Damp proofing during property extensions

When it comes to property extension, one of the crucial factors that needs to be considered is damp proofing. Damp proofing is the process of protecting a building from moisture, which can cause structural damage and health problems due to mold growth. In this article, we will explore the essential damp proofing considerations and techniques when extending your property.

Understanding Damp and Its Causes

Damp is a common problem in many properties and can affect both old and new buildings. Moisture can seep through walls, floors, and ceilings and cause several problems, such as:

  • Structural damage
  • Health problems due to mold growth
  • Electrical hazards
  • Aesthetic issues such as peeling paint and wallpaper

The causes of damp can vary, but some of the most common include:

  • Rising damp caused by moisture seeping through the ground and up through the walls
  • Penetrating damp caused by water seeping through walls or roofs
  • Condensation caused by insufficient ventilation and poor heating

Before extending your property, it is essential to identify the type of damp problem you are dealing with, as this will help you choose the right damp proofing technique.

Damp Proofing Techniques

There are several damp proofing techniques that you can use to protect your property from moisture. Some of the most common ones include:

Chemical Damp Proof Course (DPC)

A chemical DPC is a layer of waterproof material that is inserted into the walls to prevent rising damp. This technique is suitable for properties that are already built and cannot have a physical DPC installed. The process involves drilling holes into the walls and injecting a waterproof resin that lines the walls and creates a barrier against moisture.

Physical Damp Proof Course (DPC)

A physical DPC is a layer of waterproof material that is installed within a building to protect it from moisture. This technique is suitable for new builds or properties that are undergoing significant refurbishment. The process involves installing a waterproof barrier between the floor and the wall, which prevents moisture from seeping through the walls.


Tanking is a damp proofing technique that involves creating a waterproof barrier within the structure of a property. This technique is suitable for properties that are located in areas prone to flooding or extreme weather conditions. The process involves applying a waterproof coating to the walls and floors.

Cavity Wall Insulation

Cavity wall insulation is a technique that involves filling the space between the inner and outer walls with insulation material. This technique helps to prevent heat loss from the property and can also provide a barrier against moisture.

Damp Proofing Considerations When Extending Your Property

When planning an extension, it is essential to consider damp proofing as part of the design and construction process. Some key considerations include:

Site Survey

Before starting any construction work, it is crucial to carry out a site survey to identify any existing damp problems and potential sources of moisture. This survey can also help to determine the type of damp proofing technique that is suitable for the property.


Good drainage is essential to keep water away from the property. When extending your property, it is essential to consider the drainage system and ensure that it is functioning correctly and has the capacity to handle the increased water flow.


Proper ventilation is essential to reduce humidity levels within the property and prevent condensation from forming. When extending your property, it is essential to consider the ventilation system and ensure that it is adequate to meet the increased demand.


The type of flooring used in an extension can also affect the damp proofing. For example, porous materials such as wood and carpet can absorb moisture and cause mold growth if not properly protected. When extending your property, it is essential to choose a non-porous flooring material or to install a damp proof membrane under the flooring.


Good insulation is essential to prevent heat loss from the property and can also act as a barrier against moisture. When extending your property, it is essential to consider the insulation requirements and ensure that they meet the building regulations.


  1. How can I tell if my property has a damp problem?
  2. Some common signs of damp problems include peeling paint, wallpaper, and plaster, a musty smell, and visible mold growth on walls and ceilings.
  3. What is the best damp proofing technique for my property?
  4. The best damp proofing technique for your property will depend on several factors, including the location, age, and type of property, and the type of damp problem you are dealing with.
  5. Can I damp proof my property by myself?
  6. Damp proofing requires specialized knowledge and equipment and is best left to professionals with experience in the field.


Damp proofing is a crucial consideration when extending your property. Proper damp proofing techniques can protect your property from moisture and prevent structural damage, health problems, and aesthetic issues such as mold growth. It is essential to consider sites, drainage, ventilation, flooring, insulation requirements, and consult professionals while extending your property to ensure effective damp proofing.

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