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CIBSE and LETI submit joint response to National Calculation Methodology (NCM) Call for Evidence
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CIBSE and LETI submit joint response to National Calculation Methodology (NCM) Call for Evidence

25 Nov 22

In order to collate the most information possible in this short space of time, and in a single location making it more straightforward for the BRE and DLUHC to analyse, CIBSE and LETI have worked together to provide this joint submission. A large number of companies have provided support to this submission, through their expertise and modelling, including Buro Happold, Elementa, Etude, Hawkins Brown, Inkling, and Max Fordham.

We have previously noted that the NCM call for evidence did not receive much publicity, which combined with the lack of a deadline did not encourage submissions. Once a deadline was published, it was relatively short (2 weeks).

This response, therefore, focuses on essential points, including 3.4 Space Heating, but stresses that more comments and more evidence could be gathered given proper time.

This is just a snapshot of issues and evidence. CIBSE and LETI strongly recommend a comprehensive review of the NCM, starting with a scoping study in a similar fashion as was carried out for the Standard Assessment Procedure 11 (SAP11), to ensure NCM is suitable for the Future Buildings Standard and for future versions of Part L applied to work on existing buildings.

Download the full response 

The submission identifies the relatively short amount of time given to respond, highlighting that to comment meaningfully on all of the assumptions within the NCM, including occupancy density and profiles; assumed heating gains; and set points, for all building uses, would require significantly more time and should receive dedicated attention through a systemic study. 

NCM in context: Part L

While we understand that NCM is the calculation methodology, and is to some extent
independent from its context, in order to effective energy and carbon savings it needs to operate within a supportive ecosystem of regulations. Both CIBSE and LETI have expanded on this previously, and we would be very happy to have the opportunity to discuss this in more detail. In summary:
- The notional building approach needs to be reviewed, as it hinders comparisons
between building design options and over time, and does not drive absolute
improvements. It is very difficult for policy-makers, clients and designers to actually compare design options.
- Regulations on commissioning should be enforced. Ways to incentivise this through the Part L assessment should be investigated e.g. penalty on building systems efficiency used in as-built Part L calculations unless evidence is provided that commissioning has been carried out.
- The ADL2A requirement for energy forecasting should be meaningful i.e. through
performance modelling such as TM54, NABERS or PHPP. Current options such as
“benchmarks” and “design calculations” can mean all sorts of things. They may be of
very little use, or even misleading, to building occupiers.
- A significant measure to reduce the performance gap would be to require monitoring
and disclosure of in-use energy performance. There was a previous government
working group on proposals to introduce such a measure beyond public buildings. This
workstream needs to be re-invigorated, and the policy should be finalised and

Read the full response

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