Basement tanking is an investment for any homeowner, property developer, architect or specifier who is tackling an existing basement conversion or persistent water ingress. In any below-ground construction scenario where the structure is expected to be useful and/or habitable, effective waterproofing is essential to safeguard structures, belongings and long-term property value.

But how much does basement tanking cost, and what factors influence the overall price? This guide provides a detailed breakdown of the key factors and expert advice to help guide your decision-making process.

What Is Basement Tanking?
Basement Tanking, or internal Type A waterproofing, is just one of the methods of protecting a basement against water.

Basement tanking is the term that is commonly used when referring to a form of internal ‘Type A’ waterproofing, defined by British Standard 8102:2022 as “barrier waterproofing”.

Barrier waterproofing products that can be applied to the internal surface (also known as the ‘negative’ side) of the structure include a variety of cement-based liquid-applied slurries or renders. These products are installed directly onto the prepared internal wall surface, where they must actively hold back any ingressing water. It is therefore crucial to select the correct product and to ensure that the substrate is prepared correctly.

Whilst tanking is a popular solution for both new build projects and cellar conversions, another method of basement waterproofing that can provide enhanced protection is the cavity drain waterproofing system, otherwise known as ‘Type C’ waterproofing.

Combined Waterproofing for Enhanced Protection
British Standard 8102:2022 defines Type C waterproofing as “drained protection”. This involves accepting the leaking water into voids created by the cavity drain system that are strategically installed to the internal walls and floors of the structure. As a result, the system captures and depressurises incoming water before safely removing it from the property.

Unlike Type A waterproofing, Type C waterproofing does not resist water pressure, therefore avoiding common problems such as installation issues, preparation issues, and impact damage, which can affect Type A barriers and allow water to enter the structure.

Overall, basement tanking can deliver a robust barrier against moisture and water, transforming basements into dry, usable spaces. However, if you are looking to create a habitable below-ground space it is recommended that the tanking system is combined with a Type C system to provide multiple forms of protection and comply with the recommendations within BS 8102:2022. The standard recommends that combined systems should be considered if the assessed risks are deemed to be high or the consequences of failure to achieve the required internal environment are deemed too high.

Understanding Basement Tanking Costs in the UK
Basement tanking costs in the UK can vary significantly, with many variables and factors that can affect the pricing. It is therefore extremely difficult to provide a guideline cost for basement tanking without knowing more about the specific details of individual projects.

Some of the factors that can influence the cost of a basement tanking project include the size and complexity of the basement area, the desired end-use of the space, the chosen waterproofing method/s, the condition and age of the building structure, the level of risk from water and/or ground gases, and even regional labour costs.

Here’s a more detailed look at some of the key factors affecting basement tanking costs.

Key Factors Affecting Basement Tanking Costs
Several factors contribute to the overall cost of basement tanking and waterproofing:

Size of the Basement: Perhaps the most obvious one, as larger basement spaces naturally require more materials and labour, increasing the total price.

Purpose of the Basement: Quite simply, what will it be used for? For example, is it going to be a plant room where damp is tolerable, ventilation won’t be necessary, and just one type of waterproofing would suffice? Or is it going to be a home cinema, a gym or a bedroom, requiring a completely dry internal area, multiple forms of waterproofing to deliver robust protection, and mechanical ventilation systems?

Waterproofing Method: Type A tanking products are often more cost-effective per square metre than Type C cavity drain membrane systems. However, the cost of preparation to ensure the waterproofing has the required bond to the substrate can be very high. Cavity drain waterproofing is generally considered the safest form of waterproofing, and is often recommended alongside the tanking system in situations where a habitable below-ground area is required.

Type of Structure: Is it a basement conversion or extension? Is it underpinned, is it a new or an existing structure? Is it built from reinforced concrete or brickwork? Is it a listed/historic property or a new build? All these factors and more will heavily influence the type of products that can be specified and installed to deliver your waterproofing system.

Condition of the Basement: Correctly applied basement tanking systems require thorough preparation before they are installed. If your basement has existing problems that first need to be rectified, such as live water leaks or structural repairs, then this will add to the total price.

Location: Is the structure built in the side of a hill with little risk from rising water tables and the ability to drain water away from the property using gravity? Or is it built to a low-lying area in a city, with risks from ground and surface water and burst water mains? Higher risk locations may require more comprehensive systems.

Labour Costs: Depending on geographical location, labour costs can vary significantly. For projects in London and the South East labour costs tend to be higher, with regional variations of up to 20%.

Complexity: Awkward shapes, vaulted ceilings, or difficult access can add complexity and time to the installation process, therefore increasing labour costs.

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