We have triple paned tilt-turn windows from Germany. My comment is that if you split the window in two and both sides are operational, that window will be very heavy. It is not a problem for the tilt position, but if you swing it open, when you swing it closed you may need to lift it slightly in order for it to close properly. I am basing this on the windows we have that have openings about that size. I like WoW's idea of a 25:50:25 window.

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Sophie - I disagree. I did not design this. I have no pretensions to being a designer and for many other aspects of the renovation we have indeed had formal plans drawn up. [I also know from experience that having an architect involved is far from a panacea .... but that's another story or stories]. For this room we knew we needed to replace the large leaky picture window and instead of replacing in kind we asked whether it would be possible and reasonable to build a window seat and what would be involved. We showed the contractor many pictures of window seats and shared the required dimension ranges (not exact dimensions) from various articles. He said a bay window would take care of it and no separate plans were required. I include the manufacturer's literature excerpt that says their Bay and Bow windows can be used as window seats. It seemed (and actually still seems) a reasonable solution. Projection Window Bay and Bow windows are like a piece of fine furniture for the façade of your home. These unique windows project from your home, creating additional space that can be used for a variety of purposes, such as a window seat or displaying meaningful trinkets. Our vinyl windows (typically double-hung or casement windows) are inserted into a solid frame to create this unique look that adds style to any home. Bay windows typically have three lites (one central fixed lite and two flanking operational lites) at 20-25-degree angles. Bow windows most commonly consist of four lites, all of which can be fixed or operational, set at 10-15 degree angles. The contractor asked us to describe what we wanted to the window vendor as well and we did. We never used the term bay window. We only talked in terms of window seat. The window vendor also did not dissuade us or suggest we needed an addition instead of a window. The window vendor spec'd the window we needed. Given that we have 8 foot ceilings - this would have been a really good place to catch that a 52" bay window wouldn't be long enough to provide a seat at a reasonable height off the floor. I think that's the key flaw here - plus someone's telling us that (unless I'm wrong) we weren't going to get the wood backing. Tomorrow should be interesting ...

If you choose aluminum clad wood, be aware of the maintenance issues, particularly in certain climates. Years ago, the upper end of some brands of wood casements were made using Douglas Fir. When the casements were left open for long periods of time, the windows failed to close properly. Although I doubt that's an issue at present, it's something you may wish to inquire about. If you're seeking virtually no maintenance, go with fiberglass. It lacks the warmth of real wood, but avoids maintenance on wood sections. W hatever you select, you'll need skilled craftsmen to provide you with superior installation skills. You'll notice that some parts of the country have experienced many more installation problems than others, dependent upon the brand. Marvin appears to have a stellar reputation. I agree with millworkman's rankings. Loewen makes great doors, as well. Research the dealer's/installment team's reputations, as well as the company's customer service/warranty.