Window glazing

[geoffreyroe]

We have a grade2 listed farmhouse, currently this has old 'closed casment' type victorian windows with single glazing (4mm a some 2mm glass)

I am hoping to replace the windows and while doing so plan to upgrade the glazing to 'low e' sealed units / i can keep the stlye of the window the same as the old with the only difference being the thicker glazing of the new sealed units.......

Although i have not as yet made a formal application to the listed buildings department, they do not sound to keen on the change (they mention using secondary glazing instead).

Does anybody have any similar experiance? My feeling is that with so much pressure to improve therma insulation it cannot be right to reinstall single 4mm glazing.

 

[middi]

You are stuck between the devil and the deep blue sea I'm afraid.

If the CO insists on single glazing that is what you have to do. You can certainly try nicely to persuading him/her to accept traditionally hand made ( but double glazed) windows.

There appears to be a shift towards double glazed units in some listed buildings. It all depends how the CO interprets the particular situation

 

[Flyfisher]

I agree with Middi. Your question might elicit a range of opinion here but, in reality, the person to talk to is your council conservation officer as they will be the decision maker. You said they did not seem keen; does this mean you've already discussed it with them and they've totally refused?

Also, what's the condition of the existing windows? If they are sound then it doesn't seem a good idea to rip them out, hence the suggestion of secondary glazing might be a good idea.

 

[Nemesis]

Why are you going to replace the windows at all? Sound conservation, assuming these are traditional windows, would be repair, and if they are too far gone (unlikely) then a like for like replacement a faithful copy.

Throwing away historic joinery and replacing wobbly glass with new and flat is rather against the spirit of why buildings are listed.

Consider instead draughtproofing (Ventrolla, DIY ), using stick-on film, and if the CO considers it suitable secondary glazing. Storm windows is fairly unobtrusive, but fitting secondary will depend on how much damage has to be done in the process.

Curtains help retain heat at night, although windows in period buildings tend to be small in many cases and heat loss here not really such a big deal.

 

[dandrew]

To be honest the idea of replacing windows to save energy is one put out by double glazing firms. A house looses about 10% of its heat via its windows. Double glazing will reduce this by half - so 5%. If you spend £1000 per year on heating (not unreasonable given rising energy costs) then you can save £50 per year on your heating bills. With a 10 year guarantee on your double glazing units you will save about £500 over the double glazing units lifetime. That will probably be enough to pay for 1 new window unit. Given that you will probably need at least half a dozen more windows it seems crackers to bother - you may as well put the money on the fire, at least you'll get the warmth from it as it burns.

 

[biffvernon]

Hmmm, just because something is guaranteed for 10 years, doesn't mean that after 10 years it falls apart. Double glazed units really should last very much longer (I've some that are 20 this year).

Energy-wise, it probably is worth replacing single for double glazing in many situations. The energy saving is pretty clear - but that does not mean there is a financial saving. That depends on the price of the new windows. From the financial point of view it is usually only worth changing to double glazing if the old windows have reached the end of their life and are being replaced anyway.

None of which alters our responsibility to care for our cultural heritage and not damage historic fabric.

 

[DaveBrigg]

We were in an identical situation, with the heat loss through the glass being insignificant in comparison with the icy winds that moved freely around the sashes. For just over £200 we bought online enough acrylic panels (cut to size) to cover each window. They are screwed to the frame, which has caused a little damage, although the screw holes can be easily filled. Between the acrylic and the frame I used draught excluder, like the stuff used for door frames.
This has made the rooms noticeably warmer, and with curtains hiding the edges, the acrylic is almost invisible. The only problem has been the acrylic expanding once it was fitted. I don't know why, because it is colder now, and it was fitted at room temperature. A few more screws straightened things out. The two thicker sheets used for the children's rooms were fine.

 

[skier-hughes]

Dave, maybe hotter with the heating on just below the window?

 

[DaveBrigg]

That may well have something to do with it.

 

[geoffreyroe]

Thanks for all your comments, most helpful

Just to answer a few points - these windows and there glazing are in very poor condition and in need of replacement, they have in the past been enlarged so there thermal impact on individual rooms is larger greater than normal.


Many thanks all...............................

 

[Raylea]

I have two huge single sash bay windows, all original and must admit I would not change them for anything and to be honest I wouldn't even add a secondary glazing to them I don't find them excessively draughty, they don't suffer with condensation and I always pull the curtains of a night. (They are to be admired not hidden.)

Raylea

 

[Nemesis]

Why Double Glazing is a waste of money
As a rule of thumb the average house loses 10% of its heat through the windows and Double Glazing will halve this to 5%. If the heating component of your fuel bill is say £500 per year then Double Glazing will save 5% of this, i.e. £25 per year. Double Glazing your home is likely to cost from £2000 to £5000 so there is no possibility of it being worthwhile as a money saver.

The position is made worse by the fact that Double Glazing units often fail within 20 years or so and then need replacing. Even if new windows are being fitted anyway, the extra cost of Double Glazing is not likely to save money.
Fitting Double Glazing to existing windows is even less viable, since in order to make the Double Glazing units fit an existing frame they have to be made with a smaller air gap which greatly reduces their insulation effectiveness.
If the existing windows are sashes then the increased weight of glass creates a sash weight problem - there may not be enough room for the larger weights required, which are an expensive item to replace anyway.
So Double Glazing is usually a waste of money however you look at it.

Details vary - there are some circumstances where Double Glazing will save money, e.g. where there is high exposure to wind - tall buildings, high altitudes etc. You can verify the details yourself with one of the many DIY reference books, or a competent heating-engineer or central-heating installer is able to calculate accurate figures for a particular building - but don't ask a Double Glazing sales-person!
Alternatives to Double Glazing
The good news is that there are plenty of other ways to reduce heat loss which are also likely to save money. The simplest and most cost effective is to turn down the thermostat by a degree or more and to turn off radiators when rooms are un-used. Other methods involve expenditure which will eventually be recouped after a number of years.

These are–
Loft insulation
Cavity wall insulation
Replacing an older boiler with a modern high-efficiency boiler, especially a condensing gas boiler
Fitting and using thermostatic heating controls
Reducing draughts
Using low-energy light bulbs
Fitting roller blinds and/or thick curtains
If you really want to spend your money then consider solar heating, - systems are improving and becoming more cost-effective by the day.
Bath with a friend etc.
If all these things are done then the proportion of heat lost through the windows will be much higher, but the saving due to Double Glazing will be a bigger percentage of a smaller heating bill, i.e. the same - still not worth doing.
But isn't saving energy by double glazing still a benefit to the environment even if it saves no money?
The answer is almost always NO. The energy consumed in marketing, making, fitting etc. is much greater than any saving.

http://www.owdman.co.uk/joinery/notes.html#dp

The undesirability of double glazing
It is impossible to double glaze a traditional sash window without spoiling its appearance, due to the deep rebates and larger sections of glazing bars demanded by double glazed units. A double glazed sash is very heavy and hard to move, and requires bead glazing which is ugly and not durable compared to putty. Double glazed units tend to fail - they are dependant on an adhesive seal around the edge and these eventually become brittle and fail, allowing moisture into the cavity and so needing replacing.
Why build in obsolescence? There are energy saving alternatives to double glazing (see PAGE 2)

The combination of double glazing and draught sealing create a problem, particularly in old buildings - humidity levels are kept high causing condensation problems such as damp mouldy patches on walls. Single glazed windows function as de-humidifiers - allowing condensation to collect and drain off to the outside.

 

[Moo]

Single glazed windows function as de-humidifiers - allowing condensation to collect and drain off to the outside.

How does this happen? In my house the condensation always drains off to the inside of the windows.

 

[biffvernon]

This works when the sill becomes so rotten that the water can flow out through it

 

[Nemesis]

It vanishes very rapidy in our bathroom, when the sash is opened slightly to allow some air.

 

[Moo]

The other bit I found interesting was the inclusion, in the list of "ways to reduce heat loss", of low-energy light bulbs.

One learns something new every day.

 

[skier-hughes]

Low energy bulbs produce less heat, thus less heat to lose.....

 

[Moo]

Er............... ?

 

[Penners]

This works when the sill becomes so rotten that the water can flow out through it

Ain't science amazing?

 

[Penners]

Low energy bulbs produce less heat, thus less heat to lose.....

Hmmm - are you sure?

If your house is centrally heated, then it will almost certainly have a thermostat that cuts out the boiler when the house has reached your chosen temperature.

The thermostat isn't fussy about where the heat comes from - radiators, light bulbs... only that the chosen temperature is reached.

So if your light bulbs give off less heat, your boiler needs to give off more heat.