## 2 Natural Ventilation-Enabling Facade Noise Control Devices
### Fins, Lintels, Screens, and Similar Protrusions  
The protrusions on the facade of a building next to a noisy road act as sound barriers and protect the windows behind them. Figure 2 illustrates the various forms of these devices which have previously been proposed by a number of researchers. As it is possible to open the windows, natural ventilation can be achieved. For a single apparatus of protrusion, the acoustical insulation may be calculated using the reduction in the view angle of the road seen by the receiver (windows/openings), as suggested in CRTN [23]. However, for a vertical fin, the protection will be largely limited because of the reflection by this fin, unless appropriate sound absorption is installed. When a window is located between two vertical fins, this situation is even worse, because of the multiple reflections between the fins. [PERSON] et al. [24] numerically illustrated the noise distribution within a vertical re-entrant region of a high-rise building facing a parallel road. The channel-like dual-fin structure resembles a re-entrant region, which tends to direct the noise energy to the upper floors. The maximum traffic noise protection which can be offered by a vertical fin, even with sound absorption, is believed to be less than 3 dB. Lintels installed on building facades are horizontal canopies, as well as sound barriers when noise sources are located below them. Thus, they can theoretically help screen traffic noise. [PERSON] et al. [25] numerically studied the sound attenuation achieved by the installation of thin rigid horizontal screens  
Figure 1: Examples of normalized traffic noise spectra. \(\blacklozenge\) EN1793-3 [21]; \(\blacklozenge\): [PERSON] et al. [22]; \(\blacksquare\): in-situ measurement 1; \(\blacktriangle\): in-situ measurement 2. Figure 2: Examples of protrusive devices (excluding balconies). (**a**) Lintels; (**b**) vertical fins; (**c**) eaves; (**d**) eaves with louvers. on building facades. The effect of the shapes of these screens on the acoustical protection was also examined. It was found that a circumference-arc-shaped screen performed better than a straight inclined screen, in terms of the acoustical protection, provided that the locations of the edges were unchanged. However, the screens were not found to be useful at the lower floors of a high-rise building, where the reflection from the screen of the immediate upper floor was significant enough to erase the sound barrier effect of the lower screen. Therefore, sound absorption needs to be installed on the reflecting surfaces of the screens [26]. However, these screens are not effective noise control devices when compared to balconies [27] (discussed later). Eaves and louvers on the facade of a building can help reduce solar heat gain by providing shade. [PERSON] et al. [28] investigated the acoustical protection of different types of eaves and louvers, using scale model experiments. Similar to the results of the screens discussed above, the horizontal eaves/louvers did not provide meaningful acoustical protection, unless the sound incidence angle was large. Vertical louvers behaved in a similar way to vertical fins, and were less effective than the horizontal ones. Sound absorption was required in order to improve the overall acoustical performance (corresponding sound absorption coefficients were not provided). [PERSON] et al. [28] showed that the insertion losses of eaves, louvers, and their combinations, ranged from 1 to 10 dB. However, the sound incidence angle has to be as large as 80\({}^{\circ}\) for the insertion loss to be higher than 4 dB. [PERSON] et al. [29] showed that the installation of sound absorption (7 mm thick polyurethane conglomerate of density 70 kg/m\({}^{3}\)) onto the solar shading louvers, could help reduce the noise level by \(\sim\)5 to 6 dB in the high frequency range (1.6 kHz to 5 kHz), when compared to those without absorption, for the case of a commercial building.