Condensation inside secondary glazing.

[88v8]

Our windows are all single glazed, lead lights.
Each is different, so I'm having to devise different solutions in making secondary glazing to stop the condensation with which we're plagued. Even now, with the rh around 45% - low, for our cottage - some of the windows are running with water in the mornings. Earlier in the winter, before the woodburners had dried the house, the rh was >60% and the windows were like little Niagras.

I finished my first window last week, a fixed casement in the dressing room, using a secondary woodframed panel glazed with glass and sealed against the frame with expanding foam tape.
Before fitting, I dried with paper tissues and a hair dryer.
However, from the first day, there was slight condensation in there, and as I write all the windows in the house are clear... except the one with secondary glazing :shock: which has condensation in it. Enough that it's beginning to run down the glass, which is exactly what I was trying to prevent. It seems that water vapour is getting in, but can't get out.

Here
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4958
it's suggested that the original window needs to be vented to the outside. If it's not an opener - it's not - this would necessitate drilling holes.
However, the participants in that discussion can't agree amongst themselves.

Years ago, I fitted some secondary glazing in our previous house, it was not particularly well sealed but never had this problem. However, that was a relatively modern house, centrally heated and not damp.
Has anyone here any experience of this problem, and any solutions?

Ivor

 

[Lime]

Nearly all double glazing and secondary glazing requires some sort of drying agent ( desiccant) within the sealed cavity.
Silica gel and calcium chloride are the most common ones but there are others.

As you say, the water vapour gets into the secondary glazing cavity but cannot get out.
Making holes in the window so that the water can escape will defeat the purpose of the additional glazing to a very large extent.
Most double glazing has some sort of provision for holding desiccants in a perforated bar/separator between the glass panes.
DIY secondary glazing sometimes has simple holes in the frame filled with desiccant.
However if water vapour is getting into the cavity in large amounts the desiccant will need to be rejuvenated/regenerated regularly.

 

[MatthewC]

Even now, with the rh around 45% - low, for our cottage - some of the windows are running with water in the mornings. Earlier in the winter, before the woodburners had dried the house, the rh was >60% and the windows were like little Niagras.

Even 45% RH sounds high to me. I have no idea of what it is in my house, but I do know that it did take more than a year to dry out. Is your house still damp for any reason or do you consider it dry?

Anyone else have any idea of what their house's RH is?

 

[88v8]

Even 45% RH sounds high to me. I have no idea of what it is in my house, but I do know that it did take more than a year to dry out. Is your house still damp for any reason or do you consider it dry?

Anyone else have any idea of what their house's RH is?

Cheap enough to find out. And worth finding out, as anything below 30% is bad for antique furniture, panelling, etc.
http://www.amazon.co.uk/LCD-Digital-Temperature-Humidity-Thermometer/dp/B004GN9EH2/ref=sr_1_2?ie=UTF8&qid=1364895199&sr=8-2
and anything above 60% will lead to mould etc.

Yes, I'd say it's damp. The rh in the cellar is over 60%, nothing to be done about that, and that's directly below the kitchen - no door - and high ground level at the back of the house so the back wall is damp, the walls are stone with no dpc, the floors are solid with no dpm, oh, and theres no extractor fan yet in the kitchen and there is and will be no kitchen door.
So, I think 'damp' would pretty much sum it up

But I did assume I could at least stop the condensation

Lime, thanks for the tip about silica gel. As you say, it would have to be dried out regularly, and the moisture would then go, errm, back into the air inside the cottage... hmmmm...

Ivor

 

[Greg.Hobson]

Regarding RH.

My Weather Station is cheap and cheerful and is beginning to give erratic readings - which are very easy to spot! - but is fun to have around. My internal RH as I type is 50% on the dot.

Other data is at http://www.Greg-Hobson.co.uk/Weather for those interested.

Greg Hobson

 

[Penners]

I agree with everything that Lime says above. You can never achieve a stable low humidity between primary and secondary glazing. There will always be air leaks through the primary window (which presumably has opening sashes) that bring water vapour in with them.

As well as sealing the secondary window in place, try to draught-proof the primary window as effectively as you possibly can. As Lime says, you should also have some strips or trays of dessicant (eg: silica gel) between the two windows. But, even though you should find that this will substantially ameliorate the condensation problem, there's no way of guaranteeing its complete absence.

 

[MdB]

There will always be air leaks through the primary window (which presumably has opening sashes) that bring water vapour in with them.

Condensation is more likely from house air moving into the gap via the secondary glazing as it will cool when it gets there. Outside air is more likely to warm up so won't condensate. At least, that is the theory.

There is more moisture in 20°C 50% humidity house air than there is in 0°C 100% humidity outside air (by a factor of 2!)

 

[worms]

I once worked in an office with 1950s wooden double-glazed windows. Small individual panes, each puttied in place. The amazing thing was that some of the panels were almost completely full of water. I would have expected that they would reach an equilibrium where the condensation on the outer pane came only from the humidity between the panes, but clearly this was not the case, or not reached until the gap was almost completely full of water.

I spent a lot of time staring out these windows trying to figure it out!

 

[Penners]

Presumably if the "sealed" unit DG panels were completely full of water, they were optically correct! I wonder what their U-value was.

 

[worms]

Presumably if the "sealed" unit DG panels were completely full of water, they were optically correct! I wonder what their U-value was.

Actually, yes! You could see better out the water-filled ones than the dry ones. I guess it was testament to the build quality that the wood had held and was capable of holding the water, but they were not sealed units - the glazing bars had a rebate to both sides and were glazed from outside and inside, with identical sized pieces of glass.

 

[88v8]

There will always be air leaks through the primary window (which presumably has opening sashes) that bring water vapour in with them.

Condensation is more likely from house air moving into the gap via the secondary glazing as it will cool when it gets there. Outside air is more likely to warm up so won't condensate. At least, that is the theory.

If I put a small pump in between, drawing air from outside, that could create a slight positive pressure between inner & outer panes, so no water vapour getting in. Or better, the pump could sit in the room, with a suction pipe to the outside, and a pressure pipe into the glazing. Would only need to be quarter inch, and run intermittently. Hmmm.
How about an aquarium pump? They're pretty quiet.

Where can I get an intermittent timer? I remember having trouble finding one before... not that I can recall why I wanted it...

Ivor

 

[Penners]

88v8 - I have a small concern that we may getting into the territory of over-engineering, here!

 

[agbagb]

A small hole or holes to the outside is the way to go. (pluged with loose bit of rockwool to stop the creepy crawlies)

The problem you will solve is a pumping action that feeds moist air in. The Air between the glazing expands and contracts with every temperature change, including clouds shadowing the sun. As the air contracts it draws in air from the most easy route which is likely to be your secondry glazing seal. The moisture condenses and dry air gets pumped out when the sun comes back out and the cycle starts again.

Venting to the outside, and a good seal to the inside solves the problem.

(worrms, its why those windows filled up and why modern double glazing can mist or fill up from the tinyest breach of the seal)

 

[88v8]

A small hole or holes to the outside is the way to go. (plugged with loose bit of rockwool to stop the creepy crawlies)

Sounds logical.
Drilled a quarter inch hole through the frame, slight downslope. This morning, steamed again. Perhaps less rockwool, or none as a trial.
Onwards....

Ivor

 

[agbagb]

It's likely that the timber will take some time to dry, so that could cloud the results for while. A desicant should help in the short term.

 

[88v8]

Just to update....
As far as I can see, and it will need next winter to confirm or otherwise, the drilling did the trick. The window steamed a little in the corner diagonally opposite to the hole, otherwise not.
Pressing on, slowly, with other windows. As no two are alike, each needs a variation on the theme.

The rear window in the bedroom had rot along the elm sill going down a good inch right below the glass, the result no doubt of condensation over the last 100+ years. Had been filled with putty, and what looks like Woodflex, a favourite of PO.
Now resin & two-part filler.
Onwards....

Ivor

 

[CliffordPope]

I agree about small holes to the outside being the best solution.

But i do have the suspicion that if you stop the condensation on the windows, by DG them, it will simply go somewhere else less visible but more damaging, ie the walls.

After years of experimenting I have reached two conclusions:

1) DG should be seen as a weapon against heat loss and noise, not condensation
2) The only real cure for condensation is a dehumidifier

Obvious that's after dealing with direct sources of damp, like soil build-up, leaking pipes, underground streams, etc.

 

[88v8]

I agree about small holes to the outside being the best solution.
But i do have the suspicion that if you stop the condensation on the windows, by DG them, it will simply go somewhere else less visible but more damaging, ie the walls.
After years of experimenting I have reached two conclusions:
1) DG should be seen as a weapon against heat loss and noise, not condensation
2) The only real cure for condensation is a dehumidifier.
Obviously that's after dealing with direct sources of damp, like soil build-up, leaking pipes, underground streams, etc.

Mmmm, you may be right. High soil level, check. Underground streams, check.

In the process of rectifying the former - LBC application in hand as part of a building campaign - we may find that the latter is land drains rather than streamlets, or could be both. We live on the side of a steep hill, already had to put a land drain & sump pump under the stone stairs in the cellar, and there is another ingress into the opposite corner of the cellar. In winter, the lane from the hilltop constantly runs with water, even a week after the last rain.

If water condenses elsewhere, we will get more mould. Surprisingly little, at present. We shall see, or not as one always hopes.

The other danger with DG is the temptation to stop what may be wrongly referred to as 'draughts', but are in fact essential ventilation.

Ivor

 

[DJH]

Here's a tip from the 1950's to stop draughts in sash windows. Maybe a dessicant could be substituted for sand in the bags??





Doug

 

[Penners]

I'm deeply shocked to see that the gentleman carrying out DIY in the upper picture has removed his jacket! :shock:

Whatever happened to standards?