Secondary Glazing Advice

macleanmhl

Hi I am considering putting some secondary glazing on my timber framed single paned windows. Most DIY products i see are attached to the outer frame. However when i look into best practice is sounds like the secondary glazing should be between 100mm and 200mm max away from the existing glass for the best heat insulation. If i install on my window frame it will be 4-5 cm away from the glass.

Will this distance reduce the insulation effect dramatically? Is is possible to put the secondary glazing closer to the glass (perhaps by putting an inner frame directly against the glass? )

DaftyDuck

I've built my own secondary glazing a few times now, and am about to embark on it again.

The gap between the sheets appears less important in secondary glazing than modern double glazing. I have never gone as much as 100mm, for sure no further. Mine has always been (a variation on) strips of hardwood frame routed or even sawn with a channel for the glass, normally fixed to the outer window surround. So, with sash windwos, my frame fits against the fixed surround, not the sliding sash, and with swing openers it fits to the surround, not the opener itself. I use wood size to match the original frame wood, so the distance from the glass to glass will vary, but I guess it's in the 3 - 5cm range.

It makes a huge difference, not least from sealing draughts. However, the thermal efficiency is, from a detailed house heat survey, up with ordinary "modern" 1970's and 80's double glazed windows. I was told it's the frames of the older double glazing that are as much to blame as the glazing. The glazing rating is, in my opinion, a load of pants, as it varies with solar loading, thermal loss, who wins X Factor, and your star sign.

I haven't used any special glass previously. I am going to consider if any of the low "E" glass is appropriate, and a friendly double-glazing bloke has offered to give me a skinny double glazed unit to play with, to see if I can make use of that. Yes, give! He might get the job of fitting a large conservatory, but there's no certainty. I can see the extra rigidity and strength may pay dividends.

Frankly, I have found such success from simply adding secondary panes that I'm happy with that. Draught proofing and the thermal air layer seem to do wonders.

Condensation between the glass has sometimes been a problem (solved by better sealing. Complete removal for summer (and storage where?) has been the other. It's worth careful thought & construction to make a frame that seals well, opens, and can remain in situ all year.

Grenage

Ahoy, Daffy.

Any reason you didn't opt for swapping the panes out with double, rather than adding secondary?

DaftyDuck

Ahoy hoy...

Well, mainly because I'm a lazy something! Or, because the windows themselves have always been old , and I don't want to lose what's there. Where I am now, most of the glass is Victorian cylinder glass, bubbly, and slightly tinted. Where I have had to put in occasional (single-glazed) replacement panes stand out by their clarity. Where I have put in removable secondaries, realistically they can be stored in the attic for nine months of the year . Where I have put swing frames in, another punter could remove them entirely and, aside from four screw holes, there'd be no sign of any change.

If I were replacing single-glazed panes from the sixties, I'd probably put in double panes, or simply replace the windows entirely (but not expecting a return on the investment through heat savings). This house I'm now in has lovely Georgian sash windows, the earlier ones had original Victorian openers, and the one before those had proper medieval mullion windows in part, so they were staying as they were.

Secondary double glazing, if done well (and I'm not sure my DIY stuff counts) can look really elegant, and I believe it can make as significant difference to thermal efficiency as upper-end uPVC double glazing.

It costs a tenth as much to install! I reckon around £20 - £40 per metre-square window.

Grenage

Cheers! I was curious as we've bought a place with a handful of original windows, and while most have had the panes replaced, they're very thin. I was toying with the idea of swapping the panes out in summer, and I hadn't given secondary any though.