London Waterproofing Solutions Ltd              020 3794 4200

London Waterproofing Solutions Ltd


Tel: 020 3794 4200

Early Warning Signs of Groundwater Flooding

A street in London in the rain
Flooding is a concern for many homeowners, especially when autumn closes in. For a number of people, the focus is on surface water flooding, where a sudden increase in river levels can lead to burst banks or waves and spray can cause coastal flooding.  Groundwater flooding, however, is an ever-present danger that homeowners and businesses need to be aware of. It has a much slower rate, sometimes taking days, weeks, or even months to happen, and can last for just as long.

Many flood defences focus on what to do in the event of river flooding, but groundwater flooding presents different challenges and traditional flood prevention methods do not work as effectively against groundwater. How will you know if your home is at risk of groundwater flooding and what can you do to minimise the risks?

What is groundwater flooding?

Groundwater flooding occurs when levels of water in rock and soil or underground rise. Known as the water table, these levels can rise steadily over an extended period, sometimes taking months to appear. As the water table rises it can reach ground level and come through to the surface. This is when groundwater flooding can occur.

Perched water tables are increasingly common. This is where there is a temporary rise in the groundwater level as a result of rainfall, a damaged drain or mains water burst.

Groundwater tends to be noticed when it appears in low-level rooms, such as cellars or basements, as it comes through the floors from the ground and into your home. Traditional flooding prevention does not work as effectively against groundwater flooding, as the water comes through the ground and into your home, rather than over the surface.

Where is groundwater flooding most common?

There are certain areas of Britain more at risk of groundwater flooding. Traditionally, people associate rural spaces with groundwater. Valleys are some of the more common areas, but groundwater can also emerge on hillsides. However, cities are not immune. It can occur in areas with chalk, sand, and gravel.

London has a big problem with groundwater flooding. While homes all over the city are affected, it has become a significant problem for homes in Fulham, Hammersmith, Southwark, and Wandsworth. Heavy rainfall and rising groundwater levels are just some of the factors leading to basements and cellars flooding slowly over time.

Waterproofing your home against basement flooding is important, but it is also vital to recognise the early signs of groundwater flooding so you can take the necessary steps to minimise damage as quickly as possible.

Warning signs to watch out for

River flooding, coastal flooding, surface water flooding, and reservoir flooding are all very different to groundwater flooding. When most people think of flooding, they imagine streets filled with water or the water coming into the home via doorways. Groundwater is a different matter entirely, and can severely damage your property and disrupt your life. That said, there are a few early warning signs that can alert you to potential flood risks. 

  • Damp patches appearing in lower levels of the property
  • Water in your cellar/basement with no source
  • Local sewers overloading and overflowing

The code of practice that covers flooding in below ground structures states that a risk of flooding must be assumed for any basement or cellar, so even if there aren’t any signs now, problems can occur in the future. Recent weather events have exposed many unprotected basements, therefore if your basement is currently unprotected then now is the time to consider waterproofing it.

How do you manage groundwater flooding?

Flooding prevention is different, depending on the type of flooding you want to protect against. Traditional methods of flood protection, such as sandbags, do not work as effectively against groundwater. Sandbags prevent water from rushing into an area, while groundwater can slowly rise, come up through the floor, and remain at a high level for an extended period.

When it comes to managing groundwater flooding and protecting your home, there are different options available to you. Which one is best suited to your property will depend on a number of factors, so consulting a CSSW qualified surveyor is the best way to ensure the perfect solution for you.

Type A Barrier System (Tanking)

Tanking is when a tanking slurry or waterproof render is applied to the floors and walls of lower-level rooms, creating a barrier between your home and groundwater. While this is an approved method for groundwater protection of your basement, it can be a challenge, especially with older buildings. Reliance on a tanking system alone is not generally recommended.

For a tanking render to work effectively, a good bond must be created, and with many of the current properties in London, the basements and cellars have been constructed with brick. Getting a good bond to brick can be a challenge. If the bond is not obtained, this can lead to failure of render coats, dampness, and potentially flooding if it fails. Structural movement can also cause renders to crack.

Type C Cavity Drainage Membrane

One of the most popular solutions is the Type C cavity drainage system, which is an industry-standard. Recognised as the more reliable system, it is a must for many London homes where a tanking system will not work. One key advantage of this system is that it can be flood tested before the system is commissioned, so you know it will work.

A polymer studded membrane is installed to the floor and walls, with drainage channels leading to a sump and pump or existing drainage system. This manages the water entering the basement by moving it away from the property. As it requires little to no preparation of the walls, it has become a favourite for many homeowners looking to transform their basement or cellar into a useable room.

Why groundwater flooding is a risk you need to be aware of

There have been many flood maps created for the United Kingdom, with many focusing on the city of London. However, these maps tend to focus on surface water and river flooding. There are currently no groundwater flood maps, as the risk of flooding can vary drastically over time. The steady build-up of the water table means that your property may not flood immediately. Water can appear in your basement days, weeks, and even months after the levels begin to rise.

It is a hidden but ever-present danger in London, and preventing it is the best way to ensure the safety of your home. At London Waterproofing Solutions, we offer free waterproofing surveys for those looking for the right solution. Simply fill in your contact details and we will be in touch.

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