Double Glazing or not?

[spanner48]

One solution to your problem may be a new technique: VACUUM INSULATED GLAZING, or VIG. It's two sheets of - typically 4mm - glass, with a 0.3mm gap between them, pumped out to a vacuum. The two panes are kept apart by tiny 'pills' of transparent glass frit placed every inch, in a square pattern. You get an 8.3mm pane that is as thermally effective as wide double - or even triple - glazing. And it is also as effective a sound barrier as triple.

ADVANTAGES

• It fits almost everywhere in place of standard - typically 6mm - glass. No need to modify casements; just reduce the putty by 2mm

• It is no heavier than standard 8mm single pane

• Except under the minutest inspection, it is indistinguishable from single glazing

• Installation is easier. The edges are sealed with fused glass frit, so no need to worry about ventilation and drainage around the panel - as with conventional DGUs

• Durability is better than - particularly - narrow-gap DGUs. These have gained an evil reputation for failing after only a few years, due to the uneven heating and cooling of the outer and inner panes shearing the perimeter bond. By contrast, VIG units are routinely guaranteed for 20, 25 or 40 years. Experience so far is that failures are rare.

DISADVANTAGES

• It's not cheap. Typically at least 50% more than conventional DGUs, on an area basis

• Minimum panel size for pricing is 0.7 m^2. So redoing mock-Georgian sashes is either very expensive, or involves milling the muntins' fronts back, putting a single pane over all, and adding astragals

• They have to be ordered, individually, from the Far East [Korea, Japan, Taiwan, China]. So delivery is slow

• The UK glazing trade hasn't heard of it, and is reluctant to work with VIG. I know of only ONE experienced installer south of Coventry . . . .

For brands, see Pilkington 'Spacia'; Landglass 'LandVac'; 'Guardian'; Asahi 'Fineo' etc.

I've used it, once. The results - so far - have been good.

 

[Doug71]

Does the Spacia glass still have the little cover cap on it? I have customers moan about the stamp to show that glass is toughened so don't know what they would think to the little cap on each pane.

 

[KieranJW]

My opinion on that system is that it’s far more complex than is needed. If you research the design requirements for good non sealed units you have almost the complete benefits of IGUs while using 2 panes and can easily use different thicknesses to help with sound control and you only need a single casement. If you want to add on shutters you can sill do that.

Thanks that is something I originally muted but then I was persuaded out of it by fellow tradesmen! My reasoning was that you needed a good hermetic seal and possibly dessicant other than that it was just my own thoughts really.
Where should I be looking for this information? Have you a source?

 

[KieranJW]

I renovated some vertical sliding shutters some years ago. They didn't know they were there at first and were puzzled by the unused sash pulleys. The shutters dropped into a pocket behind the panelling and the lid closed looked like a normal window cill. They were quite big and dropped below floor level in their boxes.
Re condensation - there's a good argument for saying that it's better to have it on your sash windows rather than on the walls. It drains off and drips away through meeting rail gap and at the bottom sash. You can sometimes see icicles forming outside where it drips. So the single glazed window acts as a de-humidifier.
Also brilliant for draught control and I think Florence Nightingale noted these features and highly recommended them for health reasons

Thanks I've seen shutters like that before.

 

[KieranJW]

One solution to your problem may be a new technique: VACUUM INSULATED GLAZING, or VIG. It's two sheets of - typically 4mm - glass, with a 0.3mm gap between them, pumped out to a vacuum. The two panes are kept apart by tiny 'pills' of transparent glass frit placed every inch, in a square pattern. You get an 8.3mm pane that is as thermally effective as wide double - or even triple - glazing. And it is also as effective a sound barrier as triple.

ADVANTAGES

• It fits almost everywhere in place of standard - typically 6mm - glass. No need to modify casements; just reduce the putty by 2mm

• It is no heavier than standard 8mm single pane

• Except under the minutest inspection, it is indistinguishable from single glazing

• Installation is easier. The edges are sealed with fused glass frit, so no need to worry about ventilation and drainage around the panel - as with conventional DGUs

• Durability is better than - particularly - narrow-gap DGUs. These have gained an evil reputation for failing after only a few years, due to the uneven heating and cooling of the outer and inner panes shearing the perimeter bond. By contrast, VIG units are routinely guaranteed for 20, 25 or 40 years. Experience so far is that failures are rare.

DISADVANTAGES

• It's not cheap. Typically at least 50% more than conventional DGUs, on an area basis

• Minimum panel size for pricing is 0.7 m^2. So redoing mock-Georgian sashes is either very expensive, or involves milling the muntins' fronts back, putting a single pane over all, and adding astragals

• They have to be ordered, individually, from the Far East [Korea, Japan, Taiwan, China]. So delivery is slow

• The UK glazing trade hasn't heard of it, and is reluctant to work with VIG. I know of only ONE experienced installer south of Coventry . . . .

For brands, see Pilkington 'Spacia'; Landglass 'LandVac'; 'Guardian'; Asahi 'Fineo' etc.

I've used it, once. The results - so far - have been good.

Wow sounds really good. I will look into it. I have used histoglass a couple of times in the past when fitting with a colleague. I personally havent had a comeback yet but he had two enormous projects where a majority of the units failed. He followed all the guidance from the supplier and is extremely good at what he does so this has put me.off using them at all.

 

[ian33a]

I think your figures may be out of date - my new windows have argon filled 4mm - 20mm - 4mm panels, which I was told is the optimum gap.

Not sure about that Phil - there are plenty of papers on the internet stating that 12mm is optimal for argon. At one time, and I'm not saying that you were seduced by the salesman, the "bigger is better" approach was sold. I stand by 12mm as the optimal gap. Not that I'm suggesting you need to order a thermal vest and mittens for the coming winter as the difference wont be that noticeable.

Up to a point you can have a bigger spacing but you quickly reach a point where convection of air/argon/whatever becomes a problem. The tumbling of the content between the panes causes a cold outer surface (1/2) to migrate through to the inner surfaces (3/4) by way of convection and causes condensation and/or cooling in the room. A low E coating on surface 3, to some degree, mitigates the temperature drop and keeps surface 4 warmer and this, in turn, reduces internal condensation.

You will be fine with a 20mm gap, but 12mm is generally considered optimal.

 

[sometimewoodworker]

Re condensation - there's a good argument for saying that it's better to have it on your sash windows rather than on the walls.

condensation is not inevitable. If your walls don’t get cold enough you will not have condensation on windows or walls. That rather kills that argument, doesn’t it?

 

[ian33a]

condensation is not inevitable. If your walls don’t get cold enough you will not have condensation on windows or walls. That rather kills that argument, doesn’t it?

Agreed. Equally, if you properly ventilate a room, you wont get condensation either

 

[sometimewoodworker]

Thanks that is something I originally muted but then I was persuaded out of it by fellow tradesmen! My reasoning was that you needed a good hermetic seal and possibly dessicant other than that it was just my own thoughts really.
Where should I be looking for this information? Have you a source?

Sorry no, but if you research places like the Nordic countries. Also the information I recall did not have hermetic seals or desiccant. It relied on the correct design of ventilation between the glass and allowed moisture to escape.

nowadays the technology may have disappeared due to the ease and ubiquitous availability of IGUs so you may need to do historical research.

I am sure that the systems existed, maybe still do. However the information I read was years ago and I have no idea were I read it, possibly in one of the woodworking magazines.

 

[sometimewoodworker]

Agreed. Equally, if you properly ventilate a room, you wont get condensation either

It’s actually reasonably easy to know how to avoid condensation.

Keep all surfaces above the dew point of the air in a room.

Now the ways to do that are many and various but the principle is science (physics) 101

 

[ian33a]

It’s actually reasonably easy to know how to avoid condensation.

Keep all surfaces above the dew point of the air in a room.

Now the ways to do that are many and various but the principle is science (physics) 101

Totally agree, I have lost count of the number of times I have explained dew point and condensation to customers who seem to think that hermetically sealing their properties is the way to go. I even prepared a PowerPoint slide to try to explain it to them. Sadly, too many of them had a closed mind set.

 

[Phil Pascoe]

You will be fine with a 20mm gap, but 12mm is generally considered optimal.

Interesting.
The 28mm double glazed window is currently marketed as the best option around. That is a combination of a 20mm air gap plus the glazing (2x4mm) .................... a quote from a random site, although another states that 12mm is the optimum.
The (quite large) firm I bought from has all their panels made with 20mm gaps unless otherwise specified - I can't imagine they would do it without reason as for one it would make the frame sections heavier and therefore more expensive.

 

[Phil Pascoe]

Totally agree, I have lost count of the number of times I have explained dew point and condensation to customers who seem to think that hermetically sealing their properties is the way to go. I even prepared a PowerPoint slide to try to explain it to them. Sadly, too many of them had a closed mind set.

We used to drive past an estate agent's window with a sign saying "We can cure your condensation problems for just £499" I used to say to my wife if they bought me a couple of pints I'd tell them how - open their ****ing windows.

 

[ian33a]

Interesting.
The 28mm double glazed window is currently marketed as the best option around. That is a combination of a 20mm air gap plus the glazing (2x4mm) .................... a quote from a random site, although another states that 12mm is the optimum.
The (quite large) firm I bought from has all their panels made with 20mm gaps unless otherwise specified - I can't imagine they would do it without reason as for one it would make the frame sections heavier and therefore more expensive.

It was along the lines of what I thought Phil TBH. So many companies have massive manufacturing runs done in the same way that they have always done it. The economies of scale give them a better price point and then its a marketing exercise to sell a suitable benefit to customers. Standardising on certain sizes and styles makes sundries such as packers, window furniture and seals inventories smaller (and thus running costs cheaper) and fitters don't end up making as many mistakes.

When we had our windows changed 10 years ago we were sold a whole host of stuff based upon what the salesman (company owner) told us. At the time it all made sense. A couple of years later and we started a glazing repair company and my engineering background caused me to research very heavily (that, and the need to pay the mortgage!). I discovered that so much of what I was told was misinformation or semi rot. I don't blame the salesman, I think he did what he thought was right. Trouble is, the industry is riddled with myth and bad practise.

 

[Jacob]

condensation is not inevitable.

In certain conditions it is highly probable

If your walls don’t get cold enough you will not have condensation on windows or walls. That rather kills that argument, doesn’t it?

Er..no?
If your walls aren't as cold as your windows you will get condensation on the windows, if conditions are right for condensation.

 

[Jacob]

It’s actually reasonably easy to know how to avoid condensation.

Keep all surfaces above the dew point of the air in a room.

Now the ways to do that are many and various but the principle is science (physics) 101

Not even science is just logic. Keep all surfaces above dew point i.e. the temperature at which condensation will form. But not actually any help.
Frinstance if you boil a kettle the dew point temperature falls even as the temperature in the room rises.

Dessicants in DG unit are pointless - if the thing leaks it will slightly delay the point where you get condensation within, but won't stop it.

 

[RobinBHM]

The 28mm double glazed window is currently marketed as the best option around. That is a combination of a 20mm air gap plus the glazing (2x4mm) .................... a quote from a random site, although another states that 12mm is the optimum

above a 16mm air gap, the air inside starts to circulate by convection so 20mm and over doesnt improve u values -although I think argon with a 20mm air gap is about the sweet spot -pretty much all Upvc is 20mm air gap these days, most timber is 24mm.

 

[RobinBHM]

Dessicants in DG unit are pointless - if the thing leaks it will slightly delay the point where you get condensation within, but won't stop it

its purpose is to remove residual moisture trapped into the unit during manufacture.

 

[RobinBHM]

Keep all surfaces above dew point i.e. the temperature at which condensation will form

pretty difficult with just 4mm glass between the outside world and the inside

glass is only about 5x less conductive than steel

 

[Jacob]

pretty difficult with just 4mm glass between the outside world and the inside

glass is only about 5x less conductive than steel

Well it's a mystery to me that we don't have a condensation problem here, single glazed throughout some of it down to 3mm!
Sometimes see the odd patch on a cold morning but it's gone by the time I've made a cup of tea.
I did design in a drainage system with a drip catch runnel draining to the outside but it doesn't seem necessary - except for the odd very cold morning when it gets a little puddle briefly.