Doors and Windows - Creating double glazed window effect.

I have this idea that I could create the insulating effect of double glazed windows by putting a bead of silicon around the edge of existing single glazed panes and mounting a second pane of glass on top of the existing pane. This would create a seal and an air space and allow me to keep the old wood window. Do you think this (1) is worth the effort, (2) would have an insulating effect (3) would lead to moisture problems? Is silicon the right thing to use?

It's almost guaranteed to fog up -- other than that, it would work fine!

To do it right, you would have to order IG units from a local glass shop and glaze them in. However, it would cost about the same and be MUCH more efficient to simply replace the windows. And vinyls windows are virtually maintanence free. Assuming that your present windows are wood, they are any but maintenance free!

I've done to to tramsom (glass above a door) 14 years ago.....no condensation yet. I would say it almost as good as an insulating glass unit with a guarantee!!!! Maybe I was lucky....it may not always work.