A damp proof course is an essential part of a building’s construction. Intact, effective damp proofing prevents a whole host of issues, from structural collapse to residents’ ill health. If you have concerns about the state of your property’s damp proof course, you might consider remedial work, but how do you know if it is needed, and is it worth the expense? Find out more…
What is a damp proof course (DPC)?
A damp proof course is a waterproof barrier in walls to stop moisture rising up through the building. When a property is built, one of the different types of damp proofing will be installed.
Over time, a damp proof course can fail, leading to issues such as damp, rot and potentially even structural damage. It is important to know the signs of a compromised damp proof course and to take action to repair/replace it if necessary.
How does damp proofing work?
A damp proof course is usually located 150mm above (approximately Z brick courses) ground level, horizontally within the walls. It acts as a barrier to stop water seeping up the walls.
Why is damp proofing important?
Damp can lead to many different issues including:
- Health issues such as respiratory problems and allergic reactions.
- Wet rot – a fungal growth which weakens timbers.
- Dry rot – a fast-spreading rot which damages timbers beyond the damp area.
- Structural problems caused by rot which could ultimately make the building unsafe and/or unattractive to residents and potential buyers.
Damp proofing helps protect against all of these issues and is essential to the health of a building.
Common types of damp proof courses
There are different types of damp proof courses used in the construction of buildings and some can be retrofitted if necessary:
| Type of DPC | Material | Installation method | Pros | Cons |
| Membrane | Plastic e.g. polyethylene | Laid under floors | Inexpensive, easy to install, effective | |
| Bituminous | Bitumen/asphalt | Applied as a coating or sheet | Durable, long-lasting | |
| Slate | Slate | A layer of slate is laid within the wall/under flooring | Natural, long-lasting | Relatively expensive |
| Chemical injection | Silicone-based chemicals | Damp proof course injection into masonry walls creating a waterproof layer | Cost-effective, quick process, a remedial option | Success depends on the condition of the walls and skill of application |
| Electro-osmotic | Electrical current | An electrical current is passed through electrodes into the wall causing water to be drawn away | Varying results, salts may build up in the walls | |
| Lead | Lead sheet | Most often used as flashing i.e. at junctions or around openings | Durable, effective, flexible | Potential for corrosion, relatively expensive |
| Cavity wall | – | Creates a cavity or space between walls, acting as a barrier to prevent moisture seepage | Improper installation may result in damp | |
| Plaster | Plaster with waterproofing additives | Applied to interior walls | Simple, inexpensive | May not solve damp issues |
| Ceramic cylinder | Tubes of fired clay | Installed within walls to block liquid water but allow water vapour to escape | Reliable, effective, can be remedial |
How do I know if my property needs a damp proof course?
If your house was built in the last 100 years or so it should have been built with a damp proof course, but you may discover a new one is needed. Age, physical damage or improper installation could lead your damp proof course to fail, and you may suffer from rising damp, signs of which include:
- Damp patches and/or ‘tide marks’ on walls
- Peeling wallpaper/paint
- White/greyish marks: salt deposits on walls as water evaporates leaving minerals behind
- Damaged skirting boards
- Mould
- Damp smell
- Bubbling plaster as it absorbs water
- Rotting wood, especially near the ground
If you spot any of these signs, a surveyor can identify the cause, determine if the damp proofing is compromised and suggest what action is necessary.
Cost of damp proofing
The cost of damp proofing depends on many factors including the size and location of the property, the scale of the problem, the type of remedial proofing chosen etc. When you get a damp proofing cost quote, remember to factor in additional costs such as plastering, painting and waste removal (some companies include this).
DIY vs professional damp proofing company
It is sometimes possible to install damp proofing yourself, but a carefully chosen professional will have the skills, experience and expertise to do the job. More importantly, reputable damp proofing contractors will offer a long-term insurance backed guarantee for their work which will transfer with title, meaning future owners of the property will benefit from the treatment if you sell the property on.
A Chartered Surveyor can help you understand the severity of the problem as you decide how to proceed.
How does damp affect property value?
If you are selling your property and damp if discovered, many buyers will immediately be put off purchasing. Damp can hint at larger issues and indicate additional expense down the road.
If a buyer decides to continue, they are likely to want you to address any damp discovered or ask for a discount to reflect the work needed to rectify the problem.
If you are concerned your property is suffering from dampness, we would recommend establishing the presence and cause before putting your house on the market.
Damp survey
If you are concerned about damp, a damp survey by a trusted surveyor will identify the severity, cause and required action. While Level 2 and level 3 property surveys cover damp, it is worth booking a specific damp survey if you have concerns.
Your damp surveyor will:
- Inspect inside for signs of damp e.g. mould, stains and condensation.
- Inspect outside for sites of ingress, damage and issues such as blocked gutters.
- Use a moisture meter to measure levels of moisture in floors, walls, and ceilings, below sanitaryware and flat roofs above.
- Assess the level of damage.
- Use their expertise to identify the cause of damp.
- Provide a comprehensive report including the type and extent of damp, potential cause and best next action.
Get in touch
Effective damp proofing is essential to protect a building from rising damp, maintain its structure, prevent health issues and to comply with Building Regulations. An effective damp proof course will also preserve the value of your property.
If you are concerned about the status of your damp proof course or have noticed any signs of damp, ask a surveyor to conduct a damp survey. They will help you understand any issues, causes and what action is needed.
At Trinity Rose, our team of experienced Chartered Surveyors are skilled in carrying out damp surveys. If you have any questions or would like to book a survey, please get in touch and we will be happy to help.