by Jack Harvie-Clark, 19th December 2019.
Disclaimer: These notes are my opinion only, not those of the Association of Noise Consultants’ committee that wrote the AVO Guide. As opinion, no liability is accepted for any errors or omissions.
What is the AVO Guide and why has it been produced?
The AVO Guide outlines an approach to acoustic assessments for new residential development that takes account of the interdependence of provisions for acoustics, ventilation and overheating. Noise and ventilation, and noise and overheating are addressed separately, and with different noise guideline criteria. Previous guidance is not clear about the acoustic implications of different ventilation strategies. Previously, there has been no guidance at all for assessing acoustic conditions when opening windows are used to mitigate overheating. This issue has hitherto been ignored, with noise assessments requiring that windows remain closed to achieve reasonable internal noise levels, while overheating assessments simultaneously assume that windows are open to mitigate overheating. The AVO Guide is internationally ground-breaking in proposing this integrated approach. We are majors authors of this new guide; you can read our previous and ongoing research on the assessment of noise, ventilation and overheating here. The AVO Guide methodologies for assessing noise & ventilation and noise & overheating are summarised below.
Assessing noise & overheating
- The AVO Guide proposes a two-stage assessment approach for noise & overheating. The Level 1 site risk assessment assumes use of a partially open window to mitigate overheating. Example external noise levels for each risk category and suggested actions are shown in Table 2. Note these categories of values are not shown in the AVO Guide, but may be derived from the information therein.
- Level 2 assessment takes into account how frequently and for what duration the overheating condition occurs – based on the principle that higher internal noise levels may be acceptable if only necessary for a shorter duration. This approach is intended to enable the use of open windows1 rather than relying on energy intensive mechanical cooling systems. A Level 2 AVO Guide assessment is recommended if the Level 1 assessment outcome is “Medium” or “High”.
1Other benefits of opening windows are discussed here.
2The external noise levels above assume a steady road traffic source and may differ for other types of transport. When evaluating the potential for adverse effect, all three aspects of noise exposure (i.e. daytime, night-time and individual noise events) should be evaluated.
3The basis for the AVO Guide criteria for individual noise events, LAF,max is described in our IOA paper.
Assessing noise & ventilation
- Internal noise levels should achieve the criteria in Table 4 of BS 8233 when providing adequate ventilation for internal air quality as defined in Approved Document F (AD-F) for whole dwelling ventilation.
- Table 2 illustrates the extent of external noise levels that may be feasibility with “typical” or “acoustic” elements for glazing and trickle vents, for each AD-F System.
- Mechanical services used for ventilation should meet suitable noise limits; example criteria are proposed in the AVO Guide. Find out more about the issue of noise and ventilation in dwellings here.
- No specific acoustic criteria are necessary when using purge ventilation for the purpose of rapidly diluting indoor pollutants, such as when painting or after burning toast.
To use this table: identify the daytime and night time LAeq, T levels, and the LAF,max for the ventilation design case. The value furthest to the left hand side is likely to represent the most significant constraint. For the constraining noise level, observe if there are likely to be acoustic constraints for different ventilation strategies. This table helps to quickly identify which ventilation strategies may be feasible, but does not replace the need for detailed calculations. specific to the case in hand.
1Changes to AD-F are currently under consultation. Significant changes are proposed to the AD-F ventilation systems such that the upper external noise levels presented above may no longer be applicable. Other ventilation systems may be possible, such as the attenuated passive ventilation options described here.
2The external noise levels above are based on a relatively worst-case scenario, which is described in Appendix B of the AVO Guide. Assessment results may differ depending on the actual room volumes and glazing areas proposed. Higher performance can be achieved with secondary glazing in very noisy environments.