## 3 Acoustic Design Criteria for Naturally Untilated Residential Buildings
The draft Acoustics Ventilation and Overheating Residential Design Guide (hereinafter AVO guide), produced by the Association of Noise Consultants in the UK, allows for higher levels of indoor noise from transportation sources when higher ventilation rates are needed to mitigate overheating, for example, by window opening, based on the following assumptions: (i) overheating occurs only for short periods of the year, (ii) suboptimal acoustic conditions are bearable when counterbalanced by better indoor thermal and air quality conditions, and (iii) occupants are provided with some control over their environment [79; 81]. However, as stressed by the AVO guide, this proposal is not supported by available research on human response to combined heat and noise. The AVO guide constitutes a proposal of an integrated framework to assess acoustic, ventilation, and overheating, in order to overcome the current incompatibility of assumptions between acoustic and mechanical designers. In fact, while the former considers windows being closed to control external sound access, the latter assumes windows being open for ventilation and overheating mitigation purposes. Thus, building occupants are eventually forced to choose whether to satisfy their acoustic or thermal and ventilation needs, without giving them the possibility of living in fully healthy and comfortable environments. In addition to standards and design guidelines, a series of international building rating and certification systems has been reviewed. Building assessment protocols typically provide design criteria to be met in order to gain credits that, summed up, constitute the score reached by the building which corresponds to a certain certification level. Background noise level limits guiding the credit assignation are provided in Table 3, together with sound sources to be considered, measurement conditions, and allowed tolerances. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Background Noise Level Limits** & **Sound Sources Considered** & **Measurement Conditions** & **Tolessances** \\ \hline BREEM International New & No limit for residential buildings & - & - & - \\ Construction [52] & & & & \\ \hline \multirow{4}{*}{Green Star—Design \& a built} & Mechanically ventilated and mixed mode buildings internal ambient noise levels in residential buildings rooms and bedrooms are no more than 5 dB (A) above the lower limit in the range & Indoor and outdoor sources & In NV buildings all measurements must be & - \\  & recommended by standard AS/NS2/2017-2018 buildings: the & (building service systems, traffic sources, industrial plants) & performed with NV openings in the open position. & \\  & above the lower limit in the range recommended by standard & & & \\ \hline \multirow{4}{*}{Home Quality Mark ONE [84]} & \multirow{4}{*}{L\({}_{\text{Log}}\)\({}^{2}\): 35 dB for hauline rooms and skinchers, L\({}_{\text{Log}}\)\({}^{3}\): 35 dB (default)} & Indoor and outdoor sources, with building service systems on & Internal noise level measured with cloud windows and open & 3 dB allowed for an individual room \\  & & (night: 230-07-00) & (contractor in noise in the measurements for tick  
Building rating systems generally provide reference values for indoor noise levels in residential buildings and such levels are typically derived from acoustic criteria for mechanical services. Noise limits refer to either (i) overall indoor noise or (ii) noise exclusively produced by HVAC systems [85; 86]. In detail, more relaxed limits for naturally ventilated buildings are only included in the Green Star protocol [83]. Differently, the BREEAM protocol regulates indoor noise exposure indirectly through limits on airborne and impact sound insulation [82], thus, not referring to the ventilation strategy. Measurements must be performed with window opening positions according to building operating conditions [83; 87; 88] or with closed windows and open trickle vents, if required for the ventilation strategy [84].