Building standards – guidance changes: letter to local authority verifiers - 11 July 2025

Dear Building Standards Managers and Energy Scheme Providers

Notification of change to content of the January 2025 Domestic Technical Handbook

To make you aware of a minor correction to the January 2025 Domestic Technical Handbook, which will be published shortly as v1.1 at Building standards technical handbook January 2025: domestic.

This relates to the compliance calculation undertaken using SAP 10.2 where a new dwelling is connected to a heat network. Note 6 to table 6.1 in guidance to standard 6.1 ‘energy demand’ is amended.

We have been made aware that SAP 10.2 applies the heat network distribution loss factor (DLF) to the calculated heating energy total for the dwelling as part of the calculation of the delivered energy total for the notional and actual building.

As the metric being reported on is delivered energy (that which is received at the dwelling boundary), this is incorrect and does not report this metric as intended. A distribution loss factor other than 1.0 will increase the energy total calculated. This means that a higher delivered energy total is reported and that the impact of other aspects of building specification will be proportionately less as a result.

We have agreed with BRE that the most effective solution is to set the DLF to 1.0 when undertaking a calculation to demonstrate compliance with standard 6.1 ‘energy demand’. Instruction on implementing this will be provided to software provides a part of the next planned notification under SAP 10.2.

The immediate action to rectify this, prior to correction in software tools, is as follows:

• Applicants should only input a DLF of 1.0 within the SAP 10.2 calculation submitted as part of the building warrant application.
• Where a verifier receives a calculation which notes a DLF other than 1.0, a revised calculation with a DLF of 1.0 should be requested prior to further checking of 6.1 compliance.
• This information is reported within the Heat Network section of both the SAP 10.2 ‘summary for input data’ as ‘distribution loss value’ and ‘full SAP calculation printout’ section 9b as ‘distribution loss factor’.
• Guidance note 6 to table 6.1 in the updated Domestic Technical Handbook (v1.1) is updated to reflect this process, noting ”for the purpose of the compliance calculation at design stage, the distribution loss factor for the heat network must be set at 1.0 to correctly report the heat component of the delivered energy calculation without factors or adjustment”.

This process should be applied to any building warrant applications yet to receive building warrant approval and to any applications received from this point onward.

It is not intended to apply this correction retrospectively. Applications which have already been determined under the current (post-February 2023) standards and a building warrant issued require no action on the part of the verifier. These may remain as approved and any amendment to such a warrant, which affects compliance with standard 6.1, but does not seek to increase the number of dwellings approved, may be processed on the same basis as the original building warrant.

We will write to you again once updates are made to approved SAP 10.2 software tools.

If you have any queries arising from this change, please contact us via buildingstandards@gov.scot.

Regards

Steven Scott
Head of Techncial Unit