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Damp Proof Course (DPC)

A Damp Proof Course (DPC) is one of the most common forms of protection from rising damp. In this guide, we will explain what a damp proof course is, how it works, and why it is needed to prevent damp and other related property maintenance concerns.

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Do You Want Help with a Damp Proofing Solution?

If you are concerned that a property you own does not have a damp proof course, or your existing damp proof course has failed, get in touch with our team to find out if your property is protected against damp, and what can be done if it isn’t.

The best way to get in touch with us is by filling in our survey request form – just type in your contact details and a brief description of your concerns, and one of our friendly team members will contact you to assist you with your query and arrange a property visit with one of our expert surveyors.

Prefer to speak over the phone? You can reach us at 0800 288 8660 to discuss your concerns with our service team.

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An external damp proof course with no visible defects

What Is a Damp Proof Course?​

A damp proof course is a protective barrier installed into the lower section of a wall during construction. Every damp proof course works the same way, providing a waterproof barrier that prevents moisture from rising through a wall and appearing on the interior surface.

Most damp proof courses are installed individually, and you’ll usually only see one method in use at a time. However, if there is no existing damp proof course in place, or if the existing damp protection has failed, then this leaves a building vulnerable to rising damp problems.

What are the Different Types of Damp Proof Courses?​

There are various types of damp proof courses that can be present depending on the age of a building. Some of the more common types include;

  • Slate, a traditional moisture barrier known for its durability. Slate DPCs first became a widespread legal requirement in the UK following the Public Health Act of 1875, and were installed regularly up until the early 1940s. Prone to failure due to being installed incorrectly during initial construction.
  • Bitumen, an oil-based barrier usually soaked into felt, hessian, or reinforced fibre linings. Bitumen DPCs were installed regularly between the 1920s and 1980s. Bitumen can also be applied on the surface of walls as a tanking solution for below-ground rooms or walls that suffer from water ingress.
  • Damp Proof Membranes, usually in the form of plastic sheeting. More common in constructions from the 1980s and beyond, and regularly used in new-build properties today.
  • Chemical Injection, a method used to replace a damaged or defective DPC post-construction. A chemical cream is injected into the mortar joints at the foot of a wall, which then spreads and hardens into a waterproof barrier. First used around the 1950s, chemical injection became the industry standard damp prevention method in the 1990s with the adoption of silicone-based creams.
  • Electro-Osmotic Systems, a modern method used in heritage buildings where conservation is the primary concern. Involves embedding a series of electric probes and wires into a wall, which then carry a current that reverses capillary action within a wall. First used in the early 1970s, and still used today in conservation projects as a non-invasive damp proofing solution.

How Does a Damp Proof Course Work?​

A damp proof course is usually installed in the mortar joints of a wall during construction. Once installed, this barrier prevents capillary action, where moisture travels through small spaces in porous materials like brick or concrete. This stops water from rising past a certain point and showing as damp patches on the interior wall.

Damp Proof Course Installation 2048x1536 1 Timberwise

What are the Signs You Might Need a New Damp Proof Course?

You might require a new damp proof course in your property if you notice some or all of the following symptoms:

The Timberwise Chemical Damp Proof Course Treatment Process

First, you should have a specialist damp and timber surveyor attend your property to assess the likely causes and symptoms of any property maintenance issue. Early and correct diagnosis will confirm the treatment required, and will prevent unnecessary and extensive repair work. You can request a survey to have one of our expert surveyors attend and diagnose your property. 

Upon completion of a survey, our surveyors will provide a summary of identified defects in your property, and provide a quote for remedial work to repair them.

Upon acceptance of our quotation, our technicians will attend your property to install a chemical injection damp proof course using the following method:

  1. Clear the affected wall plaster to remove any historic salt deposits and allow access to the masonry.
  2. Identify the first mortar joint above external ground level, and drill small holes at regular intervals throughout the mortar joint along the wall.
  3. Inject a silicone-based chemical cream into each hole.
  4. Cap each hole with fresh mortar or plugs to seal them.
  5. Once the mortar has dried, re-plaster the wall surface with a salt-retardant specification plaster to prevent future atmospheric moisture ingress.

Further information on this treatment is available on our Damp Proof Injection page.

What are the Benefits of a Professional Damp Proof Course Installation?

There are several benefits to having a professional damp proof course installation in your property:

  • Professional surveyors correctly identify and treat the type of damp without unnecessary repair work. 
  • Professional damp proof course installations protect the structural integrity of a property.
  • Professional damp proof course installations improve air quality by creating a barrier against rising damp, which prevent the conditions ideal for mould and fungal growth.
  • Proactive damp proof course installations are often significantly more cost effective than repairing extensive damage from fungal decay.
  • Dry walls are more effective at insulating a property, reducing your heating bills.
  • A dry home is more attractive to potential home buyers when selling your property, protecting its resale value.
  • As a PCA-accredited property preservation company, Timberwise is required to provide the best practice and guidance to our clients, no matter the scale of work involved to remedy a property care concern.
  • Timberwise uses environmentally friendly products that have been rigorously tested by the Health and Safety Executive.
Timberwise surveyor inspecting damp proof course in Glasgow

Costs and Guarantees​

The cost of a new damp proof course will vary depending on the size of a property and how many walls are affected by rising damp. Upon completion of an inspection, our surveyor will provide you with a detailed report of any identified defects and an estimated cost to install a damp proof course alongside any additional repairs required to restore the property.

All Timberwise repairs and treatments carry long-lasting, insurance backed guarantees to provide peace of mind and ensure the success of your new damp proof course for at least 20 years.
Damp Proof Course Timberwise

Damp Proof Course FAQs

How Long Does a Chemical Damp Proof Course Last?​

A silicone-based chemical injection damp proof course can last between 20 to 30 years. This is provided the system is installed correctly by a professional property preservation specialist, and remains well maintained and regularly monitored for defects or during structural changes to a building. All new Timberwise chemical damp proof course installations also come with a 20-year guarantee to ensure their longevity.

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Will I Need to Redecorate After Having a Chemical Damp Proof Course Installed?​

Yes, you will need to redecorate upon completion of a damp proof course installation. It is necessary to remove up a 1m high band of plaster along any wall that is suffering from the effects of rising damp. This process not only removes any damaged plaster, but also any historic salts, which can draw atmospheric moisture into the plaster and lengthen drying periods or cause the plaster to fail. Upon completion of a damp proof course installation, a wall will be replastered with a salt-retardant specification, which can be redecorated to your preference upon completion of a suitable drying period.

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Can I Install a Chemical Damp Proof Course Myself?

Yes, it is possible to install a damp proof course yourself, and it can be a more cost effective method of managing rising damp. The two most common methods are through chemical injection or by inserting damp proofing rods into a damp wall. However, DIY methods are also riskier, and do not come with the same long-term guarantees as a professional property maintenance service. DIY methods are also more prone to user failure, and not diagnosing a damp issue correctly could lead to incorrect treatment or worsening an existing damp issue.

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Where is a Damp Proof Course Applied?​

A damp proof course is applied at the lower parts of the walls, usually in the first mortar joint (at least 150mm) above the external floor level.  This continuous barrier prevents the movement of moisture rising up and through capillaries within the walls.

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

A damp proof course is usually installed at the base of a property’s walls during initial construction. Often, it’s possible to identify a damp proof course as a thin line of different material between exposed layers of brickwork. For example, a slate or bitumen DPC is often instantly recognizable as a thin black strip within the lower section of a wall.

However, as processes and techniques have improved, it’s gotten easier to disguise a damp proof course within a wall. For example, modern plastic membranes can easily be hidden within the mortar joint. The same is true of a chemical injection damp proof courses, where the drill holes can be covered with mortar or plastic caps once dry. The only evidence of an installed chemical DPC might be drill holes in bricks, which is a sign of an incorrect installation.

For a full list of Timberwise guarantees, and the relevant terms and conditions, visit our guarantees page.

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Do I Need a Damp Proof Course?​​

A Damp proof course is an important part of the protection for your property, protecting it from rising damp, especially in areas of the UK where groundwater flooding and heavy rainfall are key risks.

The most common damp problem is moisture absorption through walls and into adjacent timber structures such as floorboards. Prolonged exposure to moisture can allow fungal decay such as wet rot or dry rot to germinate. Dry rot is especially invasive, and can spread behind plaster or over walls to infest other timbers.

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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, timber decay issues can lead to varying degrees of structural damage.

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Can Cavity Wall Insulation Cause or Worsen a Damp Issue?​

Yes, cavity wall insulation can cause or worsen damp issues. However, this is only typical if it is installed incorrectly, in an unsuitable property, or if existing damp issues were ignored prior to installation. If the exterior walls of your property are weatherproof and free of defects, then there’s usually no concern, and you can enjoy the benefits of a warmer home. However, if moisture seeps into the insulation from a leak or defect, this can create a bridge for moisture to appear on your internal walls, creating areas of penetrating damp.

To help you identify if you are at risk of damp issues as a result of installing cavity wall insulation, we have compiled a list of questions below to see if your house is at risk for potential damp issues from having cavity wall insulation installed:

  • Are the external walls poorly constructed or maintained?
  • Are the rainwater goods on your property working without leaking or overfilling?
  • Is the property exposed to heavy moisture levels from flooding, coastal moisture, or heavy rainfall?
  • Is the house sheltered by buildings or trees?

If you answer yes to any of these questions, then you may need to remedy any external defects prior to installing cavity wall insulation in your property. If the property looks to suffering from penetrating damp issues resulting from cavity wall insulation, then check out our penetrating damp treatment page for helpful tips on reducing the damp problem.

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What are the Building Regulations Around Damp Proof Course (DPC) Installations?​​

The British Standard relating to damp proof courses is BS 8215.1991, the Code of practice for design and installation of damp proof courses in masonry construction. This document provides guidance on selecting materials for a damp proof course, and ensures DPCs are properly positioned for complete protection against ground moisture and water ingress.

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Need Further Assistance on Damp Proof Courses?

If you think you need a damp proof course and you are looking for a specialist to fix the problem, then our Timberwise team are here to help. You can get contact us by requesting a survey, or calling us on 0800 288 8660.

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Timberwise (UK) Limited is an Introducer Appointed Representative (Financial Services Register No. 418778) of Phoenix Financial Consultants Limited (Phoenix). Phoenix is a credit broker, not a lender. Phoenix is authorised and regulated by the Financial Conduct Authority (FRN: 539195), and offers finance from its panel of lenders. All finance subject to status and credit checks.