Listed Building - Secondary Glazing, Condensation/Misted Up Inside

if the glass does not press tightly against the glazing bars, you might try drilling through the central bar.

If it does, you could groove the bar just enough to permit air to pass.

There are defogging systems used in the US where they drill the outer pane with a diamond bit, and insert insect-proof breathable plugs. This seems to be done on DG shop windows, where a new unit would be particularly expensive.

Breathing to the outside is key. Expansion and contraction as the air in the cavity warms and cools is all it needs. I have done a few. I still have one that I did over 20 years ago and it does not mist. I have not opened it since the day I did it.
 
Diamond Drill method

You don't need to go to such trouble. You just need a breathing hole.

Replacement sealed units are not as expensive as you might think, which might be why the idea hasn't taken off over here.
 
Thanks JohnD - very helpful. Will see what I can do with the drilling. Thanks so much for your help (and very interesting!)
 
JohnD said:
Diamond Drill method

You don't need to go to such trouble. You just need a breathing hole.

Replacement sealed units are not as expensive as you might think, which might be why the idea hasn't taken off over here.
Click to expand...

The reason it hasn't taken off is because its a con. Yes its a cheap fix for misted up units but its no longer a sealed unit so you loose most of the thermal benefits.
There are lots of arguments about it all over the internet (mainly started by the creators) but the experts have concluded its pointless. There used to be a great web site that went into all the technical details of both this and the super slim double glazed units but it seems to be gone now.

Oh and that video wont play in the UK for some reason.
 
Gazman16 said:
you loose most of the thermal benefits.
Click to expand...

No you don't

The air inside is almost stationary (it is too narrow for convection circulation) so it is just a pocket of still, insulating air.

Secondary glazing is also unsealed.

The first time I added an extra pane to a wooden window was in a bathroom. As well as cutting heat loss, I was amazed that the window stopped running with condensation, and just got a little light misting on the room side when running a bath. It is much easier to DIY on a non-opening window, at trivial cost, but interest in these techniques has dropped since the commercialisation of DG by the big installers.

The incremental benefits of hi-tech glass and gas-filling don't make such a big difference as the first extra sheet of glass and pocket of air.
 
I agree with Gazman , the drilling method is pointless... the correct method was always to drill a hole top and bottom , so that a gas/fluid could be injected to remove the moisture and coat the glass to stop it building up again. If the air is stationary you will not be removing the water vapour, it needs an airflow to move, hence the properties of the hermitically sealed unit would be pointless, plus how do you stop the small glass fragments falling into the unit ? Modern day units are made with soft coat low e... If you have ever seen that in a single glazed form after a few days of being exposed to the envirionment then you would certainly not recommend this ' hole fix' as the softcoat would eventually look awful.
How are you getting around Toughened glass, you can't drill holes in that.......
And its amazing how , when i looked into this idea for our company years ago , the company we would have been for couldn't answer the questions about the lack of thermal properties once the holes were drilled.
Another point to make is , if your ' sealed unit ' has already started to show signs of the glass going white , then this drilling method is NEVER going to solve it

A Good secondary glazing is sealed using the brushes on the system ( but the original windows may not be sealed so well .........) , but is also ' generally ' opened regularly to access the original windows, so the extra water vapour is allowed to escape......
 
However this thread is about secondary glazing, not sealed units.

A tiny breathing hole from the cavity to the outside enables natural expansion and contraction to ventilate it and prevent misting. It's easy because you can drill through the frame not the glass. The window does not need to be opened for water to escape.
 
Just to give everyone an update, I found a solution. As the glazing tightly covered the glass pane, there wasn't anywhere easy to drill a hole through without risking cracking the glass. However, I managed to drill a hole at an angle. So with the window open, I drilled a hole at 90 degrees through the side of the window casement into the window cavity. Now, naturally, with the window closed, this doesn't leave a lot of ventilation as the hole will be blocked. However, I placed a very narrow (2mm) plastic tube through the hole, and to the outside (just glueing it to the casement so it stays in place).

After adding it to both panes, the misting lifted in a couple of days, and it hasn't come back in over 2 weeks.

Might come in useful if anyone has the same problem.
 
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