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Low-E glass, conflicting advice.


Jenni

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Hello. 

I'm worried about solar gain making my barn conversion uncomfortably hot as the majority of my windows face SSW, to what will be the rear garden. 

 

One glazing company has said that low-e glazing will help, but another has said it won't. I've found similar contradictions searching for an answer online. 

 

Can anyone help me figure it out please? 

Thanks. 

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Low emissivity glass is usually fitted as one (or two in triple glazing) coated panes within the glazing unit, arranged to reflect heat back into the house, so keeping it warm.  If you want to cut down the amount of heat getting in, then the glass needs to have a heat reflecting coating or treatment on the outside, so reflect heat outwards.  It is possible to specify glass that has a low inward heat transmission, but until relatively recently it's mainly been used for commercial applications, like big glazed office blocks, as a way to reduce the air conditioning demand.  It's definitely a special as far as most window companies are concerned, so needs to be specified carefully, and may well attract a price premium.

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I have low e coating on my 3g windows, suspect most high u value windows have this as a standard feature all designed to keep heat in.  I have an overheating problem. My large glazed areas are s & sw facing, at design stage I asked about bris soleil but was told didnt need ..I clearly need something.  I have deepish overhangs but not deep enough to shade properly.  We had engineering issues with loading and wind due our high exposed location so they are as deep as was practical.

 

I have had solar film fitted to try and help but until next summer I wont know how much benefit it will be, it didnt go on until October. I have the pleated blinds as well as film in bedroom areas. The living area glazing has no blinds.

 

In my experience overheating can be a problem in some highly insulated houses as they hold the heat.  In an older house with 2g south facing glazing it was much less of a problem. How well insulated is your barn going to be?  It can be hard to get those old buildings up to the standards of a modern construction in which case you might welcome the extra warmth e coating gives and consider some coating/film/blinds for shading in the summer.  You can get windows with integrated blinds too or very nice external blinds but they are very expensive.

 

 

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Thank you both.

 

So low-e is designed to keep heat in, not out, and therefor won't help reduce any solar gain. The glazing companies I've spoken to so far about my concerns haven't mentioned availability of glass that has a low inward heat transmission, so I suspect it's not on their radar.

 

The build is only going to be double glazed, with insulation to current reg's, or a little better. Low-e glazing is specified as required, so will have it. 

 

Looks like I'll have to go the route of film if it's required, especially if it's possible to get one that's not too 'silvery'.

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So.... you could go for triple glazed and flip the middle pane so you get the reflective coating on the outer side... and then keep the Low-E on the inner as normal. 

 

@craig isn’t there a St Gobain standard for this ..??

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I'm pretty sure there is a commercial glazing unit that's like this, as we fitted them to the new lab/office building as part of the last job I managed.  I remember it because the construction crew fitted roughly half the glass panes the wrong way around, and the next morning when the sun came out it was very obvious from outside which panes were not reflecting and which were, as the colour looked very different (they blamed Eastern European workers who hadn't read the labels on the glass - not fair IMHO, as the chap overseeing the job should have checked).  Cost SRM a fair bit, as there were a hundred or so glazing units, around 2.5m x 1.5m, that had to be changed.

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@PeterW   would be interested to know if there is a 'standard' offering, (I may be mistaken, but think this would be more affordable than a bespoke spec).

 

A friend of a friend had some windows replaced last year and said the solar gain was much reduced compared to his old units, when I asked him for the spec he replied - clear tough low e / thermobar / Argon. --- would the Argon fill make the difference to solar gain? 

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well, this is from IdealCombi's glass guide;

"Solar reflective glass

Solar reflective glass reduces the amount of thermal energy and/or light which is admitted through the unit. This type of glass is often used for large surfaces where the aim is to make full use of the sun- light while at the same time keeping out the solar heat. In other cases both the sun and the heat is kept out."

 

It's on this basis that I specced it in some of my windows...which when I stand in front of I can appreciate a distinct difference so i'd say it works.  To my recollection it added approx £300 to  one of my typical 1.5 x 2.3 units(but my memory is a sieve).

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