levels in your home. Moisture can accumulate from various sources, including cooking, bathing, drying clothes indoors and even breathing. If this moisture is not effectively removed, it can lead to condensation, which promotes the growth of mould and mildew.

Prevention of condensation

Our review of Wallrock KV600
We installed thermal lining paper in one room to prevent condensation.

Condensation occurs when warm, moist air comes into contact with cold surfaces, leading to the formation of water droplets. It often appears on windows, walls, and other areas with poor insulation or inadequate airflow.

Continuous condensation can result in damp patches, peeling wallpaper, and even damage to structural components.

We’ve tried several methods to reduce condensation (and the mould it causes) in several of our rooms, each to good effect. Our favourite method is to use thermal lining paper (check out our Wallrock thermal liner review) but we’ve also had good effect with anti-condensation paint, too.

Odour control

Inadequate ventilation can result in stagnant air, which can lead to unpleasant odours lingering in your home. Whether it’s from damp, cooking smells, pet odours or anything else, proper ventilation helps to eliminate these unpleasant scents and refresh the air inside your home.

Improved comfort

Good ventilation helps create a more comfortable living environment. It allows for the regulation of temperature and humidity levels, preventing stuffiness or excessive dryness.

Tips for achieving proper ventilation:

Here are some quick Property Road tips on how you can achieve proper ventilation – especially when dealing with penetrating damp issues.

Natural ventilation

Make use of windows and doors to allow fresh air to enter and circulate throughout your home. Open windows on opposite sides of a room to encourage cross ventilation and maximise airflow.

Mechanical ventilation

Install extractor fans in areas prone to moisture, such as kitchens and bathrooms, to remove humid air directly at the source.

Consider investing in whole-house ventilation systems, such as mechanical ventilation with heat recovery (MVHR), to provide consistent and controlled air exchange throughout your property.

To try and reduce moisture levels in our home, we opted for a Positive Pressure Ventilation (PPV) system. It was relatively cheap to install (we paid a few hundred pounds) and it’s easy to maintain.

Positive Pressure Ventilation System
The PPV system we installed in our smallest bedroom

It’s very non-intrusive, all you end up with is a small vent in the ceiling of an upstairs room or landing. Ours was installed in our smallest bedroom and it gently pumps in filtered air from the roof space throughout the day.

While it does mean the heating has to work slightly harder in winter, we’ve found the increase in our energy bills to be very small, but our in-home humidty levels are much improved.

Typically, we’ve gone from humidity levels of 70-80% down to a much healthier 50-60%. We’ve also noticed much less condensation on our windows in a morning too.

Of course, we needed to stop the causes of our penetrating damp first, but once we had done that, adding a PPV system was the logical next step to improve the air quality of our home.

How common is penetrating damp?

Penetrating damp is a common problem in the UK that can cause serious damage to your home and your health if left untreated.

It’s worth noting that old buildings tend to be more susceptible to penetrating damp due to their solid wall construction and lack of modern damp proofing measures. Therefore, extra care should be taken when maintaining and repairing older properties.

What is penetrating damp?

Penetrating damp is a prevalent issue that can cause significant damage if left untreated.

However, with the right knowledge and approach, it’s entirely manageable.

Remember, the key to effectively treating penetrating damp lies in correctly identifying the cause and taking appropriate action to not just treating the damp but also to prevent its recurrence.

If you suspect your home has a problem with penetrating damp, it’s always advisable to consult a professional who can provide expert advice and treatment options.


  • Steve Lumley

    Steve Lumley has years of experience writing about property. His output has covered everything from property investment, news for landlords and student tenants to articles on how to run a successful portfolio and starting out as a property investor. He has also written several books on the subject.

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  • Paul James

    Paul James, is a marketing expert with a passion for property. As well as being a property investor, Paul has also worked within the marketing departments of some of the UK’s leading estate agents. Paul is the founder of Property Road.

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