Old wood windows and doors in poor condition can be restored and brought up to better performance.
The construction of these older units may be quite complex, with delicate joinery and moulding profiles. When dealing with this kind of assembly, ensure that you have someone skilled in restoration techniques who will treat the unit properly and with care.
12 over 12 wood windows with single panes and matching storm windows
Here are some important considerations:
Caulking may be used to fill gaps smaller than 1/4"
Foam backer rods and caulking may be used to fill larger gaps
Old doors are likely solid wood and may need to be tightened up at the joinery.
Install weather stripping around frame openings and functional parts.
Single glazed (one pane of glass) units may be replaced with thermal units, OR enhanced with the use of storm windows.
Weight pockets may exist on the vertical sides of the window frame. These voids should be treated with air sealing and insulation.