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I feel a need for clarity where windows are concerned.
First let me emphasise that it is always better to repair than replace, and second that I really hate plastic windows. Some folk who agree with those two points equate double glazing with plastic windows and others, who acknowledge the existence of double glazing in wooden frames still associate double glazing with a lot of bad things to do with other aspects of the window.
Double glazing means that there are two sheets of glass. It usually, but not necessarily, involves a sealed unit. These have two serious defects. Firstly, they might last only a very short time, before becoming unsealed and steaming up or they might last many years, but they won’t last forever. When they fail there’s probably nothing to do but throw them away. Careful installation can increase the likelihood of a relatively long life. Secondly, they require a wide glazing bar, at least 36mm, to hide the black mastic that holds the unit together.
Double glazing has got nothing to do with how draughty a window is. That depends on how well the sashes fit their frames and what, if any, draught excluders are fitted. You can have draughty double glazed windows if you want to.
Double glazing does eliminate condensation on the inside of your windows. When you get up on a cold morning you can see out. You don’t get puddles of water collecting on the inside of the window frames where the condensation has run down. You miss out on the beauty of ice flowers in frosty weather.
Double glazing does reduce the heat loss from your house. The energy saved, if you keep room temperatures the same, is much greater than the embodied energy used in the manufacture of the extra sheet of glass. In practice, human nature being what it is, a change to double glazing may result in warmer rooms and less woolly jumpers rather than a fuel saving. That’s a lifestyle choice made available by double glazing.
Double glazing does reduce the noise coming in very significantly. It’s true that the ideal spacing for heat insulation of about 16mm is less than the ideal for sound, but, nevertheless, double glazing with a 16mm gap makes a real difference to the quality of life for people living near busy streets.
Glazing bar thickness is a matter of historical fashions and aesthetics. We have become very used to the thin bars associated with Georgian and Victorian design, often with a thickness of 20 or 18mm, sometimes even less. Older houses, Queen Ann and before, often had much wider glazing bars, as did many humble cottages of a later date.
20th Century fashion dictates that windows are painted white. In earlier times dark colours were more common. White shows up the glazing bars much more than dark paint or unpainted timber.
In previous centuries, glass was very expensive, folk were hardier and did not worry about global warming or the impending global fuel crisis. Single glazing was appropriate. Today we have grown used to our creature comforts, global warming is the biggest crisis facing humanity and after oil production peaks, probably sooner than most people imagine, energy prices will change everything. At present, glass is cheaper in real terms than ever before. The glass is a small part of the cost of a conventional newly built house.
Preserving our finite resource of historic fabric is critical. The good maintenance and timely repair of historic windows is our responsibility. When the original fabric is decayed beyond repair or has already been replaced it may be appropriate to recreate replicas of the historic design for the sake of appearance and historic integrity of a building. But this is not always the case. Buildings do develop through time and while it can be important to conserve, like museum specimens frozen in time, it should also be acknowledged that what we now have is the result of evolution. An old house may show bricked up windows, the result of taxes, windows divided into small panes from the time when glass could not be made in large sheets and large single pane sashes dating from prosperous Victorian times. The windows, though forming a pastiche, are aesthetically pleasing. They are the result of good design, craftsmanship and appropriately sustainable materials and techniques.
A great part of the British housing stock comprises 18th, 19th and early 20th century buildings that are not listed, not in conservation areas and do not have the particular historic significance that warrants listing as things stand. And yet they deserve better than to be despoiled by poorly designed materials using unsustainable materials and methods. Foremost amongst these must be plastic frames but timber windows cannot escape criticism when made of tropical hardwoods or non-durable softwoods soaked in biocidal chemicals and finished with alkyd paints. The non-uniform glazing lines found on many modern casement windows are aesthetically offensive to some eyes.
The challenge today is to offer an alternative to plastic and to bad design, materials and workmanship. We need to make windows that provide high levels of comfort and ease of maintenance, are environmentally and aesthetically sound, and can be installed in period buildings without compromising their integrity.
Double (or triple) glazing does not have to be factory made sealed units. Glazing bars can be as thin as were ever made in the 19th century. Glass does not have to be float; mouth blown cylinder glass is available and can be used in double glazed windows. Exterior wood does not have to be painted white. It does not have to be painted at all.
Ventilation is a subject quite independent from double glazing.
Next century someone ought to be able to look at an old house and identify its stages of development over several centuries, including this one, and see that at each stage something of lasting value was contributed.
One long lasting contribution of the late 20th century will be large quantities of UPVC, that made before 2003 identifiable by its heavy metal content of lead and cadmium or, in newer material, tin. Later UPVC will be identified by its less poisonous content of zinc. That’s progress.
Lincolnshire
©Biff Vernon 2005