Keep frames but replace single glass with double glazing?

[MrCheese]

The frames in my house are 1960's hardwood and in very good condition. Some are double glazed but most are single. They are nearly all non-standard sizes.

It seems a shame to replace perfectly good frames with uPVC so is it possible to keep existing window frames but replace the glass with double glazing? I assume double glazing would be substantially thicker and require the frames to be cut out in some way.

If it is possible, is it likely to make economic sense as I guess it would take a lot of time and skill to replace the glass.

 

[God]

You could use a step unit, this is the outer pane of glass sits where it dies at the moment and the inner pane is smaller and sits inside the frame, the unit will be 14mm thick, whether that will make much thermal difference I don't know

 

[ladylola]

I had the same decision to make on the windows when I moved in my present house. I didn't really want to (or could really afford to ) change timber for pvc so I deepened the rebates and ordered double glazed units with a 14 or 16mm spacer bar and fitted them.