Standard Recommendation (SR) 21:2004+A1:2007 provides specific guidance on reducing the risk of reactive forms of pyrite being present in hardcore material for use under concrete floors in dwellings and buildings. It includes an example specification (Annex E) for unbound granular fill for use under concrete floors and paths and limits the total sulphur content to 1%. The example specification sets out verifiable performance criteria for hardcore. It sets the quality of the aggregate (attempting to rule out low quality stone), the grading (reducing the level of fines) and the results required from sulphur-related chemical tests. If the value of total sulphur content during initial testing is less than 0.1%, no further testing is required, unless there is a significant change in the quarry deposit. However, if the result is between 0.1 and 1%, there is a risk of swelling from pyrite, and it is advised that a suitably experienced petrographer carry out a detailed mineralogical examination to establish: (a) the material’s suitability as hardcore under floors and footpaths, and (b) an appropriate testing frequency for total sulphur based on the variability of the quarry deposit.
The Building Regulations set out the legal requirements for the design and construction of buildings, including houses and extensions. Technical Guidance Documents (TGDs) provides guidance on how compliance can be achieved in practice. TDG D (Materials and Workmanship) requires that all works are carried out with proper materials which are fit for the use for which they are intended. More specifically, TGD C (Site Preparation and Resistance to Moisture) requires that hardcore conform with I.S. EN 1342:2002 and meets the specification in Annex E of SR21. In this regard, the Pyrite Panel noted in its report that there are no reported instances of dwellings commenced after 2007 which became the subject of pyrite related claims to structural guarantee providers.
Responsibility for compliance with the requirements of the Building Regulations rests with the owner and /or the builder and the onus is on the builder to ensure that the infill material he is using meets the requirements set out Standard Recommendation (SR) 21. The recently published pyrite report contains a recommendation on the development of a standalone specification for hardcore which will require quarries to put in place robust testing and traceability procedures.