What Is Damp Proofing Guide

What Is A Damp Proof Course?

Dampness in buildings has been problem which builders have sought to overcome for hundreds of years, often by installing a damp proof course. A wall built off the earth with no damp proof course will almost certainly become damp over time as water travels up the wall from the ground. 

So in modern terms when we consider what is a damp proof course we are looking at a variety of materials, installed at the base of a wall designed  to stop water rising up a wall. 

plastic damp proof course visible no rising damp exeter plymouth torbay south hams exmouth

A damp proof course (often abbreviated to DPC) is a barrier installed in a wall to prevent water rising by capillary action through a phenomenon known as rising damp. Rising damp is when water rises from the ground into property through the walls or floor. The damp proof course may be horizontal or vertical. During construction a damp proof course is usually laid below all brick and stone walls and solid floors. The picture above shows a fairly typical modern plastic damp proof course in a brick wall. 

What Is Damp Proofing?

Damp proofing is a general term that covers the methods and materials used to prevent damp from affecting a building. 

This could include installing a new damp proof course, external weatherproofing or tanking depending on if the damp is rising, penetrating and where it is coming from. There a many methods of damp proofing depending on the situation, book a survey with a Damp Genius to find out which suits your property. 

Types Of Damp Proof Course

Most properties in Devon, Somerset and Dorset should have a damp-proof course visible at a minimum of 150 mm above ground level. This may appear as a mortar course with a bitumen or plastic damp proof course sheet sticking out slightly.  Damp proof courses are required in all new build properties in order to prevent rising damp from occurring.

You can check your own property for a damp proof course by looking at the mortar, between bricks or stones, approximately 150mm or 6″ above the external ground. Looking from the outside is best but if the building is rendered you may not be able to see it. A good little trick is to look in the house under the stairs or in an electrical cupboard as sometimes these areas have not been plastered. 


slate damp proof course devon somerset torbay

Installation of a damp proof course was made compulsory in 1875 however ones from around this time were usually installed badly and no longer work. Slate was typically used as it is dense enough to build a wall directly off. Unfortunately over time building movement or freezing and thawing can cause these slate damp proof courses to break apart. 


plastic damp proof course visible no rising damp exeter plymouth torbay south hams exmouth

Buildings constructed from about 1920 onwards moved to having bitumen felt damp proof courses installed. More modern homes built this century have plastic damp proof courses installed. These are far more resilient than the older slate types, however, they can and do still fail. The bitumen type are common damp proof courses in Exeter terraced houses.

Remedial Injected

remedial damp proof course injection devon
source: safeguard europe

When an existing damp proof course fails the best option for treatment is often to inject a siliconate damp proof course. Unlike other types of damp proof course this does not create a physical barrier and instead lines the pores in the mortar with a slippery material so that water cannot be pulled up them through capillary action. 

Typical Damp Proof Course Detail

The damp proof course detail drawing below shows a damp proof course in a brick cavity wall with a solid floor internally. Note that the damp proofing is installed 150mm above the external ground level and so the section of internal floor and wall below this level must have damp proofing applied internally.

source: surveyorsnearme.com

The damp proofing detail below shows a damp proof course installed in a solid brick wall with a suspended timber floor. Note that the damp proofing barriers is installed below the timber floor to prevent moisture damaging the wood. 

What Happens If A Damp Proof Course Fails?

Now that you know what is a damp proof course it is time to look at the consequences of one failing. There are a number of problems which can occur such as:

  • Excess moisture in the air creating a damp, unpleasant, unhealthy living environment.
  • Paint and decoration flaking off the wall.
  • Plaster degrading and literally falling off the wall in chunks. 
  • The property can be very difficult to sell.
  • Mortgage providers are often reluctant to lend on a damp property. 
  • Timber floors can become damp putting it at risk of a Dry Rot outbreak. 
rising damp in a wall rising damp exeter torquay plymouth exmouth

Damp Proofing Specialist

Ensuring that your property in Devon, Somerset or Dorset has adequate damp proofing can be complex with many factors to consider. It is vitally important that your damp proofing specialist understands what is causing the damp (rising damp, penetrating damp, leaks, high ground levels etc) before specifying any remedial damp proofing. 

Damp Genius are experts in damp proofing and work with industry leading product suppliers to offer the best solutions tailored for specific properties. Our damp proofing specialists can show you what is the damp proof course type already in place, if it has failed, and the the best form of damp proofing to fix the problem. 

Contact us today to book a survey or get some advice. 

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If you need a solution to a damp problem or require a specialist survey then get in touch using this form. We are very friendly and happy to help. 

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