Out of sight, out of mind? Protect below-ground structures from the power of water

Reflecting the continued growth in demand for below-ground structures in general, and residential basements in particular, a renowned British Standard has just been comprehensively revised. This blog post confirms what’s covered, and what’s changed. 

Did you realize that for economic reasons it’s become vitally important that below ground structures are well-constructed? This is because of the cost when they go wrong. We all know that as house prices have risen, homeowners, particularly in high density parts of the country, are using the building of basements as an affordable way to extend their home. But it’s at a price.

Research by Direct Line Insurance showed a 9 per cent increase in planning applications for basement builds between 2013 and 2015. Three-quarters of these are in London where ground water and hidden underground streams present complications. One consequence is that the National House Building Council (NHBC) for example, paid out £21 million in claims due to leaky substructures between 2005 and 2013 – affecting almost 900 homes.

It suggests that those responsible for the construction of waterproof basements could benefit from some authoritative and up-to-date guidance. Which is where the new BS 8102:2022 Code of practice for protection of below ground structures against water ingress comes in.

Preventing water from getting into buildings

BS 8102:2022 gives recommendations and guidance on dealing with and preventing surrounding ground water from entering into a structure below ground level. It covers the three main methods of waterproofing below ground structures, which are waterproofing barrier materials applied to the structure; structurally integral watertight construction; and drained cavity construction.

The document also covers the evaluation of groundwater conditions, risk assessment and options for drainage outside the structure. It applies to structures that extend below ground level and those on sloping sites. It covers the needs of both shallow structures – those of one storey below ground level – and deep structures, of more than one storey below ground level.

Expanded scope

The 2022 revision of BS 8102 updates a well-known and widely adopted standard that’s used both in the UK and beyond. To maintain it’s popularity, the content has been comprehensively revised so that it continues to reflect the latest developments and materials used in below-ground structures.

To that end, BS 8102:2022 has an expanded scope which now includes buried roofs and podium decks: two increasingly popular structures, but ones that bring their own challenges in terms of waterproofing.

As well, this time around, the editors have further clarified when this standard applies. They’ve also improved the coverage of other below ground infrastructure, such as tunnels, as this was felt to be inadequately covered in the 2009 version.

In addition, this revision now reflects wider developments in the sector. It includes new guidance on the need for experienced competent contractors for waterproofing installations, following the example set by other British Standards such as BS 8485 on the design of protective measures for methane and carbon dioxide ground gases for new buildings.

This update also takes the opportunity to include new guidance on how to comply with fire regulations for multi-storey underground structures. It also clarifies the grades of waterproofing protection.

Why use the revised standard?

BS 8102:2022 will remain an important document because it’s comprehensive and authoritative, benefiting as it does from the input of a wide range of experts. They include representatives from among others, the Institute of Structural Engineers, the Royal Institute of Chartered Surveyors, the National Housebuilding Council, the Property Care Association and the Construction Industry Training Board.

As a result, we have a standard that will continue to be seen as the leading document in this discipline. It will also enable users to develop their expertise and get the most out of the designs and materials chosen to prevent water ingress. And it will continue to reassure clients and end users alike that a given structure has been built using best practice and can be trusted to be waterproof.