The existing background noise level should not include existing plant associated with the assessed building (criterion 2.a.i). Both existing and newly specified externally mounted plant should be considered within the noise impact assessment as part of the ‘rating noise level’ (criterion 2.a.ii).
However, for Part 2 only and Part 3 only assessments, as indicated in the relevant CNs within the manual, only the noise impact of existing or new externally mounted plant specified within the scope of that Part is to be considered.
For example, in a Part 3 only assessment, where existing plant forms part of the core services and new plant is installed as part of the local services, only the impact of the noise generated by the new plant should be considered. The existing plant noise should be included as part of the existing background levels.
Issue Pol 05 assesses the impact of existing and newly specified externally mounted plant and the impact of any fabric measures on reducing the impact of noise on any nearby noise-sensitive buildings. Its applicability is relevant to all treated buildings where Part 1 is included, even where the existing plant is not being upgraded and is scope dependent when Part 2 or Part 3 only assessments are carried out.
13.08.18 KBCN content amended to include consideration of Part 2 or Part 3 only assessments. This will be clarified in the next manual re-issue.