Challenge

To fulfil the requirements of BS 8102:2022 and BS 8485:2015+A1:2019 a strategy to develop a specification which combined structural waterproofing and ground gas protection was required for this refurbishment project.

The project involved creating additional living space to an existing mid-terrace Victorian property in London W12. The site of the property, whilst not being located on contaminated land identified as being potentially at risk, was near what is classed as contaminated land (an old brick yard).

To satisfy Building Control requirements gas protection measures were required to meet BS 8485:2015 and A1:2019.

Site investigations at former brickworks and landfill sites are within expected UK guidelines for contamination. Ground investigations incorporate both soil sampling, ground gas and groundwater monitoring.

In accordance with Table 3 of BS 8485:2015 and A1:2019 a residential building is classed as a Type A building, creating a “high risk” requirement for ground gas protection. With the structure requiring a Grade 3 habitable environment attention was required to offer a system which meets all requirements.

Delta registered waterproofing installers, MGA Contracts, carried out the refurbishment which initially involved lowering and reinstating the basement slab before installation of a suitable ground gas protection system and waterproofing system.

Methodology

For this project a specialist waterproofing and ground gas protection system was required. Following initial site inspections, review of site investigation reports, structural drawings and details, along with considering the requirements of Building Control for gas protection measures, and the client's need to have a dry basement, a strategy was developed to address all issues.

Addressing initial water ingress issues, incorporating a combined system of ground gas protection and structural waterproofing. The structure had been constructed with limitations which would impact on the specification of approach. Both the ground gas protection system and waterproofing system required an interface which would satisfy both the known and unknown levels of ground gas. By using two forms of waterproofing, an initial (primary) and a secondary system, such as a Type C cavity drainage system.

The residential structure was also required to satisfy requirements within BS 8485:2015 and A1:2019.

The project was split into two phases:

Phase 1 – to stop active leaks within the primary waterproofing system and to install a primary ground gas protection system.

Phase 2 – to install a secondary waterproofing system and ground gas protection system, such as the Delta Type C AT 800 Cavity Drainage System.

Products used:

  • Delta AT 800
  • Koster 2 IN 1 Resin Injection System
  • Koster NB1
  • Liquid Gas Barrier (LGB)
  • Koster Blitz Powder
  • Koster KB Flex
  • Koster NB Elastic Grey
  • Koster Sewer & Shaft

Outcome

The property required a flexible waterproofing system to allow for movement whilst remaining watertight. This was achieved using Delta’s AT800 Type C cavity drainage membrane.

With ground gas protection in combination with structural waterproofing, the most effective designs combine multiple forms of protection.

MGA Contracts Ltd has supplied the client with a dry, modern addition of living accommodation which will remain fully protected against the long-term threat of water and damp ingress and ground gas contamination that will also add value to the property.