Windows have had different forms and functions throughout history: from holes in the wall to look (and shoot) through to stained glass to tell stories. However, in an energy-efficient home, windows have another function, and that influences, for example, the material and design you use. In this article I will tell you more about the value (and necessity) of good windows. 

The functions of a window

The functions of windows have changed quite a bit over time. For example, the first windows were only small openings in buildings without glass and mainly provided (day) light and air. When glass became available, windows also became a status symbol for the wealthy. In some countries there was even a window tax: the larger the window area, the more you could pay. Later, stained glass also emerged (as in churches), with which, for example, biblical stories could be told. 

Nowadays, windows no longer tell a story so much, but they often have to be aesthetically pleasing (after all, appearance does matter). Yet even today the window still has three traditionally important functions. First of all, it ensures that you can see outside (or inside), secondly, it lets light in and finally, it also keeps heat in. However, in energy-efficient homes, windows can also be an essential part of the heating system.

The weakest link

Ideally, you want windows to let in a lot of natural light, heat the house through sunlight (but not too much) and lose little heat (especially in winter). In many homes (even well insulated), however, windows are in practice a weak link in 'the outer shell': where exterior walls, the floor and the roof are increasingly better insulated, 20 to 40 percent of the heat in a home is still lost through the windows.

This can, for example, mean that windows are not a net energy producer on cold days, but energy consumers. The total energy gain from solar heat is then less than the amount of energy lost through the windows because they insulate moderately (compared to the rest of the home). That's a shame, because you don't have to heat up what doesn't go out as heat (one of the principles of the trias energetica). The strength of passive houses, for example, is that the windows are so good that they bring in more heat during the winter than escapes outward.

Also important is the principle of 'cold downdraught'. This occurs when warm air in the home comes into contact with a cold surface, such as a poorly insulated window. This causes the air to cool and 'fall' down. This creates an air flow (draught) that is very uncomfortable.

On the other hand, a home can also heat up too much on sunny days, especially if the sun shines on the glass. That is why you must be able to block solar heat with sun protection. You can use various techniques for this, such as an overhang, external blinds, coating on the glass, an adjacent building or even trees.

Characteristics of good windows

Windows therefore have a major influence on the amount of sunlight and heat that comes in (and goes out). That is why it is important to think carefully about a number of factors that influence this.

Glass

First of all, the glass. This includes the number of layers of glass and the thickness of the glass (such as double or triple glazing). Different coatings on the glass also have an influence, as do the gas fillings (or vacuum) that can be placed between the panes and thus form an extra layer of insulation.

Window frames and installation

But there are more factors that are important, such as the window frames. Its material influences the heat loss. You can choose wood, aluminum or plastic (be aware of the environmental aspects of the last one). The installation of the window in the wall opening can also form a thermal bridge, for example if the frame is not aligned with the insulation.

My advice is to use natural materials. Here you can read why.

Insulation and airtightness

A sustainable house is well insulated and built airtight. You won't feel a draft anywhere, because doors and windows also shut completely. Because you hardly lose any heat, the temperature is very even.

This does not mean that the windows cannot (or may not) be opened. Windows can also be opened in energy-efficient homes, but this often adds little value because the ventilation system provides sufficient fresh air without losing energy.

Location

Naturally, in addition to a high-quality window, its position in the house is also essential. Never orient large windows to the north, just like the rooms that you want to be warmer (such as the living room). And how about the size of the windows: more window surface provides more light, but - if you don't think about it carefully - can also lead to a home heating up more quickly and becoming too hot.

Windows in a sustainable house

Windows are also indispensable in sustainable homes (they even have a very important function), but all factors make it important to look carefully at the glass and frames. They must be carefully designed and selected. You must take into account, among other things, the climate, the orientation of the house, the amount of sunlight (and position of the sun during the year) and the materials used.

In short, windows are an integral part of an energy-efficient home and its design. Would you like advice about that? Please feel free to contact me.