Penetrating damp – What is it and how can you fix it

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penetrating damp

In this article we will be looking at penetrating damp. We will be explaining what penetrating damp is. As well as some of the common causes and how they can be fixed.

This will include DIY damp proofing solutions, as well as some jobs that will require you to hire a professional.

So, what is penetrating damp?

Penetrating damp is caused when water enters a property from the outside. This is usually caused by defects in the outside wall, such as damaged brickwork and pointing. Because of the way it enters the property, it usually appears as damp patches on inside walls. These patches will usually be concentrated around the area of the defect and may become darker and wetter when it rains.

How to identify penetrating damp

Penetrating damp is quite easy to identify because of the way it appears in your property. It will usually be isolated in one area; these damp patches will quite often flare up and down depending on the weather.

Usually you can rule out other forms of damp, such as condensation or rising damp, because the symptoms are slightly different.

For example, you will be able to rule out rising damp if the damp patches don’t start low down at skirting board level.

With condensation you will usually find that it is more spread out, rather than patches of penetrating damp. You are also unlikely to notice it until things like black mould begin to form. This is because it does not usually saturate the wall as much as water that is penetrating one concentrated area.

One area where there can be confusion with penetrating damp and condensation is around windows. A window acts as a dew point, and this means that condensation is naturally attracted to them. Due to this you will often find areas of damp and mould around windows.

However, windows are also an area where penetrating damp is quite common. Over time windows can form defects that allow water to penetrate in, these include:

  • Damage and wear to sealant around the window
  • Window trims can become damaged
  • Sills can be broken or damaged

All of these will potentially allow water to penetrate in. This could result in a similar effect to condensation. However, you can usually just go outside and spot these defects quite easily. Also, if your window glass is regularly covered in condensation on the inside, this is a clear sign you need to fix condensation issues.

Common causes of penetrating damp

There are several causes of penetrating damp. In this section, we will be looking at some of the most common. This should provide you with a checklist that you can run through, to help identify penetrating damp.

Cracked bricks

This is usually going to be quite easy to spot. Go outside and look at the outside wall for damage to existing brickwork. This could be at the exact point you see the damp coming inside, or possibly further up the wall.

Damaged pointing

When you are checking your brickwork for any damage, you should also check the pointing. Good pointing will usually last for 50+ years. However, it does deteriorate over time and will eventually need replacing.

Once the pointing wears down or falls out, it forms a very easy path for moisture to enter your property.

Old damaged render

Is your property rendered or pebble dashed? If it is and there is visible damage, this may be the cause of your penetrating damp. Even small cracks in your render can allow water to get in and build up behind the render. Following this it can soak into your brickwork and mortar joints.

Old flaking external masonry paint

This is very similar to the problem with render or pebble dash. Once an opening exists it allows water to enter and build up under the surface. Overtime it is highly likely that this will result in penetrating damp

Old porous bricks

All bricks are porous to a certain extent. However, older brickwork tends to be more porous than modern bricks. This means that they can absorb excess moisture. Overtime this can cause penetrating damp.

This is less obvious than a visible defect, so if this is your last option you may need to call in a professional, to identify this issue for you.

Damaged guttering and down pipes

Damage to guttering and down pipes is a very common problem. It will allow water to continuously run onto the walls. This can combine with other defects and allow a lot of water to enter your property.

Ideally any issues with your guttering or downpipes should be fixed as soon as they are spotted

Roof defects

Another common way for water entering your property is via the roof. This could be caused by a variety of problems, such as slipped or cracked tiles, pointing, flashing etc.

You may be able to spot defects from the ground or using a ladder. However, it is advised to get help from a roofing professional

Water ingress around windows and doors

As we mentioned previously this is usually quite easy to identify. Check for damage to sealant, trims, and sills on the outside of the window. These are all potential ways for water to get in. The good news is once you spot them, they are quite easy to fix.

Cavity bridging

A bridged cavity is often formed by debris and other materials becoming clogged in the cavity wall. This causes a bridge that moisture can pass across.

When bridging is your issue, you are likely to also see other defects on this list. These will usually appear higher up the outside wall. Water will penetrate through the defect and run down the inside of the cavity. Once it reaches the bridge it will cross over and penetrate the internal cavity wall and enter your property.

You will usually need to hire a professional to identify and clear a bridged cavity. This will involve drilling a hole in the mortar between your brickwork. Following this they will insert a small camera to find the bridge. 

As you can see there are several different ways that penetrating damp can develop. Hopefully, the list above will give you a good starting point. Simply go through the list and see if you can find any of the problems we mentioned.

Ways to treat penetrating damp

Once you have identified the problem you can use some of the solutions below to fix your penetrating damp issue.

Replace or repair damaged brickwork

If you have identified damaged and cracked brickwork, the best way to fix this is to simply replace the brick. This may sound complicated, but if you are reasonably competent at DIY, you should be able to do this yourself.

The video below shows you exactly how this can be achieved with just a few of tools.

If this is something you are not confident with, or if it involves working at height, you could always hire a builder to do the work for you.

Repointing damaged mortar

Repointing is a very common way of solving penetrating damp issues. Depending on the size of the area, you may choose to do this yourself.

Re-pointing a couple of m2 should only take 1-2 hours and materials cost under £20. You can see another good video with step by step instructions below.

Repairing or replacing damaged render

If you have damage to existing render or pebble dash, then this will need fixing. The main problem here, is if the whole house needs re-rendering, this can be quite a big job. You can expect to pay anywhere from £20 – £70 per m2 depending on the type of render.

Smaller patching jobs should not be that expensive. But we would still recommend hiring a professional for this type of job.

Applying paints, creams, and water resistant treatments

One good way to waterproof your house is by adding an external waterproof barrier such as an external masonry paint or other waterproof treatment. This job can be done DIY, or you can hire a professional.

There are just a couple of things to remember here:

  1. If you are doing the entire house, this could require scaffolding. You will need to factor this into the cost. Hiring a scaffolding company can be expensive. An alternative here could be to hire something like a mobile tower scaffold.
  2. The second thing to consider, is this is a big job. Do you have the time to do the work yourself?

If you do hire a professional, they may charge by m2 or possibly a day rate. A standard day rate for this type of work would be anywhere from £120 – £200 per day. Most contractors will be able to give you a fixed price for the work. Just remember materials and scaffolding will be an extra cost.

Fix roof defects

There are lots of potential roof defects that can cause penetrating damp. Generally, we do not recommend carrying out this type of work DIY. For starters, it involves working at height, and secondly a good roofer will be able to fix small defects quite easily.

One important thing to remember here, is to get recommendations when hiring a roofer. Also get a few opinions. Do not just hire the first person that tells you, you need an entire new roof. This could be a very expensive way of fixing a very small defect.

Seal around windows and doors

This will usually involve adding or replacing old silicone sealant around the window or door. You may also need to replace or add trim in areas where it is damaged or lacking. Both are quite simple jobs that can be performed by anyone with a little DIY knowledge.

You can see a quick video below of someone adding sealant around a door and adding a small amount of trim.

DIY penetrating damp solutions

As you can see, there are lots of small defects that can cause penetrating damp. The vast majority of these can be fixed using a DIY method. In many cases it will be one small external issue that is causing the problem. When this is the case it is usually quite easy to fix with some basic tools and a small amount of spare time.

However, it is always recommended that you leave more complex or dangerous jobs to the professionals. Obviously, anything that involves working at height can be dangerous. Without the correct PPE and training accidents are a risk.

Also, anything that requires a high level of skill and a high quality finish, should probably be outsourced. If something like render is applied poorly, this could ruin the external finish of your property. Not only that, if it is applied incorrectly, it could cause more problems in the long term.  

Cost to fix penetrating damp

So how much does it cost to fix penetrating damp? Well, we have all heard the saying “how long is a piece of string?” and that saying is very appropriate here. The truth is it can be as little as £20 to do a small DIY repair. But for bigger, professional jobs you could be looking at thousands of pounds.

In many cases there will be individual defects that need fixing. This could be:

  • Replacing a brick
  • A small amount of repointing
  • A small fix to a section of guttering or down pipe
  • Adding some silicone around a window
  • A small amount of external painting or adding a cream or sealant.

All the above are low cost jobs. If you do them DIY, they will likely range between £20-£100 total. However, once you get to larger jobs, such as clearing cavity bridging or rendering an entire house, you will be looking at hundreds, or even thousands of pounds in expense.


So, what is penetrating damp? The answer to this lies in how the water is entering the property. It is essentially penetrating through surfaces such as your walls; this happens via defects in the building itself.

Due to this, Penetrating damp is one of the most common forms of damp. If you have already ruled out condensation, then it is highly likely that penetrating damp is your problem. All you must do now is find the cause and fix it.

Hopefully, the tips in this article have been helpful and I hope they help you get to the bottom of your damp problem.