Condensation behind new secondary glazing

[BlogOnTheTyne]

My builders promised me that this wouldn't happen and even now are saying that the new secondary glazing is fine and that condensation build up behind the panes is because the room has recently been plastered/painted etc.

The glazing panes have been put up over old glass, decorative and unopening windows. From the start, I was worried that there'd be a build up of moisture between the panes as this happens in older parts of the property where there is secondary glazing. It's an uphill struggle stopping the mould and rot.

My builders say that they were told by the window company that the close fit of the secondary glazing will prevent this happening in the new build. However, there's a noticeable gap between the 2 panes and the condensation build up is already leading to pooling and run off and wetting the new paint around the windows. I predict that by the end of the winter, I'll have mould and rot. There's also a bit of a draught too around the secondary glazing.

Builders insist that this is only a temporary issue and will resolve once the new build has 'dried out'.

Do I pay them (they're just at the end of a big project here) or retain some money until we can prove that the condensation issue isn't a problem?

I don't want to be forever removing the secondary glazing and drying behind it, as the little plastic 'hooks' that attach it look v flimsy and in older parts of the house, I find that if you keep moving the glazing, they break off.

Any advice please?

Hmmm. I have secondary double glazing and I would be terribly unhappy if I were getting pools of water behind it.

Our windows are quite large (about 3m across) and have a series of sliding panels which can be removed but there are definitely no gaps. I mean what would be the point of that ?

I like to open my windows in the summer and warmer days to air the room and the bedroom / shower room often results in condensation forming in the void which has to be wiped. But its never enough to be pooling.

Can you get some advice from window company first ? I wouldn't be convinced that the builders are being entirely honest with you.

The draughtproofing needs to be changed. The cavity between the panes needs to be sealed as effectively as possible from the room, but allowed to ventilate to the outside air. If your old windows were non-opening (how did you ventilate the room?) they may need trickle vents or small holes drilled through the frame.

Plaster, mortar and emulsion paint are all made of water plus other ingredients which needs to be ventilated away while it dries.

Thanks. I don't even know who the window company are but will ask my builders for their details.

Re. trickle vents, I asked the builders about those as they've got one in a new skylight and have opened another skylight a fraction, permanently (an older one without trickle vents) and said that this will allow ventilation.

The newly secondary glazed old windows weren't and aren't the only windows so didn't need to be opened before. However, this was a garage/den that has now been properly converted and now is properly heated and will be used fully.

If small holes were drilled in the frames of the unopening windows, won't that allow cold draughts of air in and a loss of heat? If trickle vents were put in, what would they need to do to achieve this (window is a circular shape) and would they protest at having to revamp the frames again?

the amount of air that passes through a drilled hole is quite small. It will not be enough to make your room cold. There will still be a space of still air between the inside and the outside panes which will cut heat loss.

The "inside" pane has to be sealed better that the "outside" pane so that the space is filled with "outdoors" air which, being colder, holds less moisture.

allowing warm, moist, "indoors" air into the space will cause condensation.

when drilling a hole in a wooden window frame, it has to be angled downwards to prevent water running in, and preferably in a spot where rain does not beat against it. You can poke a scrap of mineral wool in the hole to keep out dust and insects if you want. If you still get condensation (depends on airflow direction) a hole top and bottom will help.

Thanks v much. V helpful as usual. Now I've just got to persuade the builders to recognise the problem rather than playing it down and saying it'll clear once the room has dried out.

As a grade 2 house My single glassed leaded windows had to be replaced exactly the same as the old ones. We did this and had secondary glazing added. This means there is an air gap between the outside and the inside which has usually been fine. This year, however even though nothing has changed regarding heating, occupants of bedrooms etc., the inside of the windows have significant condescension on them every morning. Moisture in the outside air seems to be very high at the moment. The question ‘is this due to climate change’ or a breakdown in the leads on the outside of the windows meaning more cold, moist air is hitting the warmer air in the gap before the secondary glazing. Anyone had the same situation or any hints or helpful suggestions/information would be appreciated.

it needs ventilation to the outside like I said.

Other factors can be deterioration of the window set allowing rain penetration; or an occupant throwing buckets of water at the walls, or draping wet washing on radiators, which amounts to the same thing.

How is the room ventilated?