Double glazing in a front door

[dexter]

Can anyone advise me on the minimum thickness a double glazed unit has to be to go into an exterior front door? All the research I`ve done today tends to suggest that it`s 24mm (16mm gap and 2x4mm panes). The door I`m making will be 45mm thick, it`s going into an existing frame in a glazed porch so no possibility/budget to replace the whole porch. If it is 24mm for the unit its going to be a bit tight to bed the glass to the rebate and fit a very thin glazing bead.
Thanks in anticipation.

Dex

 

[Dibs-h]

24mm - I wouldn't have thought so. It depends on whether the door is for you or someone else. If you, you can get ones with a 6mm spacer instead of a 16mm one.

For someone else - can't say TBH.

HIH

Dibs

 

[AndyT]

I rather think the answer depends on the building regs and who is interpreting them. Also, you can generally replace like with like. So if you had an existing door, with an old d/g unit of say 4+10+4, you would be allowed to replace it with an equivalent, even if that spec would not strictly be allowed for a new build. Of course your glazier can't see the door, and will just make up what you ask for.

But this is only from my limited experience and I'm not an expert on building regs, and don't have to complete forms to show what I have done.

 

[RogerS]

Sounds like a repair to me and so not covered by Building Regs. Depends how low you want to go in terms of u-value. If your research was only suggesting air-filled and normal glass then you'd get the same or better u-value if you went with something like k-glass and argon. Don't forget if it goes all the way to the floor then it needs to be toughened.

 

[dexter]

The problem is that the door is`nt for me. It`s for an old mate who`s on a very very tight budget after being made redundant.

Dex

 

[clewlowm]

Sounds like a repair to me and so not covered by Building Regs. Depends how low you want to go in terms of u-value. If your research was only suggesting air-filled and normal glass then you'd get the same or better u-value if you went with something like k-glass and argon. Don't forget if it goes all the way to the floor then it needs to be toughened.

should be toughened anyway. door or side light. also the op would be better off using 4/6/4. super spacer. with a low iron glass and argon filled. cost is circa £80 per square metre.

http://www.warmedgeunits.com/safety.html

 

[RogerS]

Sounds like a repair to me and so not covered by Building Regs. Depends how low you want to go in terms of u-value. If your research was only suggesting air-filled and normal glass then you'd get the same or better u-value if you went with something like k-glass and argon. Don't forget if it goes all the way to the floor then it needs to be toughened.

should be toughened anyway. door or side light.

depends on whereabouts in the door it is. Above 1500mm in a door there is no need to toughen.

Why low iron?

 

[clewlowm]

as per the regs anything above 1500 is fine. but i see it as good practice to use tuff glazing in all areas of the door. the low iron glass can help to with the centre pain u value.

 

[RogerS]

.... the low iron glass can help to with the centre pain u value.

Hmmmm....this guy seems to think that that is debatable. Do you have any links to support the view that low iron glass is better than k-glass or Planitherm Total+, for example?

 

[dickm]

Asked my daughter (she's an engineer with Pilkingtons) about this and she passed the query on to their expert. Here's his reply:-

Low-iron glass transmits more Solar IR or Short Wave IR.
Pilkington K Glass™ reflects Far IR or Long Wave IR. These 2 functions are really not connected.

Tech Bulletins on our website explain these differences but who reads them? I simply say look at 2 numbers to compare window performance:

U-Factor (or U-Value) measures Thermal Conductivity. You ALWAYS want a low U-Factor and therefore you ALWAYS need a low-e coating which lowers U-Factor. If it’s cold outside you don’t want to lose heat by conduction. If it is hot (Dallas or Dubai) outside you don’t want to gain heat by conduction.

(On the rare occasion when it is cold outside but your room is too hot from too much sun through big, clear windows then yes you do lose the cooling effect of a bad window with a high U-Factor conducting that unwanted heat outwards, but the solution is very simple: open the window for free cooling).

SHGC (Solar Heat Gain Coef.) (a value from 0 to about 0.9) simply says how much heat (%) from the sun shining on a window ends up in the room. In summer we want low SHGC, or a shade to prevent sun directly reaching the glass, and in winter we want high SHGC for free passive solar heating. Therefore we need a switchable glass but currently at ~$100/sq.ft. the consumer is resisting. So we compromise. If your Heating bill is greater than your Air Conditioning bill then it’s typically better to have a high SHGC glass for residential buildings.

The English climate needs high SHGC, rather than low SHGC, for typical residential glazing, as does NA north of a line from Seattle to NYC.

We did a $300,000 study of all this at Nat. Res. Center, Ottawa, Canada. A summary is at:

http://index.nrc-cnrc.gc.ca/cgi-bin/sea ... cnrc.gc.ca

From what I can make out, low iron glass has a higher visible transmission, so lets in more light, but this doesn't affect the U-value, which refers to conduction of heat through the glass, not radiation.
Which glass to use, according to him, depends on the balance between need for heating and the need for air conditioning (the latter, in Aberdeen, of course, being nil )

So now we know