The great 'Double Glazing Con'

[RogerS]

Out of curiosity, I have been playing around with one of those online Energy Performance Certificate software packages. I was curious to know what difference it would make to the final EPC score switching between single and double glazing. (I stress that the figures are based on our house ...if your house is 100% glazed areas and no walls then YMMV).

It confirmed what I have long suspected, namely that this ridiculous push towards ever more daft u-values for windows by Building Control actually makes Sweet F*** All to the energy saving of the country. Not to mention the goddam ugly windows that need 6 x 2 glazing bars to take the dgu's (OK...I exaggerate a little but you get my drift?).

The difference in the EPC figure is 1. One. One point. Or as I prefer to call it 'pointless'.

Double-glazing is a con.

 

[bugbear]

The payback time of DG is well known to be very long. There are many, far more effective, ways of saving money
on your heating bills.

Here's a typical analysis.

http://www.telegraph.co.uk/lifestyle/in ... th-it.html

BugBear

 

[blackrodd]

I've No doubt you are correct in what you say, but after changing 17 windows in my 3,000 odd sq.ft house for D, Glazed windows in 2011, The difference in heating costs was incredible, and no more painting too!
How you can feed that into a computor programme, I'm not sure.
Regards Rodders.

 

[Phil Pascoe]

I was told I could jump a grade on the EPC by installing CFLs or LEDs in all fixed lighting. There were two that weren't already done. Ludicrous. The EU strikes again.
Edit - and that I could save £40 a year by installing under floor insulation. All the while ignoring 24 feet of uninsulated 4" block wall between the garage and the bungalow.

 

[doorframe]

I would suspect the savings would vary according to just how old and bad your windows are. When I moved into my house it was fitted with 'crittal' windows (is that spelt right...crittal?). With 10 windows in the front and plenty more in the back, the GCH was incapable of heating the house, and needed supplementing with electric. One electrical quarter like that was enough. Fitted DG as quick as possible and never looked back.

 

[Racers]

The pricing is the worst con, my mother was getting some quotes most came in at £3500 to £5000, until she has a well known TV advertised company come round and quote £23500 but they could offer 50% off.
I know why they use the highest mountain as the name, it reflects there price.

Pete

 

[Jacob]

I've No doubt you are correct in what you say, but after changing 17 windows in my 3,000 odd sq.ft house for D, Glazed windows in 2011, The difference in heating costs was incredible, and no more painting too!
How you can feed that into a computor programme, I'm not sure.
Regards Rodders.

To compare/contrast you'd need to give the actual figure saved on your heating costs and compare that to the cost of the windows and their devaluation - bearing in mind they often need units replacing from 5 years on and the complete replacement in 20 to 30 years.
You also need to consider the principle energy saving effect of DG units which in most old houses is the result of better draught proofing - which could be applied to existing windows.
I've been looking at it for years and decided a long time ago that replacement DG is a big waste of money and even for new build is dubious. There are plenty of better ways to save energy.

 

[RogerS]

I've No doubt you are correct in what you say, but after changing 17 windows in my 3,000 odd sq.ft house for D, Glazed windows in 2011, The difference in heating costs was incredible, and no more painting too!
How you can feed that into a computor programme, I'm not sure.
Regards Rodders.

That is exactly what I did to plug into the EPC software. I measured the sq m of each window, the compass facing direction and then was able to change the parameters from single to double to triple and variations in between. It WILL depend on the relative sizes of your own windows as I was at pains to stress in the OP. The total size of our windows is about 19 sq m for a 10 metre x 10 metre square two storey property.

 

[Phil Pascoe]

DG obviously does work - why else would Norway and Sweden (e.g.) use treble glazing? But the benefit depends on how cold it actually is outside - for most of the year it's not particularly cold. (Where I live 0c is positively arctic.) As Jacob says, most of the windows replaced didn't fit - if you replace an ill fitting metal framed single glazed window with a well fitting single glazed wooden one there'll be a **** of an improvement. I suspect for most people in towns the noise reduction is as important as any heat saving. I would however question the replacement time - I've had DG for 30yrs, and I've never had to so much as replace a panel.

 

[RogerS]

Triple glazing is much better, I agree. But double-glazing is, IMO, a waste of money as the payback period os light-years.

 

[bugbear]

Triple glazing is much better, I agree. But double-glazing is, IMO, a waste of money as the payback period os light-years.

You know light-years measure distance, right? :wink:

BugBear

 

[RogerS]

Triple glazing is much better, I agree. But double-glazing is, IMO, a waste of money as the payback period os light-years.

You know light-years measure distance, right? :wink:

BugBear

 

[zb1]

It's not the DGUs that are the problem it's the way EPCs are scored that is the issue, that and the prices peddled by some national installers.

Double glazing provides a greatly increased acoustic and thermal insulation values. A standard 4mm annealed glass sheet has a u value of u/5.8. the same double glazed unit with two sheets of 4mm and a 16mm spacer with 90% argon fill gives you u/2.6. Add a low emissive coat to the DGU and this falls to u/1.2. This not only decreases heat loss from the building but also helps to improve the internal atmosphere by reducing condensation and stabilising internal relative humidity.

The acoustic performance is also marked, especially if you have two different glass thicknesses making up the DGU.

On top of that DGUs are not really that expensive. 19m2 of 4-16-4 low-e argon fill should be in the region of £600 +VAT for the units. You should make that back in gas bills in 5-7 years depending on usage. (That article is from 2005 claiming £150-200 p/a, the price of gas has gone up about 10% since then.)

As for the 5 year replacement, 5 years is the minimum guarantee provided by most unit manufacturers. However the vast majority of units last much, much longer. 15-20 years is a better estimate of average life span. The reasons units fail is also much better understood now than it was 30 years ago. Units should be drained and vented so the hot melt used in the sealing process is never sat in water either through condensation or weathering. This is why the units are sat on packers and the frames should have drain holes. That goes for uPVC frames and wooden frames. On the subject of longevity the uPVC frames also have a limited life with UV degradation. If you have wooden windows that are well maintained the cost of replacing the units ever 20 years should be easily recoverable against the rising cost of gas.

Having said all that if your sales person manages to get someone to pay £12.5k then the payback will never really appear. I did the 9 windows in our house which equal approx 13m2 for less than £2k 3 years ago but I do have trade contacts for the uPVC frames and a glass merchant that gets a lot of custom from us.

 

[Jacob]

If you really need acoustic insulation then yes DG (diff thicknesses) is the way.
But DG doesn't necessarily do anything much for condensation - it all depends on a lot of details and you may just end up getting it somewhere else.
If condensation is a prob then ventilation control is a better and cheaper solution.
Next best is properly designed single glazing, ideally the traditional sash - condensation drains off at the meeting rail gap and the bottom sash and the window itself acts as a passive dehumidifier. Doesn't have to be a trad sash - there are plenty of ways of designing in this effect.
A rule of thumb for savings is that DG will take 5 to 10% off your bill - so on £1000 p.a. bill you save £100 a year. Bguger all really. Draught proofing and insulation will do a lot more. New windows usually means better draught proofing anyway.
The trouble with the regs is that they have been cobbled together with glazing manufacturers who have (surprise surprise!!) an interest in selling the stuff. They aren't interested in the alternatives.

 

[Lons]

Yep, I sit here in my comfortable draft and condensation free double glazed, centrally heated house and desperately long for the good old days when the condensation on the single glazed windows froze in the winter and had to be scraped off :wink:
I also don't know what to do with the time I've gained by not needing to paint or repair the windows and cills. All I have to worry about these days is whether to spend that time on the golf course or in the workshop. :roll:
I don't give a **** whether I get any potential savings back in 10, 20 years or never, I can't buy back that time.

I'd add that I agree about thieving conmen salesmen and that "A" mountain peak lot are a prize example. I fitted my own ( 22 windows plus doors) so was very cost effective as far as I'm concerned.

The most effective "radiator" I have btw is the conservatory, followed closely by the porch. A heat sink as soon as the sun comes out and helps keep the fabric of the house warm. My house is detached and exposed, is cavity wall insulated and 300mm in the loft but concrete floors I can do little about and we have an open fireplace which of course helps a lot with ventilation..
cheers
Bob

 

[Jacob]

not needing to paint or repair the windows and cills is possible if you stop using modern paints and go back to linseed:
http://www.oldhousestore.co.uk/allback- ... -555-p.asp
I've been using this stuff under the Holkham Hall label but I see it's now reverted to the source - Allback.
It's utterly brilliant - to use that is, it's a bit dull you don't get the high gloss of modern paints but it sticks like sh|t to a blanket. I don't use anything else now.

NB plastic windows aren't maintenance free - things break, wear out, distort. There's nothing magic about plastic and it's not easy to mend.

 

[blackrodd]

The very thought of paying £40, odd a litre and rubbing down and laddering and scaffolding to use it,
Not when I'm thinking of retiring sometime soon, I wan't time off!
Rodders

 

[Lons]

not needing to paint or repair the windows and cills is possible if you stop using modern paints and go back to linseed:
http://www.oldhousestore.co.uk/allback- ... -555-p.asp
I've been using this stuff under the Holkham Hall label but I see it's now reverted to the source - Allback.
It's utterly brilliant - to use that is, it's a bit dull you don't get the high gloss of modern paints but it sticks like sh|t to a blanket. I don't use anything else now.

NB plastic windows aren't maintenance free - things break, wear out, distort. There's nothing magic about plastic and it's not easy to mend.

Don't want to paint at all Jacob, you missed the point entirely and I'm old and experienced enough to have grown up with old formula paint :lol: You clearly like painting so keep up the good work, someone has to do it! :roll:

Where in my post did I say that PVCu windows are maintenance free? - Please read the posts properly!
They actually, providing you buy decent quality, are very low maintenance and the same applies to the sealed units. Life can be 15 to 20 years and I've seen longer. Breakages are often due to misuse similar to traditional windows.

How many have you actually fitted yourself to provide you with so much enlightenment btw?
cheers
Bob

 

[Jacob]

......
How many have you actually fitted yourself to provide you with so much enlightenment btw?
cheers
Bob

Several hundred sash windows period replica replacement and repair maintenance of several hundred more. Zero plastic windows. A couple of goes at DG in old sashes but decided it was a waste of time. And a lot of other woodworky stuff, conservation, building work and bits n bobs of furniture.
A never ending stream of enquiries ; what to do about failed DG units i.e. seals gone misted up inside and the impossibility of getting anyone to honour guarantees. They tend to imagine that they are just unlucky, not realising that it is extremely common. The ones that don't fail seem to be the lucky few.

Trad windows can last 100s of years. I'm strongly inclined to think that I wouldn't have been in business at all if it hadn't been for modern paint - stripping off the old linseed oil paint and replacing with modern is the kiss of death. Even new work suffers with modern paint. I'm about 7 years into linseed oil paints and the difference is astonishing. I wish I had known about it sooner.

 

[DennisCA]

I wonder if they had similar discussions in the late 1800s here when double glazing was becoming standard on houses.