Timberwise engineer injecting a damp proof course

What is a Damp Proof Course?

The most common form of protection from damp is the installation of a damp proof course into the walls of the building where the existing damp barrier has for whatever reason failed. In this guide, we will explain what a damp proof course is, how it works and why it is needed.

What Exactly Is a Damp Proof Course?

A damp proof course is a protective barrier against damp rising up the walls of the building. There are various types of damp proof courses that can be used but not usually in conjunction with each other.

If there is no existing damp proof course in place or an existing damp barrier has for whatever reason failed, then the building is vulnerable to rising damp problems.

Types of Damp Proof Courses

There are various types of damp proof courses that can be installed at your property, but the type that is installed will vary depending on the type of property you own.

Damp Proof Course (DPC) Injection- This type of system involves a damp proofing injection being installed into the wall of the building which then acts as barrier to stop moisture from rising from the ground above the DPC. Holes are drilled approximately 150 mm above the ground level and the cream injected into the wall.

Electro Osmotic Damp Proofing Course- If using chemicals is not applicable for the property or the property owner requests that a non chemical damp course is used then an Electro Osmotic Damp Proof Course can be installed.

Physical damp proof course made of engineering bricks

The way that it works is that titanium and copper wiring are used to provide a small electric current that runs through the wall and as a result, reverses the capillary action. This ensures that rising damp is kept below the damp proof course.

The primary protection method for damp proofing residential and commercial properties is an injected Damp Proof Course (DPC). This form of protection provides a long-term solution against moisture decay.

To stop moisture from passing through the walls and foundations of the property damp proofing helps prevents moisture and water ingress passing through the interior spaces.

One of the main reasons for having a damp proofing course is to stop moisture affecting the timbers of the property and therefore helping the prevention of dry rot or wet rot.

Where is a Damp Proof Course Applied?

A damp proof course is applied at the lower parts of the walls to restrict the movement of moisture rising up and through the walls.

How Is a Damp Proof Course Installed?

It is important that a damp proof course is installed correctly the first time as not doing so will mean that you will have to pay for unnecessary costs and can also lead to major disruption. One other issue is that the property will be left unprotected against moisture rising up from the ground.

Steps to Installing a Damp Proof Course:

  1. Prepare the wall- Remove damp/salt contaminated plaster
  2. Drill Holes- 12mm holes will be drilled into the wall which will need to be at least 150mm above the ground level.
  3. Install Damp-proof Course- The injection cream will then be inserted into the holes and once the holes are full, these will be capped with either mortar or plastic plugs.
  4. Apply Scratch Coat- Apply a rough coat of at least 5mm thick. This will act as an anchoring layer.
  5. Apply Plaster Coat- Once the scratch coat has become firm, apply the plaster again with at least 15mm-20mm thick.
  6. Finishing Coat- Apply a final skim coat using suitable skim plaster.
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Do You Need A Damp Proof Course Installed?

Do I Need a Damp Proof Course?

A Damp proof course is an important part of the protection for your property to protect it from rising damp, especially when heavy rainfall is a common problem in the UK.

This form of damp proofing provides a long-term solution for moisture breaching the building’s foundation and entering the property. The most common damp problem is being moisture absorption via floors and walls into the side of the property.

Signs That You Need a Damp-Proof Course

There are a number of tell-tale signs of damp being present in walls. The most common signs to look out for are:

  • Black spot mould forming on interior walls. This is a common sign also of a condensation problem.
  • Watermarks on walls formed by either rising damp or penetrating damp.
  • Plaster peeling off walls and damage to other decorative finishes such as wallpaper.
  • Wood, such as skirting boards, will start to deteriorate as a result of coming into contact with moisture.
Penetrating damp on wallRising damp on wallRising damp present on walls in house living room

Should a Damp Proof Course Be Re-Rendered?

If your property has been affected by rising damp then the surface of the walls will be suffering from hygroscopic salts. A damp proof course works by stopping further damage from moisture from rising damp up the walls.

However, it will not get rid of hygroscopic salts that are already present in the render. If the salts are not dealt with then this cause further moisture to be attracted to the wall, thus causing further damp problems. This will fool the property owner into thinking that the damp proof course is not working as it should.

This provides the reason why a DPC should be re-rendered to its original state. The traditional method is to use sand and cement render with a replastering additive added or you could use a renovating plaster.

How Do I Know if My Property Has a Damp Proof Course?

A damp proof course is usually installed at the base of a properties walls during initial construction, with the damp proof course itself being a membrane made from plastic. This form of protection is used to stop damp rising up the walls.

This is the current modern effective modern damp proof course and was originally implemented in the 1970’s. It often entails the incorporation of a plastic strip sandwiched between the brickwork.

Damp Proof Courses were first introduced in 1875 and during this period were using engineering brick, slate or bitumen mixed with mortar.

These earlier damp protection barriers though proved to be unreliable. The type of damp proof coursing installed in older buildings consisted of slate and often were not placed correctly allowing dampness to occur.

Typically, a physical damp proof course lasts for 20-25 years and can fail due to it not being fitted properly or deterioration. If a damp proofing course has failed then this could potentially lead to rising damp.

Rising damp is the movement of moisture through the walls and floors by capillary action. The visual result of rising damp is a “tide mark” left on the walls and plaster peeling off the walls.

Damp is more than likely going to occur in buildings due to leak or an external defect such as blocked gutters or cracking rather than rising damp. This would mean that having an injected damp proof course might not rectify the issue.

Damp Proof Course (DPC) Regulations

The Building Standards introduced requirements that a damp-proof course must meet when being installed in the Site preparation and resistance to contaminants and moisture:

Damp Proofing Course should be at least 150 mm above the ground level unless the design of the building is built that will protect the wall.

The damp course should be continuous with a damp proof membrane.

If there is an external cavity wall then the cavity will need to be placed at least 225 mm below the damp-proof course.

What are the Consequences of Not Having a Damp Proof Course in Place?

Having a damp proofing treatment carried out can prevent moisture from passing through to the interior walls of the property. There are a number of consequences of not having damp proofing carried out at your property.

The degradation of plaster and decorative finishes on the walls can be visually distressing and turn buyers off if you are trying to sell your home as a prospective buyer will be less inclined to buy the property if they believe there are hidden damp issues.

The most serious implication of not having your property damp proofed is the possibility of the dampness leading to timber decaying issues such as wet rot and dry rot.

This occurs from not having the damp treated over a sustained period of time. If left untreated the wood rotting issues can lead to varying degrees of structural damage.

Cost Of Having A Damp Proof Course

The cost of the chemical damp proof course can vary depending on the size of the property and where the dampness is located in the property.

Contacting a damp surveyor who holds the CSRT or CSTDB qualification from the Property Care Association will provide you with the satisfaction that they will provide full accurate advice on getting rid of the damp problem.

Contact a Damp Proofing Specialist

If you want to understand more about solving damp issues in your property, then check out our what is damp? page. If your property is based in either England, Wales or Scotland is suffering dampness or you require an installation of a damp proof course, then get in touch with our damp experts by calling 0800 288 8660 or request a survey online via the link below.

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