Down pipe onto flat roof

[Bazza]

I live in a semi with a single story extension at the rear on the boundary line, last re-roofed in '92 but in good condition, standard type with chippings. The rainwater downpipe for both properties is on my neighbours side front and rear. When they moved in 2 years ago they replaced their guttering, I had mine done at the same time by the same contractor. What they did not do is connect the rear downpipe as when they had a new patio laid prior to the guttering, the drain disappeared somewhere underneath it. For the last 2 years the rainwater has been running down their wall and has blown the rendering, rather than let it spread to my side I suggested that they run the downpipe along the side of my extension and into it's guttering, I left a section jutting out onto their side when I replaced it this summer so they could do this. Now what they did last weekend whilst I was away is to run the downpipe directly onto my flat roof.

Will this be detrimental to my flat roof? If no damage will occur I will let it go rather than risk the damp reaching the rendering on my side, if on the other hand it may damage my roof having the water concentrated in one area I will ask them to move it. They have their house up for sale so I think they went for a quick fix and I would rather have it sorted now than have to take it up with the new owners.

Bazza

[Cod Roe]

I would insist on it being moved having just had to re-timber my back roof as well as re-permeable membrane and slate it due to among other reasons the down pipe from the main roof pouring over the roof in question at the point at which it abuts to a wall and only had a mortar flashing (with no soakers) for protection. The rot was spectacular, and when I took the timber out and left it in the open before disposing of it the first rain caused it to become covered in white spores within a few hours, I've never seen anything quite like it. The other side of the roof without the down pipe was in pretty good condition in comparison. The volume of the water, its speed, and the fact it is delivered in a "far more omni-directional sense" is murder, even for the best roofing jobs. I know slate isn't the same as flat roofing, but it isn't worth the risk, even DIYing it has cost me a fortune to remedy.

[The Natural Philosopher]

100% agreement with the above from here.

[dg]

The extra and concentrated flow of water from the downpipe, is likely to cause more wear and premature aging of the felt.

Now is the time to get them to do it properly, if not register a dispute, which will delay their sale until the issue is sorted. Don't wait until the new owners are in, as you don't really want to start on a bad footing, and they may well not offer to remedy it.

Or just go an sort it out yourself, if that is easier

dg