Our mildew stained and part rotten Velux window frames. Well they've been in over 20 years and get the worst of the weather so I can't complain. It seems condensation was the main issue which caused quite a lot of black staining and small sections of one of the frames to rot away. Thankfully wood preserver treatment followed by careful filling using a 2 part pine coloured polyester based filler and sanding has done the trick. It's been a bit of a job but satisfying as working with wood usually is. Just another 2 large roof windows to go and I'm all done for a few years hopefully...
