What is this on the roof?

[mnahmnah]

Hi

Calling anyone who knows about roofs!

We have just had an offer accepted on a house. But we can’t work out what this could be on the roof. Most of the houses on the road have some grey streaking like this. Another has it in the same place. Is it a concern? Thanks!

Need to see what’s above the marks ? Chimney? Tv aerial ?

Chimney - you can see on the full picture if you tap on it. Other houses have patches of it when not under the chimney though.

Aerial as well actually - you can just see the bottom of it

Better picture

water or some sort of weathering thats made some of the tiles cleaner than the others ?

or bird droppings thats ran down in the rain

Well most houses round there have patches like this somewhere on the roof and they all look like something has run down from the top. Rather than algae or loss growth.

Does bird poo stain? Or could it be metal from the chimney flashing or aerial?

If the hoises used to burn coal, maybe the soot generally blew in that direction and as it's acidic, reacted with the tiles to discolour them (or prevent dark-coloured moss/algae that is discoloring the rest?)

unlikely to be the metal, id guess either chemicals in the rain or bird droppings mixing with the rain water, i could be wrong but there my first guess, unless its excatly the same area on every roof nearby, then id consider the metal as a common factor

Thanks everyone. It seems it isn’t an obvious sign of something wrong!

I was expecting there to be something like a copper or brass metal object at the top of the roof, as the traces of metal in the runoff can prevent any moss/lichen growing and result in part of the roof or wall being a different colour over time. Not sure what's happened in this case, though.

It looks like your TV aerial overhangs that part of the roof. I would guess that acidic bird poo is falling on to the roof and gets washed down by rain. So either the bird poo is staining the tiles a lighter colour or it is keeping the tiles cleaner (i.e. what you are seeing is the original tile colour).

Pigeon crap.

Good old pigeon poo! Brilliant.