advice on new sash window (make vs buy)

[jungle_jim01]

Hello again. I've got a hash of a window in the gable end. the original has been removed at some point, the space partly bricked up and a slightly smaller window installed which is now rotting badly. I'm planning on removing the whole window and knocking back to the original size. The lintel and sill are still in place so i don't anticipate this being a problem. But i'd like to replace with a sash window in keeping with the rest of the property. Ideally i'd like to make this myself but as usual i'm coming across the typical 'nanny state' regulations (quote from Box Sash window company):

"NEW -Tougher Government Glazing Regulations
All new or replacement windows must comply with the Government's new tougher heat retention regulations, Window Energy Ratings (WER). All new or replacement sash windows and hinged windows have to be manufactured to meet the new, higher demands on insulation, giving you more warmth and comfort as well as better heating economy. In fact, it means that, unless it is a listed building, the new or replacement windows have to be double glazed to this new standard, whether or not they were before.
Window manufacturers products are tested and accredited for compliance by the British Fenestration Registration Council."

This sounds like a bit of a nightmare if i want to build and install my own windows. Does anyone have any experience or advice about this?

Thanks again.

 

[MdB]

cough....

Build your window, install it, don't tell anyone....

... cough.

 

[worms]

But if you are building from scratch why would you not want to fit it with a double glazed unit? If need be, you can get units with very narrow gap and shallow spacers, so that it shouldn't make the fitting too clumsy.

Look up slimlite

Although these guys are in Edinburgh, similar products are available in the South and a Google search will give you other companies.

 

[biffvernon]

Yes but does anybody think slimlite are any good?

Jungle Jim, it's quite possible to make and fit your own windows and the easiest way to meet buildings regs is to use 4/16/4 argon fill low-e units - you just need to design your window so that it can take a 24mm unit. That means a 40mm rebate by the time you've added in the glazing tapes and beading.

 

[worms]

Biff,

I have no experience of Slimlite, but I find the concept interesting. If the technology for a smaller seal depth can work, then that is surely good news for making/repairing softwood windows, improving the thermal efficiency without changing the appearance?

 

[Penners]

I'm interested to know how the science of double-glazing works. I confess that my understanding of it has always been hazy, at best.

Firstly, if the gap between the two panes of glass were a vacuum, I could understand that no heat could be convected across from one pane to the other. I suppose there could be a small amount of radiated heat transferred from one to the other, but I guess that's why DG is not 100% effective.

But, if I understand it correctly, the gap isn't a vacuum - it's filled with an inert gas. Does this mean the gas (argon?) is unable to act as a heat convection medium? Is that why it's called "inert"?

But why go to all this trouble when air itself is a good insulator? Would DG not work effectively if the gap were filled with still air?

Secondly, as I've heard it, for thermal insulation a wide gap is better than a narrow gap, and for acoustic insulation a really wide gap is necessary, with the gap lined with acoustically absorbent material.

Why does the width of the gap make a difference? If heat (or sound) is not being convected across it, why does its width matter?

 

[biffvernon]

I think there were some experiments in Japan with vacuum units but they were not good. The external air pressure tends to bend or break the glass. Or they leak.

So all dg units are gas filled. Insulation increases with size of gap until it's big enough for convection currents to form. This happens around 20mm so you don't want a bigger gap than that (unless your goal is sound insulation). The insulation/distance graph is a sort of bell shape so in practice there's not much gain after about 16mm so this is the preferred gap,

Argon is used as a fill as it is a better insulator than air and is very cheap.

For very thin gaps, such as used in 'Slimlite' either xenon or krypton are used as these give better insulation in small gaps. But they are much more expensive. They are quite rare elements, whereas argon is very abundant.

 

[Andrew Bodenham]

Jim,

I'm just about to fit some new sash windows which I have made myself, after failing to find anything commercially that I liked the look of.

I drew up some design details and submitted these with a building notice to the local planning authority, who then issued a formal approval for the design and the work to take place. I'd had a useful informal chat with one of the building control officers first.

I've used 4/12/4 argon filled units, with so called 'thermix' spacer bars - these were chosen for aesthetic reasons as they are almost white and have very discreet perforations. From a distance the units could almost pass for single glazing.

I'm fitting the first one next week so I'll post some pictures.

 

[biffvernon]

Interesting that a 12mm argon gap unit got approval as the centre pane U-value is not going to be as low as the usually required.

 

[Joiner]

Actually Bif, don't forget that until October you'll still get away with...

http://i38.tinypic.com/33z7evt.jpg

On the old Pilkington Spectrum calculator a 4/6/4 gas-filled unit came out at 1.9, but not on this new version!

A while back my glazier reported that a lot of unit manufacturers started to refuse to make 14mm gas-filled units because they were such a fiddle, moving instead to a 16mm (4/8/4) gas-filled unit because it was easier to drill the charging hole - those that would still make them wouldn't guarantee them. I've used the 16mm size for about a year now without problem.

As for Slimlite, whilst at first excited by the idea, my initial enthusiasm was tempered somewhat by the bad reports I've had from the two guys I've spoken to who've used them, not helped by Slimlite's failure to respond to enquiries regarding the forthcoming changes to Part L. They are also horrendously expensive.