4.5 Evaluation and measurements

4.5.1 General aspects

The most effective way of reducing the noise is by the reducing the “source” – e.g. reduce traffic noise by reducing the number of cars, prohibiting trucks, imposing speed limits or installing noise barriers close to the road. If this is not possible, the building envelope's ability to reduce the noise level has to be evaluated/calculated (see principle below) so as to obtain acceptable noise levels for the occupants (SBI, 2014a).

4.5.2 Sound insulation

Individual building components, and joints between components, contribute to the overall sound insulation of the building envelope.

The consequence is that a building envelope that fulfils a certain sound insulation level can consist of various building components with lower and higher sound insulation, but together they will reach the required level.
​Figure 4.5.1 Main principle of process by calculations of indoor traffic noise levels (Lden (inside)). The process is repeated if the requirements for the highest value of Lden​ (inside) have not been met. 

4.5.3 Measurement of sound insulation according to European standards

EN ISO 10140 series and EN ISO 717-1 (CEN 2010; CEN, 1997) apply to the testing and classification of the sound insulation of a window. The sound insulation found from the measurement is expressed as Rw(C, Ctr) in dB. The Rw value expresses the ability to reduce noise from outside to inside the building. Two correction factors (C and Ctr) are also found from the measurement.

The C factor should be used if the source of sound is speech, Ctr if the source of sound is rhythmic music or traffic noise.

A typical roof window with a standard construction of 2 layers of 4 mm glass, 16 mm cavity and 4 mm glass will attain an Rw of 32 dB.

If further sound insulation is needed, then windows with a pane construction of 2 layers with different glass thickness (4mm and 6 mm) will achieve a better sound insulation than a window with a standard glazing unit. Panes with 3 layer glass units with different distances between glass, and glass thickness, also perform better than the standard solution. Using a different gas filling will also have an effect – krypton gives better sound insulation. And finally, laminations are another way to achieve higher sound insulation of the glazing unit.


Roof window with a glazing unit of 4 mm glass, 16 mm cavity with argon, and 4 mm glass (4-16-4)

​Figure 4.5.2 Example of sound insulation of roof window with two glazing types. 
​Keep noise in bedroom low.
CEN (1997) EN ISO 717-1: Acoustics - Rating of sound insulation in buildings and of building elements - Part 1: Airborne sound insulation
CEN (2010) EN ISO 10140 serie: Acoustics - Measurement of sound insulation of building elements
Danish Building Research Institute (2014b) Lydisolering af bygninger teori og vurdering – SBI anvisning 245