Reply To: Condensation on room facing side of secondary glazing film

[Ian McChesney]

Hi Jo
I’ve had plastic film secondary ‘glazing’ in my house in Christchurch for quite a few years and experience the same thing occasionally. The condensation is always at the bottom of the glazing, which is the coldest part of the window – is that your experience?

I’ve put it down to this:
– sharp drops in outside temperature following warmish, humid weather where the house may have been quite warm and the air in the house may be carrying a lot of moisture (the warmer the air the more moisture it is capable of holding – remember RH readings only tell you the amount of moisture in the air relative to the maximum amount it can hold at that temperature). In these conditions condensation on windows may occur at high indoor temperatures than you might normally experience.
– your v good curtaining will be exacerbating the likelihood of condensation. They do a great job of keeping the room heat away from the window (which is their purpose), but the down side is that the window surfaces (including the secondary glazing layer) can get colder because they don’t have exposure to the warmer air in the bedroom, and hence be more prone to some condensation, sometimes
– note also the bedroom will have extra moisture load during the night because of sleeping bodies.

So, what you describe is similar to my own experience. I just put it down to these circumstances that will occasionally cause some condensation, and continue to have confidence in the product(s). I continue to use secondary glazing and recommend it. I presume the secondary glazing in other parts of the house is still performing OK?

If the problem persists, say on one window more than another, or if the fogging between the glazing becomes more consistent, it could mean the secondary glazing airtightness is compromised and needs attention.

Whether there are other moisture issues in your house exacerbating the problem? Difficult to tell at this stage, but if there were I would think there would be other signs of dampness in the house e.g. mould in wardrobes etc.

Hope this helps

all the best
Ian

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