What causes penetrating damp

What causes Penetrating Damp? Signs & Treatment

Did you know that there are different types of damp? Rising damp, penetrating damp, and condensation are the common types of damp that occur in UK homes. Here in this article, we will discuss what causes penetrating damp.

What does Penetrating Damp look like?

Also referred to as lateral damp, penetrating damp occurs when the water passes unhindered through porous stonework and bricks from the outside of your building and into the property. It can happen at any level within the building, including walls, ceilings, and roofs. 

Penetrating damp is a common problem found in old properties with solid walls. Older buildings that have poor maintenance are at higher risk of experiencing damp. Modern buildings have more protection from lateral damp due to the usage of cavity walls. However, a modern building may also suffer from penetrating dampness where there is defective artistry or designing error. 

Like other damp, if left untreated for an extended period, it can cause structural issues and considerable damage to your property. In addition, it can also cause fabric deterioration, including damaging the walls, ceilings, floors and causing the timber to rot. 

What does penetrating damp look like? It can affect entire wall areas or form patches. It can get worse after a heavy downpour. So your home or commercial building in the UK is at risk of rainwater penetration. Penetrating damp commonly affects the areas exposed to extreme weather conditions or there is a structural defect in the property.

damp proofing specialist applying paint

What Causes Penetrating Damp?

Lateral damp commonly occurs if you live or own a building with structural defects, defective roof coverings, or faulty pointing to windows and doors. Defective masonry is also a significant cause of penetrating damp. 

Building Defects 

Inadequate drip grooves, damaged roofs, leaking downpipes and gutters, defective seals around doors and windows, and other building defects are the main culprits causing penetrating damp. If you find any defect in your property, it should be fixed immediately because they are a continuous source of dampness that can ruin your interiors. 

Damaged Brickwork

Faulty pointing and spalled bricks can also be the reason behind penetrating damp. Damaged brickwork is not able to fully withstand rain penetration. Also, it further causes damage to the masonry by deteriorating structural instability. When mortar and spalled brick joints can be seen, the masonry should be checked to determine the extent of damage caused by penetrating damp. The damaged joints can be waterproofed and repaired against additional damage with repointing additives. 

Porous Bricks

Another cause of penetrating damp is porous bricks. Water permeates through the pores and penetrates masonry. Whenever it rains, the water seeps through the brickwork. It causes isolated damp patches on internal walls that increase in size during heavy rains. Water repellent creams and chemical agents are the best for treating penetrating damp. 

penetrating damp on the exterior brickwork

Bridging the DPC causes penetrating damp

In addition to the points mentioned above, brickwork, render, and pointing can deteriorate with frost, physical damage, or age. When the older buildings are affected by penetrating damp, they can deteriorate over time or be storm-damaged. If the building structure fails, your property enables the moisture to soak entirely across the wall. It shows that the waterproofing system of your property is failing. 

Penetrating damp is found where the external ground levels are higher than the damp-proof membranes or internal floors to concrete floors. Moreover, the damp can also be found in the areas such as the cellars or basement of your building which are below ground level. 

Proper diagnoses of the damp issue are significant to specify an appropriate remedy. 

Signs of Penetrating Damp

Like every other damp, penetrating damp is unsightly and leads to expensive structural timber rot repairs. If you know the symptoms of penetrating damp, you can deal with them as soon as possible. Here are some of the common symptoms of penetrating damp:

  • Damp irregularly shaped patches
  • Damaged plaster
  • Black mould growth
  • Leaky roof
  • Damaged timber
  • Musty smell

The localised damp patches on random locations won’t dry out, even if you many techniques to dry them. Besides, these damp patches or watermarks on the walls get more prominent after the heavy downpour. Another sign of penetrating damp is salting. It is the process in which the water brings the natural salts of the wall to the surface and result in a puffy residue found on your decoration or plaster. 

damp patches on walls

Areas Affected by Penetrating Damp

The places where you are more likely to find penetrating damp include:

External Walls

Missing mortar pieces or cracks in masonry can cause penetrating damp. If this is the situation, then ensure that these are repaired with a suitable filling material. The external render or masonry become porous or crack breaking the render from the masonry enabling rainwater to enter. 


Roof ridge tiles, the pointing, missing tiles, and the joint where the roof meets chimney or wall are the main areas to check for penetrating damp. If you find any loose or missing, you need maintenance to prevent or stop penetrating damp. 

Door Frames

Cracks that might exist around door frames require repair. Apart from this, if the external door of your building lacks a weather bar which is a board at the bottom that protects from excessive rain, then it is time you get one installed. 

Window Frames

You must inspect window frames to see if they have any cracks or gaps. If they exist, then they must be filled with a frame sealant. Besides, ensure to check that a groove is installed under the window sill that is needed to stop the water. If it exists, ensure that it is filled in with a hardwood strip. 

External Downpipes, Gutters, and Drains

You must check the external rainwater goods whether they are leaking or not. You must inspect drains to make sure they are not clogged, causing water to enter the building. 

How to treat Penetrating Damp?

Before you look for the options, you need to diagnose the causes behind the damp properly. Then, you should consult a penetrating damp expert who can survey your property and advise you to eliminate the damp issues. 

Commonly, traditional building techniques are used along with repair systems and new products to dry out your building. In addition, you can apply a chemical water repellent or physical membrane to stop the problem from returning if it is appropriate. 

In severe cases of penetrating damp where the mortar and stonework become too porous that the damp is soaked through the external walls into the property, you can use a special cavity membrane fitted to the outside of the external walls with a typical render. The membrane system waterproofs the exterior of the building. 

Once the damp is diagnosed, it takes some time for the fabric to dry out, depending on the drying technique being used. 

Advanced damp on high ladder using spray injection to treat penetrating damp wall

Role of Cavity Wall Insulation 

Cavity wall insulation is quite popular as it enhances the heat retention of the building. It is common in UK houses. The cavity wall construction includes an inner wall built to surround the interior of the building and an outer wall covered with pebbledash, paint, or render. There is a gap left in the cavity between two walls to protect the interior walls from damp. 

Contact us for penetrating damp treatment

If your property is experiencing penetrating damp, call our damp specialists to book a survey

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