Lateral damp is when groundwater penetrates sideways into a property through cracks or porous building materials. Lateral penetrating damp enters walls horizontally from the side, typically below the damp proof course (DPC) level, leading to water damage.
It can affect any floor which is in contact with soil, but is most common in basements.
Areas that have high water level – such as Fulham, Putney and Richmond – are more vulnerable to lateral damp.
You can learn more on the causes of lateral damp in our article.
Definition and Causes
Lateral damp is a type of dampness that occurs when groundwater penetrates sideways into a property, affecting any floor in contact with soil. This type of dampness can erode building materials and make a room uninhabitable due to excessive moisture. Lateral damp is often linked to rising damp, which is caused by water traveling upwards through porous building materials. Both types of damp can occur simultaneously, so solving one does not necessarily mean the property is damp-free.
The causes of lateral damp include soil pressing against a cracked or porous wall, allowing groundwater to seep through and saturate the wall. Soil becomes wetter the lower you dig down, increasing the risk of lateral damp for deep cellars and basements. Buildings on sloped ground are more vulnerable to lateral damp due to the slow flow of groundwater downhill. Soil can rise over time, exposing groundwater to walls not originally built to withstand lateral damp. In such cases, excavating excess soil buildup can help prevent the problem from recurring.
Comparison to Rising Damp
Unlike rising damp, which is caused by water traveling upwards through porous building materials, lateral damp enters the wall below the damp proof course, attacking the lower levels laterally (from the side). Lateral penetrating damp is a specific problem in homes, often misdiagnosed as rising damp or normal penetrating damp. It typically affects lower floors, especially in homes with cellars or basements. Lateral penetrating damp occurs when the ground level is higher than the damp proof course, allowing water to enter the walls below the current level of protection.
HOW TO SPOT LATERAL DAMP AND CHECK DAMP PROOF COURSE
Look out for paint that’s peeling or has a bubbly appearance, or plaster that’s discoloured and/or crumbling.
Damp patches, which are visible signs of moisture on walls, can also indicate rising and lateral damp. Walls affected by lateral damp are also likely to be cold and wet to the touch, and if hygroscopic salts are present, then you may see a white, chalky coating as well.
Black, sooty mould is a dead giveaway of a damp problem and can be just as easily smelled as spotted.
Diagnosis and Treatment
To spot lateral damp, look for paint that’s peeling or has a bubbly appearance, indicating lateral damp. Discolored and crumbling plaster can also be a sign of lateral damp. Walls affected by lateral damp are likely to be cold and wet to the touch. A white, chalky coating may be present if hygroscopic salts are present. Black, sooty mold is a clear indication of a damp problem and can be easily smelled.
To treat lateral damp, a bespoke approach using a Structural Water Proofing (tanking) system is required. The system involves stripping the plaster back to the bare wall and installing the tanking system. Coats of a cementitious slurry and bonding agent are used to waterproof the wall. This system is perfect for damp-proofing a basement or just one wall. It is a different approach from rising damp or normal penetrating damp, requiring a specific solution.
In addition to treating the damp, it’s essential to address the underlying causes of the problem. This may involve excavating excess soil buildup, repairing cracks in the wall, or replacing missing roof tiles. Using a high-quality silicone sealant can also help to prevent water from entering the wall. By understanding the definition and causes of lateral damp, comparing it to rising damp, and diagnosing and treating the problem effectively, you can ensure that your property remains safe, dry, and free from damp-related issues.
LATERAL DAMP AND RISING DAMP CAUSE MOULD AND PROPERTY DAMAGE
If untreated, lateral damp can ruin paint and plaster, spread mould and cause electrical failures and shocks – none of which you want in a basement you intend to spend time in. Wet decking adjoining wall joints can contribute to lateral damp by allowing moisture to penetrate from the side.
Lateral damp causes more problems than just an unpleasant basement, it can also lead to severe structural issues for walls which the entire building is relying on for support. Wet soil can contribute to lateral damp by allowing moisture to penetrate walls from the side, especially in homes with basements or those built on sloping ground.
To prevent damage from lateral damp, building regulations require that all new builds with basements and all basement extensions are equipped with tanking systems. Wet soil resting against walls, particularly in basements or cellars, can lead to lateral damp by allowing moisture to enter the structure from the side, below the damp proof course.
You can learn more about treating lateral damp in our article.
