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Waterproofing Your Basement Conversion: Transform Your Space with Confidence!

waterproofing basement

Basement conversions are becoming increasingly popular as residents across the UK look to find new and creative ways to enjoy their space while adding value to their property. Some estimates suggest you could enjoy up to a 20% increase in the value of your property, while it could be up to 50% in London. 

There are fantastic ways to maximise the space below your property, from open-plan lounges with an industrial look and boutique-style bathrooms to wine cellars for storage and tastings and full-kitted games rooms for the kids. 

However, there can be no worse feeling than spending all the time and money getting the perfect finish on your new space, only to find the harmful effects of damp attacking your basement.

Unfortunately, we are regularly called in to fix issues where water has entered the basement. Damp can occur for many reasons, such as condensation build-up from poor ventilation to poor drainage around the house’s perimeter, plumbing leaks in or around the basement or even cracks in the walls and floors. 

While dampness can seem like a trivial issue that people often ignore, its impact, particularly in the basement, can be far-reaching. It can lead to structural issues, weaken foundations, provide the perfect conditions for pests to flourish, and even increase energy costs as you battle to combat the challenges of high humidity.  

So, if you are considering converting your basement or it is in the plans for a new build, there are a few things you want to consider to ensure your home below ground remains watertight.

What is Basement Waterproofing?

As you might have guessed, waterproofing your basement means ensuring that the section of your house below ground repels moisture and is an enjoyable space for your family. 

Unfortunately, we see examples of poor practice in these areas, often a patch-up job for issues not addressed during the initial build. Many examples of poor work result from homeowners not being fully aware of the process and knowing what questions to ask their contractors.

There is a British Standard Code of Practice (BS8102:2022) set out by many of the leading bodies in the industry that provides guidance and recommendations on the best approach for protecting “below-ground structures against water ingress”.

It outlines the three main approaches that should be adopted:

TypeA – Creating a waterproof barrier to the structure

TypeB – Structural integral watertight construction

TypeC – Drained cavity construction   

TypeA – Creating a waterproof barrier to the structure

This is a common approach to waterproofing on a new build home. Often referred to as tanking, the idea is to establish a protective barrier between the surrounding moisture and the inside of your house. 

The types of barriers can vary from bonded sheet membranes to mastic asphalt membranes, among many others. The success of this approach is dependent on the quality of the barrier used and its application. 

With a high water table, moisture is constant; therefore, any fault in the barrier will allow water to penetrate the porous elements, such as masonry. 

The challenge with this approach is that it requires access to repair faults, which should be considered when applying. If it is retrospectively applied, adding a protective barrier internally will help identify and fix any future faults. 

Adding an external barrier is common in new builds and is perfectly acceptable, but should any issues arise, some excavation may be required to solve the problem.    

Therefore, thoroughly inspecting the current situation and working with a waterproofing designer will ensure you get the most appropriate solution. 

TypeB – Structural integral watertight construction

The Type B approach requires the structure to be waterproof rather than adding anything to the building. 

Type B is quite a technical approach to waterproofing a basement and is generally reserved for new builds. The success or otherwise relies heavily on the accuracy of the design and build. 

Concrete is typically used as a barrier as, by its nature, it is naturally waterproof. However, it is vital that the right, low-permeable concrete is used and that, through careful construction, the joints have minimal defects. 

There are two approaches to strengthening the concrete used. 

  1. Using steel reinforcement bars to control any cracking preventing the movement of water.
  2. Using admixtures which essentially block the pores in the concrete when they come under pressure from the water.  

Type B waterproofing systems typically fail due to defects in the installation. This approach should be installed ‘under licence’ of the supplier or manufacturer; however, corners are often cut, and those installing it must have the right qualifications for the job.

The main contractors are responsible for ensuring that those with the right qualifications install the system.  

TypeC – Drained cavity construction

Type C has become one of the most popular forms of moisture management among industry professionals. It is suitable for existing and new builds, is quick to install, and provides greater scope for dealing with errors.

This approach provides some initial protection against water and then uses a cavity drain membrane approach to remove any moisture that gets through. 

The water is then removed from the basement via a series of drains in a mechanical pump system. The external wall must be protected, as the system could become overwhelmed, resulting in dampness.

Maintenance of this approach is vital. The pump systems should be checked on installation and again after three months. After that, annual checks should ensure everything works, and any sediment build-up can be managed.  This approach is not ideal for some buildings with exaggerated design features

two workmen mixing concrete for basement waterproofing

Basement Waterproofing DIY

While these are the three approaches professionals can take to prevent and resolve any damp issues underground, there are a few things that you can do to avoid dampness becoming a problem. 

Manage surrounding areas

Ensure the area around your basement is as well managed as possible. For instance, ensure all downpipes are operational and proper drainage is installed around your property, particularly in areas prone to pooling water. You can also regrade the soil around the building so it slopes away from the house. 

Insulating Pipes

To avoid the effects of condensation, you can insulate cold pipes in the basement with insulation sleeves.

Ventilation Improvements

You can install fans or dehumidifiers to control the humidity in your basement, again helping to reduce the impact of condensation.

Install Window Well Covers

Adding or replacing window well covers is a relatively easy fix that can reduce water pooling and the potential for water to enter through the windows

Introduction of Heat

The introduction of heat during the winter will help to control the internal environment.

Choosing the right professional

While there are things you can do to protect your basement from dampness, it is vital to get a professional opinion to prevent the problem from worsening. 

However, finding the right professional is not easy. So here are a few pointers. 

They should be CSSW-qualified, and the work carried out should be up to BS 8102:2022 standards. They should have case studies and testimonials from previous clients to show you. 

If you are unsure, many in the UK will be registered with a trade body such as the Property Care Association, so it is worth checking them out there. And finally, their work should be guaranteed, but confirm this with them before they start.

Spend the time before you start your conversion making sure you know your options and enjoy the addition below your property for many years to come. 

Author – Dean Webster, Owner and Lead Surveyor of South East Timber and Damp

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