Is double glazing worth having?  Won’t it be cheaper to have single glazing?

These are two questions that I am asked quite frequently. The answer to both is yes.

Although both answers are ‘yes,’ the first question is the important one, so let’s deal with that one first.

Is double glazing worth having?

Double glazing works by trapping air between two panes of glass. This trapped air creates an insulating barrier which serves three functions:

  1. First of all it prevents heat loss or gain through the window because the barrier insulates the room from differing air temperatures at either side of the glazing unit.
  2. Secondly, double glazing helps keep noise pollution down.
  3. The third benefit of double glazing is that it helps reduce condensation. Condensation commonly occurs on the inside of single glazed windows due to the warm air inside the house being cooled by the cold outside air. With a double glazed window the insulating barrier prevents the transmission of air temperature and therefore helps prevent condensation occurring.

Although double glazing insulates against differing air temperatures, it does not insulate against radiant heat. This makes a double glazed unit a good choice for permitting winter sun to warm the inside of the house whilst at the same time insulating from the cold outside temperature.

So, back to the second question.

Won’t it be cheaper to have single glazing?

Of course it will be cheaper but it will also have a poor thermal performance and you will end up endlessly wiping condensation off the inside face of the window during the winter months. Also, just remember, if you’re not motivated to wipe the condensation away you will end up with mould growth which in turn will cause health problems for your house and its occupants.

This may seem like a pretty strong point of view on glazing but just consider the following points:

  1. Current thermal requirements for external walls states a minimum insulation value of R2.8. We achieve this with wall insulation. A typical aluminium framed, single glazed window has an R-value of R0.15. That’s over 18 times less than the wall next to it. So, if you’re going to insulate your walls, it makes sense to insulate your windows with double glazing.
  2. A consequence of highly insulating and draft sealing our homes is the increased risk of condensation. condensation will occur on the thermally inefficient windows. Double glazing goes a long way towards mitigating this risk.

If you are trying to cut costs on your building project, be careful when choosing your windows. A budget based decision might be good in the short term but you will certainly pay in the long run.