The key requirements relevant to the use of hardcore material for buildings are set out in Part C (Site Preparation and Resistance to Moisture) and Part D (Materials and Workmanship) of the Second Schedule to the Building Regulations.
Part C (Site Preparation and Resistance to Moisture) of the Second Schedule to the Building Regulations sets out the legal requirements for Site Preparation and Resistance to Moisture. Requirement C4 stipulates that “the floors
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walls and roof of a building shall be so designed and constructed as to prevent the passage of moisture to the inside of the building or damage to the fabric of the building”.
Part D, Requirement D1 specifies that "All works to which these Regulations apply shall be carried out with proper materials and in a workmanlike manner”. Requirement D3 defines “Proper Materials” as “materials which are fit for the use for which they are intended and for the conditions in which they are to be used”.
The related Technical Guidance Documents — TGD C and TGD D provide guidance on how compliance with the requirements of the Building Regulations can be achieved in practice. Work carried out in accordance with the guidance provided in the TGDs is considered prima facie evidence of compliance with the Building Regulations.
TGD C provides guidance on hardcore for use in buildings. It states that "hardcore should conform with IS EN 13242:2002” (Aggregates for unbound and hydraulically bound materials for use in civil engineering work and road construction) “and meet the specification as outlined in Annex E of the accompanying guidance document to this standard, SR21:2004+A1:2007”.
Standard Recommendation (SR) 21:2004+A1:2007 provides specific guidance on reducing the risk of reactive forms of pyrite being present in material fill for use under concrete floors in dwellings and buildings. Annex E in SR 21:2004+A1:2007 is an example specification for unbound granular fill for use under concrete floors and footpaths and limits the total sulphur content to 1%.
The onus is on the builder/developer to ensure that all works undertaken are compliant with the relevant parts of the Building Regulations.
In the High Court case referred to in the question, it was acknowledged that Clause 804 is, in fact, a material superior to what is usually needed for construction infill and underfloor support. It is manufactured and sold on the basis that it is a high quality product. The quarry supplied stone fill which contained pyrite. The pyrite in the stone fill caused the heave in the subfloor area which caused the concrete ground floor to heave and crack.
This case is on appeal to the Supreme Court.
I will consider the necessity for any changes to the specification for hardcore on receipt of the report from the Pyrite Panel.