What is a Damp Proof Course (DPC)?

Introduction

A Damp Proof Course (DPC) is a protective barrier that helps to keep ground moisture from entering your home.  The ground around your property can become very wet after a rain shower.  This moisture then travels upwards through the ground due to heat from the sun.  Your bricks at the bottom of your home are porous, and therefore not water proof.  Moisture will travel through the tiny pores within the bricks from the outside to the inside of your home.  To stop this a water proof sheet (known as the DPC) is sandwiched between brick, approximately 150mm from the ground.  This prevents the moisture travelling all the way up your brick work.   

  

History of DPC’s in the UK

Historically Damp Proof Courses (DPC) have been constructed from a variety of materials such as lead, asphalt, bitumen and slate.  The materials used for DPC’s have come a long way since DPC’s were first used in the UK in the early 1900’s.  However, damp proof courses only started to become very popular in the 1950’s. These days it is very common for DPC’s to be made from a plastic waterproof membrane. Also, cavity wall construction also helps to prevent moisture penetration, and therefore damp.     

Why are DPC’s Important?

If you have an ineffective or non-existent DPC, then moisture could work it way into your property.  Excess moisture can cause your walls to become damp, which leads to mould build up.  It can even rot away unprotected timbers. There are a variety of DPC’s available, but all have one think in common. They provide a water resistant barrier to help prevent the penetration of damp into your home.

Types of DPC

Plastic DPC

Is a modern DPC that is is typically used for newer houses in the UK. It consists of a plastic waterproof membrane. Below is a polyethylene DPC from the Amazon store.

Chemical DPC Injection

This consists of a water repelling liquid or cream that is injected into the exterior of your wall, 150mm above ground.  For example, silicon is an excellent damp proof course as it is water repellent, and long lasting due to its flexibility.

Membrane DPC

This consists of sheet, usually made from plastic.  It is usually placed beneath concrete slab on ground floors to protect moisture entering your home from the ground. Below is a polythene DPC from the Amazon store. This type of DPC is ideal for concrete floors to prevent raising moisture. You can even use it to suppress weeds, as it will block out the light. Or even as a gravel underlay.

Cavity Wall DPC

A cavity wall could also be considered as a type of DPC.  This is because the cavity helps to prevent the transfer of moisture from your outside wall, to your internal wall.    

Chemical Damp Proof Injection

This method is ideal if your property has rising damp due to a broken damp proof course. It is done by injecting a damp proof cream, which is basically a silicon based liquid. Once injected, the liquid reacts with the silica in the masonry. The result is a water repelling damp proof course.

How DPC’s can Fail

If your damp proof cause is faulty, then it will likely be letting moisture through into your home.  For example, if you see damp patches on your wall up to 1.5m, then this could be a sign of a failed DPC.  Other signs include water damage to skirting boards and wallpaper.  Or the build-up of mould or salts on your walls. The main reason for DPC failure is house movement over a long period of time. This can cause the DPC to break up, especially if the DPC is made from a rigid material such as slate.