One important function of the building envelope is to protect the interior from unwanted outdoor noise. Sound insulation is an important parameter of building components, as outdoor noise can have negative effects on health, mood and learning capabilities.

4.1 Noise or sound

Human perception plays an important role in identifying whether it is noise or sound that we hear. Our ears are always listening and cannot be turned off. Our subconscious mind will constantly evaluate whether a sound is known or unknown, whether it is pleasant or annoying, or whether it represents a danger. If a danger is recognised, we will immediately be in an alert state and ready to run or defend.

Sound is defined as what you as a person can hear; noise is defined as unwanted sound, even at normal or low intensity levels.

It is important to have a good acoustic environment for the specific activity taking place, e.g. sleeping, watching TV, talking. What we describe as noise in one situation can be perceived as sound in another. Birdsong in the early hours of the morning, for example, can be perceived as noise and disturb sleep quality. Traffic in the city can have a negative influence and be evaluated as noise, but in other situations it can be perceived as sound; it can make you feel in contact with the surroundings and nature, and allow you to feel included in the community.

Noise can have a significant impact on the health and performance of building occupants. Stress, headache and learning difficulties can all be caused by noise. Sleeping problems and lack of rest can also be caused by noise (National Institute of Occupational Health in Denmark, 2006).

Scientists believe that noise can:

• Lower productivity
• Cause increased metal fatigue
• Trigger stress
• Result in extra sick leave.

It is known that noise can cause premature death. In 2003, it is believed to have been instrumental in the deaths of an estimated 200-500 people in Denmark (Danish Ministry of Environment, 2003).