Crushed Stone for Under Foundations

Bennettsbridge Limestone is NSAI certified to manufacture and supply all SR21 Annex E stone products for use under concrete floors and footpaths

The National Building Regulation’s Technical Guidance Document (TGD) C – “Site Preparation and Resistance to Moisture,” states that hardcore for use under concrete floors and footpaths must comply with S.R. 21 Annex E.

To be certified to manufacture and supply S.R. 21 Annex E products, Bennettsbridge Limestone is audited annually by the NSAI for certification of compliance of our Factory Production Controls (FPC) as outlined in I.S. EN 13242:2002.

Certification to manufacture and supply S.R.21 Annex E product requires and annual examination of our quarry by a Professional Geologist and extensive chemical, geometrical and physical testing.

S.R.21 Annex E specifies four products for use under concrete floors and footpaths:

  • S.R.21 Annex E – T0 STRUC
  • S.R.21 Annex E – T1 STRUC
  • S.R.21 Annex E – T2 PERM
  • S.R.21 Annex E -T3 BLIND


SR 21 Annex E – Product Outlines

May be used up to a level not closer than 900mm below the radon barrier/DPM. Thereafter, ‘T1 Struc’ and/or ‘T2 Perm’ is used to make up the 900mm to the radon barrier/DPM.
Can be used beneath blinding layer where a gas permeable layer (T2 Perm) is not required or can be used under 200mm of ‘T2 Perm’ to any depth.
This is a gas permeable material and must be used beneath the blinding layer and wherever a radon sump is present. The layer must not be less than 200mm in depth. For residential loading, ‘T2 Perm’ may be used as the sole fill material up to a maximum depth of 900mm or ‘T1 Struc’ may be used beneath it
Used in all cases to blind off the top layer of the hardcore and so is used immediately below the radon barrier/ DPM, to mitigate the risk of puncture.

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