Would double glazing tackle a damp problem around my windows?

I have an old house with bay windows and single glass panes and have a problem with dampness. It is really confined to the area under and above the bay windows. I have considered dry-lining, but feel I would lose some of the characteristics of the rooms such as skirting boards, covering etc. My query is: if, instead of insulation, I changed the windows to double or triple glazing, would this solve the problem? I want to make the decision before another damp winter comes.

The first question to consider is whether the problem is related to dampness, ie water penetration, or due to condensation. By dampness, this normally means either water penetration from the exterior through the bay structure or from within due to, say, a plumbing leak. As regards the exterior, water could be coming in through the roof to the bay window, or through the walls either due to defective external finishes or by rising dampness. Alternatively, water penetration could be due to poor seals at the window frame/wall junctions.

Whilst replacing a window would most likely involve an improved seal at a window frame/wall junction, it would not actually have any material effect on other causes of water penetration and you will need to ensure that there are no active sources either from the exterior or from within.

Condensation, on the other hand, is caused by the “environmental conditions” created within the property and, whilst there are a number of contributory factors, poor insulation standards such as that provided by single-glazed windows would clearly give rise to high levels of condensation, which could well be contributing significantly to the dampness here.

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In such cases, replacing the windows with double or triple glaze would clearly alleviate or at least significantly reduce the problem. The only caveat is that with older properties, there is very unlikely to be any insulation within the wall and thus there will be a risk of some cold bridging in the walls which can give rise to some condensation/mould growth.

It is, however, our considered view that when refurbishing properties, this is not an exact science, and a holistic view should be taken in order to get the best compromise solution. It is necessary to weigh up the pros and cons of completely eliminating a potential cold bridge, and the aesthetics/characteristics of the room.

In this respect, if you were to dry-line or insulate the bay window then you will lose the original timber panelling / moulding. At this stage, we do believe that replacing the windows in isolation will significantly reduce the problem to the point where an acceptable solution can be reached without having to lose the original ornate feature/characteristics of the room.

If, in the unlikely event that you still experience some dampness or mould growth, a later decision can always be taken regarding the need for incorporating any dry-lining systems within the bay window area.

Val O’Brien is a chartered building surveyor and member of the Society of Chartered Surveyors Ireland, scsi.ie