Box window

Box windows have historically been used due to their comparatively good thermal insulation properties. Both the insulating layer of air between the window levels and the width of the box reduce heat transfer from the inside to the outside.

Box windows consist of two single windows with separate or shared frames connected by a lining. They also have excellent soundproofing properties due to the two window levels in front of each other.

The sound insulation level can be further increased by sound-absorbing inserts in the gap, appropriate joint sealing and differing glass thicknesses for the inner and outer windows.

Image: Box window - cut 58, proholz Austria, 2015

The assessed building sound insulation coefficient is a component-related parameter for airborne sound insulation and a characteristic parameter for sound insulation requirements according to VDI guideline 2719 or the DIN 4109 standard.

Both are divided into sound insulation classes I - VI.

Depending on the noise immission incurred, windows of the respective class are installed.

Basically,

• a reduction of 10 decibels is perceived by the human ear as halving the volume.
• With Class I windows, a sound insulation level of 25 to 29 dB can be achieved.
• Windows of the highest class VI, on the other hand, reduce external sound sources by more than 50 dB.
• Highly soundproofing systems such as those of class VI are usually implemented as box windows.

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