Anyone know how to stop water run-off from a full width dormer roof onto neighbours roof?

[MGMidget]

A question for anyone who has, is planning or knows a thing or two about full-width box dormer loft conversions. If the side cheeks of the dormer rise above the parapet wall (or there isnt a parapet) adjoining a neighbouring property, how do you stiop the water flowing off the flat roof, down the side of the dormer and onto the neighbour’s property? Is there a standard detail for this?

Ours was slightly sloped with a gutter

It surely needs guttering around the edges and a down pipe to take the roof water to the appropriate run off

Is there guttering that's inadequate?

We have a small dormer, (in the bedroom, small pokey cottage sort of thing for a visual idea!) with a pitched roof and that has a gutter round the edges that runs into a valley on our own roof, then into the gutters and down pipes, also have a flat roof bathroom that does similar. Although that goes across us and next door, his bathroom and ours....but I assume the rain is organised and his goes down his gutters and mine stays on my side! :o :o
I am going to have a proper look when i go out actually, I presume we have our own down pipes!

Thanks! In this case the flat roof of the dormer overhangs part of the parapet to the side. So the gutter (if one was installed) would have to be over the boundary. Gutters are at front of roof and at base of rear wall of dormer. Nothing at the sides. I was hoping someone would have something similar with a drainage solution!

If the dormer were to be re-felted (assuming its not lead) then a piece of arris rail placed at each side (under the felt) will guide the rainwater to the front edge. A bit like this picture

Ask the neighbour which they'd prefer! Your guttering on their side or the water! I'd definitely prefer guttering.

Oh my goodness, you're right - I went outside to check our own dormer and noticed in the process that the three other dormers I could see (and our own) all had this. I never knew!

Thanks everyone. Janek, do you mean that your dormer and the other dormers have an arris rail like shown in TwoLeftSocks' picture?

That's pretty simple to do I would have thought.

Are these arris rails higher than the rest of the roof including the roof ridge? I am just wondering because of the permitted development rules and the requirement not to build higher than the roof ridge and whether an exception is made for arris rails!

Yes, that is what I mean. And I've just checked - the roof ridge is very slightly higher than the arris rails. Our loft conversion was done under permitted development (although we got that certificate from the council to say it would be fine, on the recommendation of our builder).