First of all - types of windows. What are the options for homeowners?
If it's a new house, it must have fire opening hinged windows to meet fire safety regulation. These are the windows which open at the side and they must be able to open the full 90 degrees. The law is looser for existing houses, but at the end of the day, safety should still be the top priority.
There are a couple of places where it's OK to use a different type of hinge. For example, a top hung window is allowed in a in a bathroom , because it's assumed that you don't sleep in a bathroom! Likewise, the downstairs windows in an existing house don't have to be fire hinged because it's assumed that you can exit through the doors.
Another exception are sash windows on a period house. The problem with sash windows is that the actual opening is small and often the only way out is head first. An elderly person or a heavily pregnant women may not be able to escape.
Tilt-turn windows are another option consider. They're fine as emergency exits but the fact that they tilt in or turn in can be a problem when it comes to window dressing. You may have to put a blind or curtain on the window itself as well as one the surrounding wall.
What about the choice of material for the frames?
At one time aluminium was a popular choice but it had failings. Aluminium a metal so it attracts the cold and introduces a lot of condensation. PVC has taken over from aluminium because it's doesn't have those problems and is still zero maintenance. Hardwood is also a very good material but it's very expensive. For example, if a PVC window costs 700 euro to supply and fit, the same hardwood window could cost 1800 euro. In addition, there's more damage done to the house during installation because the hardwood frame is wider than the PVC frame. An environmentally friendly option is pressure impregnated softwood frames.
What type of glass is recommended?
The type of glass used is absolutely critical for energy efficiency. The buzz word now (and rightly so) is K-Glass. K-Glass came in as part of the Kyoto agreement to cut down on global warming and has had a dramatic effect on energy efficiency.
By law, all suppliers have to sell K-glass. But homeowners should beware because a lot of companies make themselves more competitive by pushing the non K-glass option. They get away with it, because the homeowner was used to single glazing and a very cold house so their new double glazed windows seem to make a good difference. Unfortunately, if they had a good quality K-glass, the difference would be fantastic.
Another way to make your windows more efficient is to use an insulating gas like Argon between the panes of your double glazed windows. These gases are bad conductors which means that the air inside the room stays hot and the air outside stays cold.
Finally, what's the most important points to remember if you're buying new windows?
Safety first - will you be able to exit through the window opening?
Secondly, be kind to your energy bill and the environment and make sure you're getting K-glass. Get the best possible rating of K-glass. It comes in different ratings, with 1.1 being the most efficient.