Arched window treatments are not nearly as difficult to deal with as you may imagine. There are a number of options available, and you can usually adapt one or more of these to your own situation.
You can use these suggestion to enhance the attractive features of your window. If you want the glass or frame to remain visible, then use a system which doesn't hide them.
Or there may be parts of the window which you don't like. In this case use the fabric to conceal the offending areas.
How to visualize the effect
There are two things you can do to help you visualize the final effects.
Make a rough scale drawing of the window. Then cut out the effect you want using paper or card. Then place this over the original sketch.
So for example, in the illustration below (Curtains with pole) make a sketch of the window, and then cut out two pieces of paper of card to the shape of the curtains. You can also color these to test different colors.
Shapes to size
To get a more lifelike effect, pin up pieces of fabric or cardboard to simulate the curtains. This is particularly helpful to help judge proportions.
Straight pole or track
This is the simplest way to treat this type of window. The advantage of this method is that it works for all sorts of arches, whether they are tall or wide.
The track, or usually a pole, is placed high enough to leave a gap of about 4 inches (10 cms) minimum between the pole and the top of the arch. Also, don't forget to have the pole extend a reasonable distance either side of the window so the drapes can draw back enough.
You can arrange your arched window treatments to show or conceal as much of your window as you wish.
Ignore the arch
There are some arched window treatments where it isn't necessary to have the curtains cover the arch. It may be high up, or privacy isn't a concern.
So just hang the curtains from a pole or track placed at the base of the arch.
This can work in most situations, even if the window is wide rather than tall. Usually arched windows are quite attractive in themselves, and using this method shows the arch at it's best.
As the illustration shows, tying the drapes back to either side can add to the effect.
Curtains tied back
This method still uses a straight pole or track, but the curtains are left to meet at the top, and are tied back. It works best if the ties are placed towards the top, so keeping the curtains clear of most of the window.
Consider using this style if you have an arched window which isn't very attractive and you want to hide it. Or if you simply don't like the arch itself - it takes a skilled builder to install an arch which is pleasing to the eye.
Many attractive arches have a pleasing curve which can be quite subtle.
This needs more effort, because you'll need to get a pole or track bent to match the curve of the arch. There are companies who will undertake this, but you'll need to give them accurate measurements.
If you're unsure of what you're doing, you may be best getting a local home decorating business to do the work for you.
This method does have the attraction of keeping the curve of the arch visible. But you won't be able to draw the curtains back; they will have to stay fixed in position. Because of this, the headings used are often more elaborate than normal, and can give a more 'designer' look to the window.
Curved cornice box
Similar to the last method, this is usually easier to implement, because the track can be straight. This means that the curtains can be pulled open and closed as normal.
The shape of the cornice box needs to be chosen carefully for your arched window treatments. You don't want the narrow section in the middle to be too thin, nor do you want the outsides to be too long! A careful compromise is necessary.
You can find some general designs for curtains on the curtain designs page of this site.