Windows general:
Secondary glazing

The term refers to a second single-glazed glass 'window' that is fitted inside the room to the main (prime) window. These days secondary glazing is used mainly to achieve sound insulation although originally secondary glazing was fitted to original prime single glazed windows for heat insulation purposes. It may surprise you to know that the idea of double glazing and secondary glazing goes back many years: as far as I recall it was as long ago as the 1930s (someone correct me if I am mistaken) that double glazing was first really considered.

For secondary glazing to be at its most effective the gap between it and the prime window needs to be somewhere in the order of 50mm-100mm. It is very important that the prime window is as draught-proof as possible or the effectiveness of having secondary glazing will be reduced.

To further cut down noise, you can fit acoustic tiles around the perimeter of the reveal, that is, around the top, bottom and sides between the prime and secondary. These are easily and cheaply obtained from suspended-ceiling firms, and if you are lucky you may be able to pick up some damaged tiles cheap that you can cut to size. Leave a small gap, say 5mm, between the tiles and the window frames.

Good-quality secondary glazing does not come cheap, after all, it is almost like having a new window. I prefer aluminium secondary frames because for really effective noise reduction it is desirable to have as much rigidity in the frame as possible. Aluminium frames are available in silver, dark brown and white and, as far as I am aware, in several other colours.

More on noise reduction
If you are not interested in fitting secondary glazing but want to reduce noise more than the average double-glazing window will, the best way is to have the double-glazed sealed unit make-up changed. Instead of: 4mm - air gap - 4mm, have: 4mm - air gap - 6mm. Notice I do not mention the air gap thickness, which is of little importance when it comes to noise reduction as the small differences in available gaps in double-glazed sealed units are almost insignificant.

If you have old-single glazed windows and wonder how well normal new sealedunit double-glazed windows will work, then you are probably in for quite a surprise. If you have only ever had single glazing and can't understand what all the fuss is about with 'double glazing', I can tell you now that the likelihood is that the noise and heat reduction you will gain will probably far exceed any modest expectations and preconceived ideas you may have.

A lot of secondary glazing is fitted when properties are suffering excessive noise pollution from proximity to airports or to a new road-building scheme.

Typically there are two ways to install the secondary frame, either fixing to the existing framework (face fix), and remember to leave sufficient gap for the handles, or reveal fixing, where the fixings will go into the wall. The latter method will more likely provide for the wider gaps.

The nuisance with secondary is that because the air space is not hermetically sealed the panes need to be removed periodically for cleaning. Also, of course there is ventilation to consider. Secondary glazing is no good when you have it slid open and your main window is also open for some air.