What's the opening part of a window called? ... can you buy them separately?

opening light(s) but I doubt you can buy one separately, double glazing firm that's ripping old ones out maybe?

Typically a casement window, so the swinging bit with the glass is the casement. However some people will call it the sash. (which if sliding rather than hinged, gives rise to the sliding sash window)

You could make a new one (or have it made), but commonly they would be bought as a whole including the frame since modern ones (even if made to look traditional) will usually have custom edge profiles to mate more closely with the frame giving better draught proofing etc.

The OP could buy a new version of the one he's got (i.e. the whole thing) and throw away the frame. That way he doesn't have to remove and re-insert the frame from the building, which I assume is what he wants to avoid.

Just a thought.

Another Dave

OP here. Yes, I could buy a whole window but that would cost several hundred pounds which seems a bit OTT when all I actually need to do is replace the bottom section/moulding of the opening piece.

I can see myself getting the router out and actually making a piece at this rate! :-)

sash

This is a DIY group. I just spent a few hours trying to mend a lawnmower. Eventually I just bought a new one. If at first you don't succeed, quit.

Good luck.

Another dave