Why basement waterproofing is 'now as much about climate resilience as it is about comfort,' and how to get it right

Waterproofing a basement is arguably the most important thing you can do with a subterranean space.

And it's not just something that you need to do if you plan on carrying out a basement conversion to create a new habitable space – even if you only want to use it for storage, you will want to ensure it remains dry and free from damp and mould.

There are several methods when it comes to basement waterproofing and the process you choose needs to be suited to your particular basement – what is suitable for one structure won't necessarily work for another.

We asked the experts to explain the various options for waterproofing a basement properly, as well as how much to budget.

Why is basement waterproofing important?

Whatever your basement ideas involve, waterproofing is crucial – for several reasons.

'Waterproofing a basement isn't just about comfort – it protects your home’s structure and your health,' picks up Paula Higgins, CEO of HomeOwners Alliance. 'Without it, hydrostatic pressure (water in the soil around your home) can push moisture, or even water, through cracks in walls and floors, leading to dampness, mould, rot and potentially serious structural damage.

'Basement waterproofing is no longer a “nice-to-have” – it’s becoming an essential step in protecting homes against the UK’s changing weather patterns,' continues Paula. 'Extreme rainfall means more water pushing against your basement walls and floors, increasing the chance of leaks and dampness.

'Whether you plan to convert your basement into living space or simply want to safeguard it, waterproofing is now as much about climate resilience as it is about comfort.'

Paula Higgins

After spending 15 years reforming housing policy in government, enough was enough. Homeowners needed a voice and HomeOwners Alliance was born.

How do you waterproof a basement?

There are several methods that can be used to waterproof a basement and in some cases this might be determined by basement conversion building regulations.

'Basement waterproofing can be done in a number of ways,' explains architect Tina Patel of Architect Your Home. 'You have Type A, B and C and how you tackle it should be considered in terms of your initial outlay – some systems will not last as long and result in the process being needing to be redone after five or 10 years – so although this may sound cheaper at outset, it is unlikely to be in long run.'

These methods of waterproofing are also known by other terms.

Type A: Tanking

Type A is also known as 'tanking' and is a barrier system.

'With tanking, a bonded cement layer is applied to the walls and floors to withstand external water pressure,' explains Paula Higgins.

This waterproof layer forms a barrier between the basement and any groundwater surrounding the structure. It can be applied to the internal or external surface and even between floor and wall surfaces – something known as 'sandwiched waterproofing'. For double protection, waterproofing materials can be applied to both the internal and external walls.

Pros:

• Straightforward solution
• Can be applied to existing structures

Cons:

• If not done properly, leaks can occur
• Not best in areas where there is a high water table where the water pressure can push through any faults in the system

Type B: Structurally integral waterproofing

This is a method most commonly used for new basements and is carried out during the building process, where a moisture-impervious concrete is applied to all surfaces.

Pros:

• The structure itself is the waterproof barrier so no additional barriers are required
• Long-lasting and robust

Cons:

• More expensive
• Hard to retrofit
• Poor installation can lead to weakness in the system

Type C: Cavity drainage system

Cavity drainage systems are often considered one of the best ways of waterproofing a basement. Rather than preventing water from entering your basement through barriers, they safely channel it away into drainage channels that then take it into a sump and pump system. Finally, the water is taken to an external drain.

'Type C involves a cavity barrier system and is often preferred as it allows water in but can mitigate its impact on the surrounding vicinity,' further explains Tina Patel.

The great thing about these systems is that they are easy to retrofit and can even be installed in basements where a previous waterproofing system has failed.

Pros:

• Easy to install
• Can be combined with other waterproofing systems
• Easy to access for inspection

Cons:

• Failed sump pumps can cause issues
• Channels need to be maintained to keep them blockage-free

Tina Patel

Tina Patel is a RIBA-chartered architect and director at Architect Your Home, with over 15 years' experience helping families transform their homes through thoughtful, stress-free design. She specialises in homeowner-led renovations, making the process of extending, refurbishing, or reconfiguring a home simpler and more empowering. Having worked on over 200 projects, Tina is passionate about creating happy, harmonious homes that add real value to family life. She's an expert voice on planning system challenges, permitted development, and the realities of renovating in the UK today – especially from a homeowner’s perspective.

Can I waterproof a basement myself?

Although some people do attempt to waterproof a basement on a DIY basis, this really is not something that any of the experts I spoke to recommend – in fact it usually leads to expensive and damaging basement conversion mistakes.

'It is specialist work and not something that should be done by your main contractor,' points out Tina Patel, who goes on to point out that it is wise to use the services of a Certificated Surveyor in Structural Waterproofing (CSSW).

'A CSSW will consider the risks involved with water ingress and consider how to mitigate these,' advises Tina. 'Some suppliers have internal CSSW teams although, equally, you can engage an independent design team – just ensure that all respective parties have insurance.

'You should also hire a team that can provide insurance backed warranties – this means that if they go bust you would still have some protection,' adds Tina.

FAQs

How much does it cost to waterproof a basement?

There are so many factors that can influence basement waterproofing costs that it is hard to give an exact figure.

'Estimating costs is notoriously difficult as there are so many factors to consider,' picks up Paula Higgins. 'The company will likely need to do a survey first.

'As a general guide, expect to pay £100- £120 /m2 to waterproof walls and floors. A small basement (4m x 5 m) could cost £8,000, compared to £17,500 for a larger 6m x 7m basement.'

How long does it take to waterproof a basement?

Of all the things you need to know before converting a basement, average timescales is one. The length of time it takes to waterproof a basement very much depends on the type of structure in question and the system being employed.

'Simple conversions using a cavity membrane plus a sump pump system can be completed in 2–3 weeks, including sump excavation and pump installation,' explains Paula Higgins.

'Major projects – such as lowering floor levels, underpinning, or excavating new basement spaces – are more time-intensive and costly and typically take several months.'

You'll also need to ensure your basement is adequately ventilated to keep it comfortable and dry.