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Noise - EnvironmentalHome Insulation - Windows

Improving Windows/Glazing

As with ceiling and wall treatments, the basis of good sound insulation is increasing mass, structural isolation and effective sealing. The directory can be consulted for details of suitable glazing systems.

If not replacing but upgrading existing glazing -

  • Make good any gaps or cracks in the existing glazing, including edge sealing.
  • Secondary glazing can be installed behind the existing glazing; effectiveness is a trade off between the size of the gap and the thickness of the secondary glass and of the original glass; probably the new glass panes should be 8mm or thicker, and ideally of a different thickness to the existing glass
  • The new inner pane should be set into a separate heavy well sealed frame;
  • The air gap between the two frames should ideally be at least 100 mm, but above say 150 mm you are in the region of diminishing returns where a large increase in air gap is required to make a significant change in the insulation.
  • The side and top reveals should be fitted with acoustic tiles to reduce reverberation inside the units; don't be tempted to put acoustic tiles on the window sill because any condensation on the windows will run down and be held within the bottom tiles and rot! This may lead to bad smells.

If new glazing is being installed

  • Be wary of installing true sash windows, if acoustic performance is important; the sash mechanism makes it difficult to achieve a good seal, in addition it is difficult to use heavy glass because of the weight on the sashes.
  • If the noise source lies off to one side of the window, arrange for side hung casements, with the hinges closest to the noise source; that way, the open side of the window will screen the room from the noise; if the opening light was on the other side it would tend to catch and deflect noise into the room; the difference between "screening" and "catching" can be 10 dBA. The window should be set well into the windows opening, so that when open, the gap between the open light and the frame would be set into the opening.
  • The glazing can be a repetition of the secondary glazing systems above, or a compromise entailing lower cost, space and performance, would be
    • 10mm glass, a 12mm air gap in the same frame and a 6mm inner glass
    • or 6.4mm laminated glass, 12mm air gap and 10mm glass; consult the directory for details of laminated glass suppliers.

Ventilation for new or upgraded glazing

Clearly, the performance of windows is better when they are kept shut!. Silenced mechanical ventilation may be installed such that there is no requirement to open the windows for ventilation; thereby reducing sound insulation. The directory can be consulted for suppliers.  Alternatively there are silenced passive ventilations which can be fitted over the frame.

Another alternative to mechanical ventilation would be arranging for opposite sections of the inner and outer glazing to be openable; thereby permitting ventilation through the staggered opening whilst preventing a direct sound path. As a comparison,

  • closed secondary glazing can reduce traffic noise by around 35 dBA,
  • open glazing (single or secondary) can reduce traffic noise by around 15 dBA,
  • secondary glazing with "staggered" openings can reduce traffic noise by around 25 dBA.

A 10 dBA difference is generally regarded as a halving or doubling of noise level; therefore closed secondary glazing is twice as good as "staggered opening", which itself is twice as good as open glazing of any form.

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