I'd like a sliding door/patio at the back, but the width of the space it would go in is only 2700 mm. Can you get something that slides on/in an outside sunken track/rail? Like this...
Not seen anything like that before - doesn't mean it can't be done though. 2400mm is considered a large sliding patio door by standard sizes. Most are smaller.
If you're after maximum air, then you could look at 3 way sliders, or of course bifolds. Like Willie I've never heard of an outside window: I guess you could fix one thus and weather it in but I wonder what Fensa and/or BC might say and I suspect it would look pretty rough.
Thanks for your replies. In my head I had a single glass panel, but a 3 way sliding door or bifolds seem a decent option I suppose. Probably just end up with french doors once I've priced it up.