Function, Construction and Form of Windows

Since thousands of years windows are used in architecture. Alabaster, glimmer, textiles or thin skins have been used instead of glass. Nevertheless the construction of these windows was very similar. Even early Egyptian house models and relieves are proofs for such windows. Very often representations of Greece or Roman architecture show windows with four square sections - just as in our time.

Window means "wind eye", not only in the English language but also in most other languages as, for example, in the old German language "auga tora", or in the Scandinavian "vind-auga" and the slavic "oko" or the russian "okno". On the other hand, we are speaking about the facade as the face of a building. Houses are like a third skin for human beings.

The English word "face" has an etymological connection to "facade". In most Maya languages the word for door means "mouth". This also means that the facade of a house is its face consisting of mouth, eyes etc. and that there is a close connection between the eyes of a face and the windows of a facade. The eyes are the most expressive part of a face. The same applies to the windows of the facade.

Besides this, the window is the only part of a facade which you may see not only from the outside, but also from inside. So there is both individual and public interest in the form or function of this architectural element.

The window is determined by several criteria:

· to protect the inside of a room against wind, rain, cold, noise, animals, strangers, and burglars,
· to allow the exchange of air between inside and outside by opening the window,
· to allow light to get into the room from outside by transparent or translucent window panes,
· to permit communication with people passing by.

In many cases it should be possible:

· to darken the window by venetian blinds or roller shutters,
· to protect the window against mosquitoes.

Presently we have the greatest problems with the protection against growing noise and the growing need to save energy by better insulated windows, and we thus try to find the right windows for historic buildings. Testing old and new windows revealed that the best protection against noise is achieved by double windows - one behind the other - at a short distance of approximately 10 to 30 cm as was done in the 19th century. Such windows are usually more effective than modern industrial windows - this is even true for modern special noise-protection windows with 2, 3 or 4 panes within one laminated glass. You may find quite a lot of such double-windows in town quarters of the historistic period. These double windows are also quite good against the escape of heat, and they are typical for historic buildings.

In former times and especially in the futuristic period the window was a very important architectural element. It was accentuated by surrounding facade elements, consisting mainly of stucco, bricks and plaster, sometimes of wood. Most of these ornaments come from former functional architectural elements, for example, the small columns with capitals at both sides of the window, balusters in the parapet below the window or from roof forms above the window, like the segment bows with a key stone or triangular field, the tympanum for the protection of the horizontal stone lintel against static problems (see Fig. 4).
The window itself consists of the fixed window frame construction, the casements and the glass panes. In former times the fixed construction often consisted of stone elements producing the inner face of the wall opening, the reveal, and the abutment. This was true for windows until the Gothic and Renaissance period. Such stones were often richly ornamented. Later, this part of the window was usually constructed of wood. The transom is an element of the window which divides optically above all the wall opening when plane panes of glass could be produced in small size only. today such wooden dividing elements are not necessary anymore for the construction of a window.
Besides this, there are Venetian blinds and often very richly decorated lattices at windows on the ground floor.

As already mentioned - the form of the window is always part of the design of the whole facade to which it belongs. Therefore you will find very similar ornaments within the construction of the windows and in the rest of the facade. Even today good modern architecture shows relationship between facade and window, as for example similar proportions, similar sizes or divisions of windows and facade. Older windows usually show ornaments of the time of their construction, such as small columns of wood in their middle axis quite similar to those of the surrounding facade or window-mouldings with a similar profile to the cornices of the facade.

In the past partly rotten windows were usually repaired. So there was a continuation in the form of the windows, and hardly ever was there a rough chance in former times as today, caused by the complete change of all windows at once.

If there was a change of windows in the past usually the whole facade was renewed. So the facade of an old building is not always of the same time as the building itself. Windows changed their appearance with the development of new techniques to produce plane glass panes and this in combination with the architectural style.
During the last 40 or 50 years, little has been done to facades or windows. But even if a facade and its windows are older than 100 years, the substance of the windows is often better than their skin, which may look awful. To adept the windows of an old facade to modern standard there are usually several possibilities to repair or to exchange them. In all cases you must be careful to guarantee that all windows of a facade will look the same also in the future:

1. You may replace only the rotten parts of the windows by reproduction.
2. You will exchange such windows which are in poorest condition. The new windows must have the same form and dimension. The window has to follow the form of the wall opening, not the other way around (cheap standardized prefabricated windows).
3. As long as the facade is regarded not be of architectural quality, its windows have to match such a facade: if the majority of the windows are not repairable anymore, it is necessary to reproduce them as similar as possible to the original.
4. In cases where buildings are of a lower design quality, it may be possible to simplify windows: this would mean, for example, that windows with originally 6 glass fields could be substituted by windows with a T- division. In such cases the vertical and horizontal components of the window divisions are nearly the same in percentage.
5. But it is not possible to reduce the division further to a window with only one horizontal transom. This would give the whole facade a too intensive horizontal component; the character of the building would not fit with the windows. This kind of reduction was often used in the Western European countries, when people wished to use laminated glass panes. You should know and include in the argumentation for new windows that such laminated glass panes do not last forever. It is not a question whether but when they will turn blind - after 5 or 25 years? So they are a product for consumerism. They will produce costs again and again in more or less long time distance.
6. Never use pseudo-divisions! If they are within the laminated glass, you very often will not even notice them, as the light is reflecting them away. Then they have no visual effect any more. If they are outside of the glass panes, they are usually fixed with glue; after some time the glue will not stick any longer and the divisions will fall out and they have no longer an effect. On the other hand: form and construction should fit together - if you have a glass dividing window element, the you should see it, if there is none, you should not show pseudo-divisions. Real vertical divisions make the casements smaller and this is often very practical.
7. If you ever should use the materials plastic or metal, the profiles must have a form that can be copied in wood; very often profile-types of plastic or metal windows are changed. If one of the windows of a huge facade breaks, you may not get the same profile anymore after some years. This caused in many cases three or more different types of windows within one facade which creates a "slum image" for a building. The profiles must be designed in such a way that rainwater can run off and does not collect on horizontal details of the wooden copy of such a window - otherwise the windows made of wood will rot very soon.
8. If you wish a better insulation against cold, usually a double-window should be sufficient. If not, you should have the old windows at the outside and place modern windows with simplified divisions at the inside.
9. You always should pay attention to the fact that the old glasses are not perfectly plane. This causes an interesting glittering when there is a reflection. In most countries the offices for the protection of monuments and quite a lot of people collect such old panes of glass for this reason.
10. The dimension of profiles of wooden divisions (also of new windows for old buildings) have to be minimized, otherwise they will look very heavy compared with the rest of the facade. They would be in contrast to the character of such a facade.
11. To make old windows more efficient against nose you should exchange the glasses. Take glasses of different thickness for the inner and for the outer window pane to eliminate different wave-length of noise with the different glasses. Besides this, it is often necessary to mill so-called lip insulation into the profiles of the casements, and to adapt the old window by placing a better insulation between window and wall opening.
12. To reduce the escape of energy through old windows it is usually necessary to make the insulation of the inner windows more efficient. This can be done by the same lip insulation you have to mill into the casements - again: you must make sure that the outer windows are less well insulated than the inner ones. Otherwise you must expect condensed water at the inside of the outer panes of glass. Apart from this, exchange of air in the rooms must be ensured. We know that air with too much humidity needs much more energy to be heated. Every person gives off humidity - so it is necessary to bring drier air into the room through the window. It is a fault to hope to save energy by keeping the windows closed.

Industrial windows of plastic or metal often are a problem even in facades of new buildings. The design of such industrial windows changes quite often. Such a change creates - as already mentioned - many problems. Usually you do not get the same plastic-window for a longer period. But there are also problems with the metal work of such windows. It is possible to change the metal work of a window made of wood by milling the new fittings into the wood. The adaptation of such modern window is usually not possible. Windows made of plastic or metal are usually not repairable.

At a student hostel in my home-town Graz they had to reproduce the metal work of metal-windows by hand, as the company that had produced the fittings was shut down after the hostel had been built. The metal work for each window where the fitting was broken cost much more than the original windows all together. Cheap plastic and metal windows are not justifiable for another reason. In old buildings wall cracks caused by subsidence have to be expected along the window axis. if this happens with industrial plastic or metal windows, you will not be able to open or close them anymore.

But there is still another argument against industrial windows: Of course industry will need workers for the production. But each job there will cost several jobs for workers who could repair the old wooden windows. Unemployment will rise with industrial windows. Also to produce aluminum you need much energy and much of the raw material bauxite. Plastic is a problem for the environment. So I ask you not to change all the many individual wooden windows of historic centres for industrial standardized windows as this will create numerous problems.

Za povecavo kliknite na sliko
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fig. 1	fig. 2	fig. 3
fig. 4	fig. 4

Figures

Fig. 1
Inverness; the left half of the house has been modernized.

Fig. 2
Vienna; the new window design does no fit with the old - it is dominated by one horizontal transom, the old design by vertical dividing bars.

Fig. 3
Typical window of the 19th century.

Fig. 4
Typical surrounding of a window of the historistic period