4.4 Outdoor noise

4.4.2 Parameters affecting outdoor noise level

Location

The surroundings of a building have a major influence on the expected outdoor noise level. For example, the average outdoor noise level can be 60 dB(A) in a city centre and 50 dB(A) in a suburban residential area (ÖNORM, 2006).

The distance to the noise source has a decisive influence on the perceived sound level. Doubling the distance from the source reduces the sound level by approximately 3-6 dB. Unobstructed noise from a single source will be reduced more than noise from a linear source, such as traffic.

The presence of noise barriers, and reflections from and absorption in their surfaces, will affect the sound level at a specific location.

The source itself plays a role – traffic generates low frequency noise, birdsong high frequency noise.

Other factors that affect the sound level – and how it can be redirected – are a building opposite, trees (summer or winter appearance), and the geometry of the noise barrier and its surface absorption properties.

4.4.3 Traffic noise

Traffic noise increases stress levels and the risk of cardiovascular diseases. A conservative estimate is that between 200 and 500 people in Denmark are dying prematurely from cardiovascular diseases and hypertension every year in Denmark because of traffic noise (Miljøstyrelsen, 2010).

In the first example shown below, a roof window experiences 8 dB lower noise levels than a facade window in the same building. For a roof window facing the back yard, that figure even falls to app-roximately 15 dB lower noise levels.

The second example shows that an opposing building will reflect some of the noise and reduce the diminution in noise level experienced by the roof window by 5 dB (ÖNORM, 2006).

​Figure 4.4.1 The examples show that facade windows experience higher outdoor noise levels than roof windows situated in the roof.

​Figure 4.4.2 Illustration of noise levels in a city. 

4.4.4 Rain noise

The sound/noise of rain on the roof is perceived differently. For some it is a pleasant sound, for others it is noise. At night, most will perceive it as noise if they are woken up by it.

To enable comparison of different products, the international test standard EN ISO 140-18 (CEN, 2006) has been developed to measure rainfall sound pressure levels.

Furthermore, French authorities have made requirements limiting the rainfall indoor sound pressure level to SPLmax<50 dB so children will not be woken up by the sound of rain (Ministère De La Santé, 2005).

The VELUX Group has developed the first roof window that can reduce rain noise. With a sound pressure level of 48 dB, it fulfils the French authorities’ recommendation of a rainfall sound pressure level of max. 50 dB indoors.

4.4.5 Heavy noise
(aircraft, trains, trucks)

Aircraft, trains and trucks generate very high noise levels (aircraft engines emit more than 110 dB), often in the low frequency area, which are difficult to reduce.

13% of the population of Europe is highly disturbed by the noise of road traffic, 5% by air traffic and 3% by railways (WHO, 2009).

Due to the high-energy noise and its low frequency range, noise distribution and noise reduction solutions must be calculated by specialists.

​VELUX roof window with rain noise reduction.