Damp Proofing for Basements

How do I know if I have a damp or water ingress problem in my basement?

There are a few ways to tell if you need damp proofing or waterproofing.

Some of the signs include:

    • Water coming in through walls
    • Condensation on walls and floor
    • Blistering walls
    • Groundwater on the floor
    • Rotting columns, headers and joints
    • Damp, humid air

Left untreated, damp basements can cause damage to belongings and as well as increasing the risk of long-term health problems for those living there.

What is basement waterproofing and damp proofing?

Damp proofing a structure below the ground is different from doing so above.

The challenges are different, including water ingress through the floors and walls.

Basements are earth retaining, and suffer from ‘hydrostatic pressure.’

That means there is additional pressure placed on the walls and floors, and so water from outside is pushed against it, causing an internal leak.

A likely result is damage to brickwork and other internal surfaces.


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Why is damp and water ingress in a basement a bad thing?

Basements and cellars that are damp often suffer from poor heating and ventilation.

This is a significant issue because these can contribute to an existing problem if not controlled.

Damp can lead to long-term issues such as dry and wet rot which make a basement uninhabitable.

Ideally, a thorough investigation should be undertaken by an expert to understand the cause.

Furthermore, external defects in a building can cause additional problems by letting in more water through cracks, and so a certified installer of damp and waterproofing products should be commissioned.

Systems to waterproof your basement

There are three types of waterproofing systems that exist for below-ground structures.

The British Standards, edition BS8102:2009, specifies that they should be waterproofed using two lines of defence.

They are:

Type A – An external barrier method

Type B – Structurally integral, or waterproof concrete

Type C – A drainage system, most commonly a cavity


In existing structures, the most common method of waterproofing is usually a cavity drainage system.

The type of waterproofing you require will depend on what you use a basement for.

You will need less waterproofing, for example, for a plant room or a car park than you would for a full office building.

For example, if a basement is used as habitable space you will require a full tanking system consisting of two lines of defence.


Cavity drain membranes

A cavity drain membrane is studded.

Usually, in a basement that consists of two types of defence, it exists in the event an external waterproofing method fails.

When that happens, a cavity drainage membrane redirects water that has entered the building to a sump and pump system or an external land drain.

A sump and pump system should also be fitted with an alarm and battery back-up to alert you if it fails.

If it does, a licensed contractor will need come and replace it.

A sump and pump systems should also be serviced annually by the contractor that installed it.

Cavity drainage systems can be handy if your existing basement has water ingress and you need a remedial measure.

When choosing this method, or when waterproofing a basement in general, you must ensure the work is done by qualified experts.

If you are building a new basement, it is recommended by British Standards that a CSSW (Certified Surveyor in Structural Waterproofing) surveyor be involved with the design.

Cavity drain membranes

Tanking refers to applying a liquid waterproof coating, such as a slurry, to walls and floors of cellars.

It is a Type A system, and is an ideal way of treating damp on walls because it stops water getting in.

A waterproof slurry works by blocking water from entering, which is where it differs from a cavity drain system that allows water come before redirecting it out again.

A waterproof coating must be applied to undamaged walls, and the installer must pay attention to weak points such as wall-to-floor joints.

A tanking slurry is also often referred to as a cementitious coating or tanking.

It can come pre-mixed, or in a powder form that is mixed with clean water at the property.

It should result in a smooth concrete wall surface.

At this stage it is important to note that it is not recommended to tank an entire basement with liquid waterproof paint.

However, it is possible to combine a tanking system with a cavity drain one for extra protection.


Condensation is a common issue in basements because they are generally damp and dark places without any waterproofing.

It occurs when wet, warm air meets cold basements walls and floors.

After cooling on impact, it causes moisture to remain in the air.

Luckily, condensation is usually easier to deal.

Before doing anything, you should check the exhaust on your dryer and drain central air conditioners.

Make sure they aren’t blocked and are working properly.

Both create excess moisture which enters the air and causes condensation.

If there is a bathroom or kitchen in the basement, it’s worth considering whether to install an exhaust fan.

Bathrooms with showers, or hot water from kitchens can be a source of condensation because they generate additional moisture.

Try sealing your drier ducts too – another route for warm, moist air to seep into a basement.

You can do so by using a rigid metal duct and have it run the shortest possible distance to outside.

Air circulation should be considered, and installing vents can help.

Try to improve all ventilation, even opening a window or doors on occasion.

That only works when the air outside is drier than that inside.

A dehumidifier can help to reduce condensation too by getting rid of moisture in the air.

That is handy when humidity is high, less so if required all the time.

Finally, insulating a basement in areas where condensation occurs can help massively.

Consider covering places such as walls, ducts and pipes which will assist with stopping warm air from touching cooler surfaces.



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