2.1 Attenuation Incorporated into a Facade

One of the main difficulties in designing low energy buildings can be the prevention of noise break-in via vented facades. This chapter looks at a range of options and details which can be used to prevent environmental noise break-in from motorways, dual carriageways, trains, aeroplanes, inner city noise and other noise sources.

To overcome this issue an attenuator is selected and incorporated into the facade. This attenuator is typically combined with a damper such to control the flow of air into the building with a weather louvre being used externally to provide the weather protection. MACH Acoustics describes this combination of units as the ‘NAT Vent Box’. The outline schematic of this system is shown below. The damper can take the form of a thermal volume control damper, open-able vents within the facade, thermal insulated doors etc.

2.3 Locating Inlet Vents and Cross Vents as a Noise Control Measure

Locating Air Inlet Vents
The orientation of a building has a significant impact upon noise levels at the different facades of the building. It is often the case that facades on the opposite side of a building to a significant noise source will be considerably lower than those on the noisy side of the building.
By orientating the building and by placing non-critical spaces on the noisy side of a building, it is possible to form a good acoustic buffer. In these instances, cross vent can be used where the air intake is placed on the quiet side of the building. Cross ventilation to an atrium or circulation zone is then used to provide the air extract. Alternatively, single sided ventilation could be used for sensitive spaces on the quiet side of a building.
1 shows sound levels around a building in the form of a noise map. The classroom on the far side of building to the A40 are vented using openable windows.

1

Cross Vent to Assist with the Prevention of Noise Break-in
In instances where a building is located on an exceptionally noisy site, cross ventilation can improve the feasibility of natural ventilation. Cross ventilation has an important advantage over single sided ventilation, in that air inlet vents can be between 25% to 75% smaller than those required for single sided ventilation. This significant reduction in vent size helps considerably in preventing noise break-in, as smaller vents restrict the passage of sound into a building.