Secondary double glazing can be used on the inside of the windows to stop drafts and prevent heat loss - much cheaper than uPVC double glazing and quicker to install.
External wooden windows and sills are subject to rot especially if South facing and exposed to the sun during the day. The paint cracks in the sun and water gets under the paint and rot slowly eats away the wood. So repair and maintenance of the outside is important for the long term.
Richard Buxton, October 2008
