prevent penetrating damp

Penetrating damp

A Guide to Penetrating Damp

Due to the high amount of rainfall that we get here in the UK, penetrating damp is a common problem in UK homes, especially when it comes to older buildings that may not have been built with damp-proofing in mind. Penetrating damp is caused when moisture gets into the building through the external walls, where it can lead to serious problems in the property like mould and even structural problems if it is left unchecked over time. Whether you own a home and have noticed damp problems that you think might be caused by penetrating damp, or are looking into buying a new home and want to make sure that you are not going to be at risk of dealing with serious damp issues in the future, it’s important to understand what penetrating damp is, how you can avoid it, and how to repair it if it happens in your house.

What Causes Penetrating Damp?

Penetrating damp is a type of damp that occurs when the moisture from outdoors is able to make its way into the property. This can be through various different ways including when bricks are not correctly sealed to repel moisture, if there is no cavity wall in a property, or leaks that come in through cracks and holes in the bricks, roof, or around window frames and doorframes. Penetrating damp is more often than not the result of a property that has not been properly maintained.

What are the Main Penetrating Damp Signs?

It is not always easy to immediately identify damp patches as penetrating damp, since they can often look similar to condensation damp or even rising damp depending on where the patches are located in the home. However, damp that affects both the interior and the exterior of the property tends to be one of the biggest signs that you are dealing with penetrating damp. Some other signs of penetrating damp to look out for in your home include:

  • Damage to décor: If you have noticed discoloured, damp, flaking or peeling wallpaper or paint in the home, penetrating damp could be the cause.
  • Damaged plaster: Plaster that has been affected by penetrating damp will show signs of wear and tear, even if the plaster is fairly new. This is because the excess moisture will damage the quality of the plaster.
  • Localised damp patches: Penetrating damp will typically lead to patches of localised damp in the areas where the moisture is able to penetrate through into your home. No matter how many damp proofing methods you use, these patches are unlikely to stay dry and will usually reoccur quickly.
  • Mould growth: Mould spores thrive in a damp environment. While mould is often a sign of condensation, it can also indicate penetrating damp.
  • Wet rot: Any wooden floors or walls that are affected by penetrating damp might show signs of wood rotting, which can be problematic for the structure of the building if left unchecked.

However, bear in mind that it’s not just the inside of your property that can be affected. Outside your home, look out for the following:

  • Damage to brickwork: External brickwork that appears damaged is a sign of penetrating damp. The damage is often caused by the moisture freezing and expanding in cold conditions which leads to cracks within the bricks.
  • Moss: Moss and algae will grow on the exterior walls of your home when they have access to high moisture levels here. If the problem is not repaired quickly, the moss and algae will spread and cause the brickwork to deteriorate over time.

Penetrating Damp on Internal Wall – Which Areas are at Risk?

While penetrating damp can impact any wall in your home that has an external side, there are some types of property and areas of the house that tend to be at a higher risk of suffering from this type of damp. Houses that were built with solid walls rather than a cavity wall are more likely to have penetrating damp problems since the cavity wall offers an additional layer of protection against the moisture getting inside the building, especially when it is filled with insulation. However, having cavity walls at your home does not automatically mean that you are not going to experience penetrating damp problems. In some cases, issues with the cavity wall insulation can allow the water to reach the inner wall due to the wall becoming blocked, when there should usually be a gap of air that prevents this.

Penetrating Damp on the Chimney Breast

Penetrating damp on your chimney breast is most usually caused by issues with the chimney stack. If you do not use your chimney in your home, one way to ensure that you don’t have to deal with this problem is to have the chimney breast and stack removed, which can also free up space in your property. Open-topped chimney pots that are not in use are a common cause of penetrating damp on the chimney breast since they may allow moisture to enter through and travel to the base of the chimney stack. One main sign of this is that the damp is around the base of the chimney breast since the moisture is travelling up from the inside. If there is damp around your chimney breast that at first glance appears to be rising damp or a problem with your damp-proof course, bear in mind that it could actually be penetrating damp.

Cracks or splits in the mortar around your chimney stack or at the base of each chimney pot can also lead to damp problems with your chimney breast. If you can see cracks located here, there’s a high chance that water from rain or moisture is entering through them and running down the inside of the chimney stack, leading to damp problems. This problem might occur in the form of staining on your chimney breast or damp walls at either side of the chimney breast.

What Causes Penetrating Damp Around Windows?

Penetrating damp around your windows is usually a problem with the window frame – typically, it is not property sealed or in the case of an old window, the sealant is no longer effective. In this case, you may be able to have the windows resealed to correct the problem and prevent future moisture from getting through. However, in severe cases, it might be necessary to completely replace the window. If the damp that has been caused by the moisture getting through a faulty window frame has caused serious damage to the internal or external walls, this may require you to have the affected parts of the wall replaced or replastered once the source of the damp has been dealt with.

Can You Get Paint to Stop Penetrating Damp?

You may be able to apply a paint or treatment to your external walls to prevent moisture from getting inside the bricks. However, it’s important to bear in mind that these treatments are only effective when the cause of the penetrating damp is porous brickwork, and will not usually be effective against other causes of penetrating damp such as cracks in the brickwork or roof or windows that need to be resealed. You should treat the outside of your house using the damp-proof sealant or paint on a dry day. The treatment is not designed to last forever and you will usually need to redo it around once per year in order to continue experiencing the benefits.

Inside your home, you can also get damp-proofing paint to stop damp patches from reoccurring and in some cases, reinforce the walls. However, once again, these paints are unlikely to work if the root cause of the issue has not been dealt with. Applying damp-proof paints and other treatments on both sides of the wall is likely to work when the damp is caused by moisture getting in through the bricks; however, any cracks in the walls or problems with your chimney pots are going to continue letting moisture in no matter how great a damp-proofing product you use. This is why it’s important to contact a specialist who can help you determine why you are experiencing penetrating damp in your property and fix the root problem before damp-proofing your home. Continuous and regular maintenance of your property, particularly the external walls, roof and window frames, is essential to prevent penetrating damp from reoccurring in the future.

Penetrating damp occurs when moisture from the outside makes its way to the inside of the home and can be a common problem in UK properties due to the high amount of rain that this country gets. Penetrating damp can impact both the internal and external walls along with any woodwork in a home, which is why it’s so important to have this issue dealt with as quickly as possible to avoid structural damage. Thankfully, once the root of the issue has been dealt with, keeping up with good maintenance on your home is usually an effective way to avoid penetrating damp coming back.


Return to main independent damp surveyors page.

Comments for this post are closed.