Several times I have seen additions added to homes that maybe shouldn’t have been, or should have been built on a little differently. In our nothern Minnesota climate the weather really needs to be taken into account. Rain and snow are both big concerns. Hopefully there is a photo attached here of a garage roof added on too close to a window. I recommend as much room as possible, 8″ or more if possible between windows and new roof-lines being added to the home, or designed into the home in the first place. In this photo, you can see that the bottom of the window sill is deteriorating because of a large ammount of snow that sits on it now that there is a roof right below it.
Rain also is splashing on the window now far more than it would have been if there were more space between the window and the roof. There is also moss on this window sill, a sign that it is wet often. I would also like to see more space between the shingles and the siding, with a little bit of the step flashing exposed, to there is nothing blocking or holding rain water on the roof. I want it to drain quickly. The hardest thing I see on the average home is water. The dryer a house is, usually the healthier it is.