Double or single glaze door?

[Doug71]

A customer wants a new front door making, it's about 36" wide, 80" high and 1.75" thick.

Main house is a lovely big old farmhouse with single glazed sliding sash windows which have very fine glazing bars. They had a large extension on the back of house a few years ago which is all double glazed.

The old front door was a solid 6 panel but the new one wants glass in the top (9 small panes) to let more light into the entrance hall and 2 solid panels in the bottom, there is also a glazed light above the door to replace.

They are talking about wanting it double glazed but this will mean stuck on bars and think the thinnest units my supplier does with the multi spacer bars inside are 18mm which wont leave much for the mouldings front and back, also it will probably be aluminium spacers at that thickness.

Never used the slimlite type units and think the cost would put them out of the equation.

I would quite like them to keep it all traditional and have a single glazed door, think it would be more in keeping. The old part of the house is all single glazed (original thin old glass) and solid brick wall so not very thermally efficient anyway.

Anybody got any good points/opinions/views either way to swing the decision?

Thanks in advance, Doug

 

[Jacob]

There would be zero cost benefit with such a small area. Less than zero in fact, double glazing does not pay for itself in any situation.
It sounds like one of those "just say no" jobs. Do them a favour!
Remember rule 1; "The customer is always wrong"
More effective and much cheaper would be a heavy curtain - they also damp down drafts very well.

 

[MikeG.]

......double glazing does not pay for itself in any situation........

Oh Jacob, please. That's pure nonsense.

-

To the OP.....is the building listed? If so, this isn't a decision for them or for you, but for the Listed Building's department at the council. Some councils are now allowing double glazing in new extensions to listed buildings, but no-one allows double glazing in the original building.

 

[Jacob]

......double glazing does not pay for itself in any situation........

Oh Jacob, please. That's pure nonsense.
......

Do a bit of googling "is DG cost effective?" etc and find out for yourself.
Start here? https://www.which.co.uk/reviews/double- ... s-answered
DG is effective but not cost effective. A £100 p.a. saving on a £3 to 6k outlay is not cost effective, even less so when you look at obsolescence - most DG units fail in 20 years or less.
Thick curtains are much better value!

 

[thomashenry]

Sounds like DG would be a travesty in this scenario.

 

[MikeG.]

......double glazing does not pay for itself in any situation........

Oh Jacob, please. That's pure nonsense.
......

Do a bit of googling "is DG cost effective?" etc and find out for yourself.
Start here? https://www.which.co.uk/reviews/double- ... s-answered
DG is effective but not cost effective. A £100 p.a. saving on a £3 to 6k outlay is not cost effective, even less so when you look at obsolescence - most DG units fail in 20 years or less.
Thick curtains are much better value!

Well of course if you calculate it in the most bizarre way possible, you'll come up with a bizarre result. Here's the sensible way: cost of new double glazed window minus the cost of new single glazed window divided by the cost of borrowing the difference on your mortgage, subtracted from the annual saving on your heating bill.

Please tell me my triple glazing isn't cost effective. I'm dying for that conversation. My £70 to £100 annual heating bill versus your prejudice. Could be a fun conversation.

 

[Jacob]

......

Oh Jacob, please. That's pure nonsense.
......

Do a bit of googling "is DG cost effective?" etc and find out for yourself.
Start here? https://www.which.co.uk/reviews/double- ... s-answered
DG is effective but not cost effective. A £100 p.a. saving on a £3 to 6k outlay is not cost effective, even less so when you look at obsolescence - most DG units fail in 20 years or less.
Thick curtains are much better value!

Well of course if you calculate it in the most bizarre way possible, you'll come up with a bizarre result. Here's the sensible way: cost of new double glazed window minus the cost of new single glazed window divided by the cost of borrowing the difference on your mortgage, subtracted from the annual saving on your heating bill.

Please tell me my triple glazing isn't cost effective. I'm dying for that conversation. My £70 to £100 annual heating bill versus your prejudice. Could be a fun conversation.

Do you really get a £70 to £100 annual heating bill? I'd imagine it wouldn't be obtainable without mega insulation throughout, plus heat exchangers, with DG as a small component.
Typical heat loss through single glazing is 18% (it says). DG halves this to 9%.
Typical heating bill say £600 x 9%= £54 saving per annum. Not a lot.
Mortgage rates about 5%. DG installation say £5k, cost £250 per annum interest only - doesn't include replacement at 25 years.
£5000 mortgage at 5% takes 36 years to pay off (on line calculator) at £25 per month!! Your windows wont last that long, even if you do!
£25 a month is £300 a year but only saves £54 p.a.
n.b. No dog in the fight I'm just going by the figures! Could be wrong?

 

[doctor Bob]

Mike I suspect you are not allowing for the Northern element, eggy thump and all that. Jacob just puts his hat on and a pair of wellies when it's chilly.

Bobble hat, tweed jacket and wellies bought from a charity shop once every 15 years is far more cost effective than triple glazing.

 

[MikeG.]

.......Do you really get a £70 to £100 annual heating bill? I'd imagine it wouldn't be obtainable without mega insulation throughout, plus heat exchangers, with DG as a small component......

Not DG, but TG. But yes, that's what heating this big 300 year old house costs*, and yes, that's how it is achieved (plus judicious use of thermal mass, solar gain, and "airlocks" over the external doors), albeit there is only one heat exchanger. The windows have to come along with the rest of the thermal envelope otherwise there is no point doing the insulation etc.

*It costs approx 4 times as much to heat the hot water as it does to heat the house.

 

[MikeG.]

Mike I suspect you are not allowing for the Northern element, eggy thump and all that. Jacob just puts his hat on and a pair of wellies when it's chilly.

Bobble hat, tweed jacket and wellies bought from a charity shop once every 15 years is far more cost effective than triple glazing.

=D> =D> :lol: :lol: :lol: Precisely how I'll picture Jacob from now on.

 

[MikeG.]

....... DG installation say £5k......... Could be wrong?

Yep, you're wrong. You've failed to subtract the cost of single glazing from this. You are making the argument that replacing single glazing with double glazing isn't cost effective, but are failing to account for the fact that replacing the single glazing with single glazing would cost a pretty penny too. To do an honest comparison, you should be looking only at the price differential between double glazing and single glazing. The extra-over cost. If that comes in a a few hundred pounds, as it would at the worst case, then your argument doesn't hold quite so much water.

 

[Jacob]

..... The windows have to come along with the rest of the thermal envelope otherwise there is no point doing the insulation etc......

Actually not quite so simple. The heat loss through the windows and the reduction due to triple glazing remains the same whatever else is going on in the house, given the same temp differentials. i.e. the same saving, but a larger percentage of a smaller total. Still not a lot and almost certainly not cost effective, TG being much more expensive, unless you are up a mountain near the arctic circle! Do the calcs if you don't believe me! It's a common misunderstanding.

 

[Jacob]

....... DG installation say £5k......... Could be wrong?

Yep, you're wrong. You've failed to subtract the cost of single glazing from this. You are making the argument that replacing single glazing with double glazing isn't cost effective, but are failing to account for the fact that replacing the single glazing with single glazing would cost a pretty penny too. To do an honest comparison, you should be looking only at the price differential between double glazing and single glazing. The extra-over cost. If that comes in a a few hundred pounds, as it would at the worst case, then your argument doesn't hold quite so much water.

Only true if you can be sure of low obsolescence and not having to replace them in 25 years or so. Single glazing can be kept going for ever, with routine maintenance.
Basically DG can only save a small amount. Probably more gained by efficient draught proofing.

 

[MikeG.]

...... Probably more gained by efficient draught proofing.

At last you've said something logical.

Oh, and I've done the calculations. I'm an architect. Designing low energy buildings is what I do. You are fundamentally failing to understand that all your errors stem from the nonsense of counting single glazed windows as free. You haven't yet addressed the necessity to cost in windows of any description, and then subtract that from the cost of double glazed windows. It is the price difference we should be talking about, not the total price.........unless of course you are advocating not having any windows at all.

 

[Trevanion]

I would definitely go for single glazed on the door if you haven't got the meat in the door to take a decent sized unit, especially if all the other windows already are single glazed. You will have to go for toughened panes in a door though because of building regs and general safety, just keep that in mind.

Been doing a job lately taking some 12ish-year-old single glazed sashes out of a building and taking the 4mm panes out and replacing them with 12mm Krypton DG units. It's costing about £50 a piece for about a 400mm x 600mm unit, with 4 units in one box and another couple of hours of work ripping out the old putty (Recent putty is a nightmare to remove, it's good stuff.) and cleaning the rebate and taking it a little deeper for the unit. Then the boxes have to have the old cast iron weights removed (I guess they had some lying around and decided to use them up) and replaced with lead ones to make up for the extra weight. All in all, it's costing about £350-400 per box to redo, which in my opinion is pointless and expensive but ye must do what ye told.

Some councils are now allowing double glazing in new extensions to listed buildings, but no-one allows double glazing in the original building.

This isn't technically correct anymore, or at least out this way it isn't. I've done a lot of new windows in the national park and in the local towns on listed buildings and they've been very lenient on double glazing as of late, so long as it isn't the 28mm stuff and the window doesn't look much different they don't seem to mind. Might be different in other counties though.

 

[MikeG.]

...Only true if you can be sure of low obsolescence and not having to replace them in 25 years or so. Single glazing can be kept going for ever, with routine maintenance.......

You're confusing windows with glazing now. Come on Jacob, try to be clear thinking and precise. DG units fail......you don't then chuck out the entire window. You just replace the DG units. The triple glazed windows I fitted to a house I built in 1996, 23 years ago, are all 100%. It isn't inevitable that sealed units fail. Look out, too, for vacuum units, coming sometime soon.

 

[MikeG.]

........replacing them with 12mm Krypton DG units.........

These have a very poor reputation for failure, I'm afraid. I haven't specified any for ten years now, I reckon, because too many fail, and fail quickly.

 

[Jacob]

...... Probably more gained by efficient draught proofing.

At last you've said something logical.

Oh, and I've done the calculations. I'm an architect. Designing low energy buildings is what I do. You are fundamentally failing to understand that all your errors stem from the nonsense of counting single glazed windows as free. You haven't yet addressed the necessity to cost in windows of any description, and then subtract that from the cost of double glazed windows. It is the price difference we should be talking about, not the total price.........unless of course you are advocating not having any windows at all.

I've done the calculations too, on several projects. I've also looked at the web and other comments. It seems to be widely agreed that almost every other energy use reducing measure is more cost effective than DG.
I take you do accept that replacing existing single glazed with DG is not cost effective?
New DG as alternative to new SG is more difficult due to obsolescence of DG but I reckon the cost advantages are still marginal to negative.
If energy prices rise massively, as they should, given climate change, then all calcs are out of the window!

 

[doctor Bob]

Oh, and I've done the calculations. I'm an architect. Designing low energy buildings is what I do.

I'm afraid this counts for nothing with Jacob, he has googled it and read around a bit and knows better.
20 odd years designing low energy buildings, pah..........

 

[Rorschach]

Green building advisers in the US are predicting energy to get cheaper in the long term. There will still be rises for a while but once the shift to renewables takes hold and market forces kick in then the cost of energy will go down and insulation will be less important. People seem to forget there is a massive environmental impact in producing most forms of insulation.