We can often repair window sill rot with wood-epoxy, or by replacing the nosing. With this triple sill, the rot had gone so deep that it was beyond repair and had to be replaced. Almost half the job is removing the rotted sill without damaging any other parts of the window. Though we don’t show it here, we seal the end grain of the window components that come in contact with the new sill, and the new sill is prime painted before it is installed.
Click on the first image for detailed explanation of the process.