There were two design issues with this porch resulting in considerable rot . The roof did not overhang sufficiently to allow water to run off into a gutter instead the water simply poured off the roof and onto the cills.
The leaded windows were not rebated into the frames they were simply placed onto and not into the frames . This resulted in rot developing around the glazed areas. I have never seen such a odd set up before. It transpires that the porch -circa 1930s was built to accommodate the leaded windows that came from a nearby manor house that had undergone some alterations.
The owner at the time was no carpenter and although a valiant attempt was made the timber dimensions were all wrong and for 90 years and several owners remained that way. This could have been demolished and a like for like replacement made. It would have been easier to do that but the owner wanted to keep the original. Air dried European Oak was used . Being air dried it remains more stable than kiln dried and will not split so readily as green oak.
The leaded windows once removed had the lead cames re-cemented this made them watertight and stiffened so that when replacing the risk of breaking the lead came was reduced. Replacement tie rods in bronze complimented the lead. Tie rods are used to prevent sagging over the long term and reduce the stress put onto them by high winds.
Once rebates were machined the leaded windows could be installed using traditional putty.
Wooden Window Repair 