London Waterproofing Solutions Ltd              020 3794 4200

London Waterproofing Solutions Ltd


Tel: 020 3794 4200

Groundwater Flooding in Basement: Questions & Answers

Shard of the Mordor, London, cityscape at night time

There are different types of flooding, but one that many cities across the UK are struggling with is groundwater flooding. Homes in London, particularly in Hammersmith, Fulham, Southwark, and Wandsworth are the most affected by it, with rising groundwater levels causing problems.

The issue is that many people don’t know enough about groundwater flooding to act against it. News articles about flooding focus on river flooding, but groundwater acts differently, and the preventative measures against this type of flooding aren’t as effective against it. Here at London Waterproofing Solutions, we answer the most common questions about groundwater flooding.

The basics of groundwater flooding

What is groundwater flooding?

Groundwater flooding is different to surface water flooding. It occurs when the levels of water underground or in soil and rocks rises. This is known as the water table, and it can rise steadily over a period of time, sometimes taking a number of months or even years to reach flooding level. When it does reach ground level, it can penetrate through the surface and come into homes and businesses.

How common is groundwater flooding?

Although flooding is quite a common risk for homes and businesses, groundwater flooding is not as common, with around a few hundred thousand properties affected by it in the UK each year, as opposed to the 2 million properties in flood-risk areas. For this reason, many homeowners and businesses are unprepared for it.

What causes groundwater flooding?

The water table in the ground can rise up, with water in the ground, rocks, and soil reaching ground level. This build-up tends to occur following high rainfall, as the rain water will penetrate the ground and steadily rise to the surface.

How long does it take for the water table to lower?

It can take a significant amount of time for the water table to lower and for groundwater flooding to cease. As the water builds up steadily over time, it does not flow away as easily, and so groundwater takes a long time to subside. It can take several weeks or months, depending on the area.

Where does groundwater flooding happen?

Groundwater flooding can happen anywhere, but it is more common in areas near a water source, such as a river, a lake, or a marsh, or in areas with low-lying permeable rocks. London is one of the UK cities most at risk of groundwater flooding, as a result of the River Thames and the ground upon which the city stands.

Clay-based soils present a high risk of groundwater flooding.

As water percolates into the ground, it doesn’t drain away freely, sitting against the structure.

The resulting hydrostatic pressure exploits weaknesses in the structure, causing the basement to flood.




Taking measures against groundwater flooding

Does groundwater flooding come through walls?

Homes and businesses can flood through walls as the water finds the weakest points in the property. As the water table slowly rises, you’ll often find that your home floods through the floor. However, if you have a basement, the groundwater can work its way into your home through any weaknesses in the walls.

How do you remove groundwater flooding from a property?

A drainage or pump system can be used to divert groundwater away from your home. By redirecting it from your property, you can prevent the water from working its way into your house. However, if there is too much water, a pump may not be as effective.

How can groundwater flooding be prevented?

Keeping groundwater out of your property is easier than trying to remove it. Effectively waterproofing your home is the key to achieve this, either through a barrier system (tanking) or through a cavity drainage membrane. The solution right for your home will depend on your needs and future plans for your home.

Is groundwater flooding covered by insurance?

Groundwater flooding is covered by some insurers as standard. It is important to read the fine print of your policy and check which types of flooding is covered. Some insurers will cover only one type. You will want to seek out an insurer who covers this if your home or business is in a groundwater flood risk area.

Who is responsible for groundwater flooding?

Local Authorities have a responsibility to manage the risk of flooding as a result of groundwater, while the Environment Agency will provide groundwater alerts and warnings when homeowners and businesses need to prepare.

Is your home at risk of groundwater flooding?

Homes in London, and especially those in the Hammersmith, Fulham, Southwark, and Wandsworth areas, are more at risk of flooding from groundwater. This is not only because of the River Thames, but also the ground upon which London has been built.

The problem is that groundwater flooding can be more difficult to prevent than surface water flooding. With surface water flooding, many people are able to protect their homes by building flood defences or using sandbags as a barrier. These solutions do not work for groundwater, which is why it is best to speak to experts about the right option for you.

Waterproofing solutions you can trust

The BS8102:2022 Code of Practice is for protection of below ground structures against water from the ground. This code of practice provides recommendations and guidelines for dealing with groundwater, such as waterproofing, watertight construction, and drained cavities, as well as the evaluation of conditions and risk assessment of the property. All of our CSSW qualified surveyors used this code of practice, so you know that you are in safe hands.

If your home is in London, you could be at risk of groundwater flooding. Don’t take the chance – book your free survey now! You’ll receive a detailed report to help you understand which waterproofing solution is right for you.

Got some more questions about groundwater? Contact us now for honest and professional advice.



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