A typical Irish cottage has thick walls and tiny windows for a good reason - the best way to withstand winds in the past was to have thick walls rather than draughty windows. Glass technology has moved on to allow for glass with various properties such as low U-values (cutting down heat flow to the exterior), good thermal performance, known as low-E glass (standing for low emissivity), and good insulating capabilities (denoted by its R-value). While double glazing reduces heat loss, argon gas filled double glazing reduces it further as the gas conducts less heat than air. So now you can have larger panes of glass without undue heat loss. Tinted glass reduces heat gain.
It has long been recognised that people thrive better in spaces with large amounts of natural daylight. Look around at some new buildings or conversions and you'll see windows of different shapes, placed at haphazard distances from each other, windows not lining up vertically and tiny windows in large buildings. When considering adding windows to your home, think about proportion, symmetry and size.
Composition is key. Windows dictate the look of the building as much as the walls do. If you have a beautifully proportioned facade, it is best to leave this alone (you may have to anyway, if you're in a conservation area - check with your planning department). It is better to add windows to the side or rear.
Orientation is important. If you're aware of where the sun is, you will gain the most benefit from it in terms of heat and light. Windows on the south side get the most light whereas those to the north lose more heat. "South-east facing windows take advantage of early morning winter sun, warming the house or room after a cold night," says John Dorman, who designed a house in Connemara with carefully placed windows.
An example of design excellence is the Georgian window so it's better to repair rather than replace these. It's also worth considering their design benefits when choosing a new window. Georgian windows are often tall, allowing more light into the depth of the room. The window reveals on the outside are often rendered and painted white, which reflects light sideways into the room. The shutter boxes inside the window are often angled at 45 degrees, which allows more light in. They also modulate glare caused by the bright exterior meeting the darker interior. They have thin mullions whereas many modern windows, such as PVC varieties, have thick mullions which can cut down the amount of light by as much as 10 to 20 per cent. PVC windows are less eco-friendly than wooden ones and the choice of colours is limited.
Taking a cue from Georgian architecture (while avoiding pastiche), deep rooms can benefit from high windows to allow light to penetrate the room. An additional window opposite or next to it will increase the light as will a pale coloured ceiling which throws incoming light down into the room.
Internal windows also enable natural light to penetrate a building further. "Windows can be located to light specific task areas," says John Dorman, who did this in the Connemara house by sandwiching a full-length window between the worktop and the eye-level presses. Tall windows enable summer sun, at high altitude, to light most of the floor (a short window will create more shadows).
Windows opposite each other allow for cross ventilation. "Small openings can be used to show particular views such as a distant mountain or lake, a specimen shrub in the garden or patio, the path of the moon or an urban roofscape. A window at eye level when you're sitting at a desk or dining table might frame a specific view, and a corner window allows for a wider view," says John. Low-level windows can be used for kids' playrooms and bedrooms. An excellent way of increasing light, as well as a sense of space, is to install a large opening (such as French windows) out to the garden.
Roof lights can provide up to three times more daylight than windows. Roof lights on the front of a building can look ugly so if you have a double pitch it is better to position a roof light in the valley where it can't be seen from the front of the building. If you do have a roof light to the front, paint the surround the same colour as the rest of the roof to make it less obtrusive (glass is seen as black from the exterior).
Internal stairwells benefit from being lit from above - this can negate the need for a light here during the day. Because increased light is more beneficial in living areas than bedrooms, although radical, you may want to consider changing the layout of your home and having the living space upstairs. Velux is the well-known roof light brand; another is the Skytube, which is a clear dome that sits on the roof and takes light down into the house through a silver reflective tube designed to maximise light transmission. "If you are building an extension and thereby making an existing room an internal one, a roof light will allow natural light and ventilation back into that room," says John Dorman.
When placing windows, think about what the room is used for: living spaces benefit from good light throughout the day. Try to have less-used rooms (utility, storage, toilet) on the north-facing side. Studios or work rooms benefit from the steady even light provided by north-facing windows or diffused roof lights while bedrooms on the east side will benefit from the morning sun (and might help you wake up).
You must always consult a structural engineer or reputable builder when adding openings to walls as they are load-bearing. Adding roof lights will also have implications for the strength of the roof structure as you will be cutting rafters - adjacent rafters may need to be strengthened and perhaps bridged.
When deciding on extra expanses of glass you'll need to consider privacy. One-way or frosted glass may be used but they will cut down the level of light. The amount of privacy you require depends on your personality. Philip Johnson, designer of the Glass House in Connecticut, was asked about this and said: "Whether you want to close yourself in is Freudian in one way, but exposing yourself is Freudian in another way. Naturally you don't want people to be looking. But what about it? That little edge of danger in being caught ..."
