There are many purposes a window can serve and several of these have important ecological considerations:
- Letting light in
- Collecting solar heat
- Providing a view
- Acting as a door
- The visual character of a house
Windows may have associated drawbacks to consider:
- They may let in too much light at certain times
- Too much heat may enter
- They may be leaky in terms of draughts, rainwater and heat
- They may be insecure
- They may deteriorate over time
Using natural light whenever possible saves a considerable amount of energy. The amount of light entering a room through a window is partly to do with the window size but more importantly is to do with how much sky is visible from the window and the size and shape of the room. The light entering directly from the sky may be hundreds of times that which gets reflected from the ground or trees (although sometimes water can be used to reflect light up into windows).
The maximum amount of light is provided by roof lights positioned over the middle of a room. The layout of the house plan affects the amount of light entering, especially if the floor plan is narrow and deep. This was typical of Victorian terrace houses which tended to be dark in the middle, often around the stairs (on the other hand this was better for heat insulation as there was more party wall and less external wall and was also better for land utilisation).
A recent development is the light tube, or solar pipe, which is a metal pipe, highly polished on the inside which funnels light from above the roof down to the area you want it inside the house.
With heavily insulated walls there may be a strong argument for window reveals because the thicker the wall the more the light and view through the window gets cut off. Reveals are simply the shamfering of the corners around a window so that less light and view get cut off.
Take an extreme example of a passivhausSee more on the Passivhaus standard. The PassivHaus Institute has pioneered a standard for low energy buildings. It includes very low energy usage and ways of achieving this. The word is derived from the idea of buildings which are fundamentally low energy and passive solar heated rather than using extra gadgets to heat them. See Passivhaus for the UK branch of the organisation. wall incorporating a dry lining with service gap, 300mm of insulation and a 200mm stone outer cladding, with a 25 mm clearance between the two. In total the wall is almost 600mm thick. The plan drawing below shows a window which is 600mm wide.
With outer and inner splayed reveals (removing the corner of the walls at an angle of 45°), the area of room (the pink green and blue areas) which gets an outside view (and light from the outside) is almost double the amount compared with when there are no splayed reveals (pink area). The narrower the window and the thicker the wall, the more pronounced is the effect. The same goes for roof lights. The other advantage of splayed reveals is their ability to soften the contrast between the light coming through the window and the darkness of the window wall itself. This is not only pleasant but helps the eye see the wall more clearly.
A Pattern Language makes a strong case for thickened walls, particularly around windows, which create pleasant places to sit (179 – ALCOVES, 180 – A WINDOW PLACE , 197 – THICK WALLS , 202 – BUILT IN SEATS)
Collecting solar energy
Windows can be a major contributor in passive solar design. To do this there are four main requirements:
- There needs to be a large unshaded area of south facing glass
- There should be some way of capturing and storing the radiation – say a trombe wallA wall or part of one, acting as a solar collector. Often a layer of double glazing just in front of a heavy, black painted masonry wall, Sunlight heats the masonry. There may be openings (possibly controlled) which allow air to circulate between the glass and the masonry and thus heat the room behind. or dense dark floor
- There needs to be some way of distributing the heat to other parts of the house
- There should be a way of controlling the solar gain and limiting it when excessive
Most of the above are matters for experts to calculate. For more information, go to the Passive Solar Design section.
Views from windows
There are several reasons to consider what kind of views windows give. For instance:
- Seeing who is arriving. Many people feel more secure when they can see who is coming before the other people can see them
- Keeping an eye on small children
- Getting a view of the sky to see what the weather is doing
- General security and seeing who is around
- Views which are beautiful and inspiring – maybe parts of the garden or hills in the distance (on this subject there is a very interesting section in the book ‘Pattern Language’ called ‘A Zen view’ which makes the point that if there happens to be a very inspiring view, maybe a distant mountain, the temptation is to have a huge window in a main room which looks at it. In fact it can be more effective to have a small window in a circulation space[for the purposes of part B of the Approved Documents] A space (including a protected stairway) mainly used as a means of access between a room and an exit from the building or compartment such as on the stairs so that you just catch a glimpse of the beauty)
A window as a door
There can be great charm in being able to walk out onto a terrace or balcony through French windows, especially in summer.
The character of windows
The aesthetics of windows is quite a complex subject partly because of all the associations with different historic styles. Compare the traditional Georgian window with the kinds of Modernist design introduced into Britain during the 1960 and 70s. The Georgians were extremely skilled in joinery but the techniques of glass making could not produce large areas of flat glass. Hence the multi-paned, almost lattice like effect of their windows.
By the latter part of the 20th century, large sheets of float glass were readily available but the craft of joinery had been greatly deskilled. Coupled with this was desire for simple uncluttered shapes. Well, which era produced the better windows? Depends on your point of view. Certainly the Georgian windows have stood the test of time better judging by how many are still around but the obsession with sticking replica Georgian windows into contemporary design can look very peculiar!
In fact, finding good contemporary off-the-shelf window designs in Britain is very difficult, partly because many of the large manufacturers are still using old fashioned designs from the 1950s. This is probably why so many self builders either use Scandinavian windows or go to a local joiner.