1 November 2013

Hard-to-treat cavities guidance

ofgem-logo-200dpiThe energy regulator Ofgem have yesterday (31st October 2013) published guidance on how industry should verify what constitutes a ‘hard-to-treat’ cavity wall. The guidance comes into effect on 1st January 2014, but in best practice terms the industry should apply the guidance as soon as possible.

This guidance is important because it relates to Energy Company Obligation funding and in particular to the biggest chunk of funding in monetary terms, the CERO (Carbon Emissions Reduction Obligation), although hard-to-treat cavities (HTTC’s) can be funded under all ECO headings.

The guidance covers three areas: narrow cavities, chartered surveyor reports and technical monitoring.

  1. Narrow cavities: this refers to cavities of 49mm or lower and the document provides a 6-page guide to how to measure this. A Narrow HTTC Declaration must be completed for all narrow cavities, so yet more paperwork.
  2. Chartered surveyor report: these are required for cavities that are ‘uneven stone’, or require remedial works or non-standard materials/techniques. The surveyor can complete this either through a site visit or as a “…desk-based exercise using a robust body of evidence.”
  3. Technical monitoring: 5 per cent of certain categories of HTTC will be subject to technical monitoring by energy companies at pre-installation or mid-installation stage, although narrow cavities can exceptionally be inspected post installation.

Surveyors are provided with clear guidance on how to verify the width of a narrow cavity, and should read pages 7 to 12 of the document. Essentially, three inspection holes per elevation are required at ground level and must be at least 500mm apart. The surveyor then calculates the mean cavity width for each elevation. It is important that a photograph or sketch records the location of each inspection hole.

Link to Ofgem PDF

Link to Ofgem ECO Guidance (160pp) PDF

Colin Anderson

  • insulation, regulation,


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