All 4 of my bedroom windows have rotten exterior sills that badly need replaced. I have had 3 quotes from window restorers / joiners and the prices vary depending on method. Some say it is necessary to replace the whole sill, including the part that runs under the window frame to the interior wall, others say they only need to cut out the exterior part and then replace it with half of a new sill, cut to fit. Only thing that worries me though is how weather proof would the join be?
Any advice would be much appreciated.