Energy Companies Obligation (ECO): Consultation on requirements for demonstrating characteristics of hard-to-treat cavities

Publication date
27th August 2013
Closing date
24th September 2013
Policy areas


On 27 August 2013 we published a consultation document seeking views on our proposed requirements under the Energy Companies Obligation (ECO) for demonstrating the characteristics of a hard-to-treat cavity wall (HTTC) to which insulation has been installed.

The consultation put forward proposals to address concerns that a significant number of HTTC measures installed under ECO may have been installed to cavity walls that do not meet the statutory definition of ‘hard to treat cavity’. The consultation closed at 1pm on 24 September 2013.

Response to consultation

Responses were received from six energy suppliers and 47 other stakeholders. The responses are published below.

We have taken on board many of the comments and suggestions made in these responses and have revised our original proposals for demonstrating the characteristics of HTTCs accordingly. We believe that this will significantly reduce the cost and resource impact of the new requirements, which are far lower than the cost of potentially incorrect measures that consumers would otherwise bear (based on our reviews of the measures initially submitted to us).

We have published a document summarising the issues and suggestions raised in the response to this consultation. In this document, we explain the changes we have made to our proposals as a result of the consultation and detail where we were unable to incorporate suggestions made by respondents. Some responses raised issues relating to the overall policy design of ECO. We have passed these comments on to the Department of Energy and Climate Change (DECC) for their consideration as they are responsible for ECO policy and legislation.

Outcome of consultation

As a result of this consultation we have published the Energy Companies Obligation (ECO): Supplementary guidance on hard-to-treat cavity wall insulation, which can be found on our website .

The main requirements introduced by this supplementary guidance are outlined below.

Narrow cavities

A Narrow HTTC Declaration (Appendix 1, or an approved equivalent) must be completed for all narrow HTTCs.  The declaration must show that:

  • The cavity width has been measured in accordance with the methodology in Chapter 2; and
  • The measurement of the cavity width and the completion of the declaration has been conducted in accordance with one of the options in Chapter 2.

Chartered surveyor report for HTTCs

All HTTC measures notified to Ofgem as remedial works, non-standard materials or techniques, or uneven stone, must be identified as such in a report by a chartered surveyor, using the template provided in Appendix 2 or an approved equivalent.

Chartered surveyor reports must be completed either through a site visit or through a desk-based exercise using a robust body of evidence. In a minimum of 20 percent of cases the report should be based on a site visit undertaken by the chartered surveyor.

Technical Monitoring

An additional 5 percent technical monitoring will apply to the following categories of HTTCs:

• narrow cavities;
• cavities requiring substantial remedial works;
• cavities requiring non-standard materials or techniques.

This technical monitoring should be conducted at the pre-installation or mid-installation stage. As an exception, for narrow cavities only, suppliers may choose to conduct a proportion of the additional technical monitoring at post-installation stage; this must include measurement of the cavity width.

Date of effect

The requirements in this document take effect for installations completed from 1 January 2014.


The templates for the Narrow HTTC Declaration and the Chartered surveyor report for hard-to-treat cavity measures have been updated. The new version of each document was published on 31 October 2013 with the Supplementary guidance on hard-to-treat cavity wall insulation.

Any questions regarding the consultation can be emailed to

Response documents