Some interesting stuff there guys. Lots to consider, I have a roof am starting soon, and it's not so straight forward the top piece of glass has a lip on it about 10mm high, when quoting I was told that no water can go over the top of this lip, so I thought no probs, then reading this post am thinking maybe fan jets will be better as there won't be an over flow of water out the top of the brush.
Am thinking of putting 4 jets in all of my brushes