Any ideas what’s caused this roof discolouration?

[CovBoy]

Hi,

I’ve just viewed a house a couple of times, put an offer in, had it accepted.

While daydreaming over the photos last night, i’ve just spotted something that i’ve not noticed before

There is a loft conversion with 2x Velux skylights. In a pic of the rear of the building there is significant discolouration under each of the skylights. I’ve asked the vendor what’s caused it via the agent and the response i’ve had back is “it’s due to water running down”.

I sent a short reply back saying that i’d not seen anything like that before and that i’d thought a roof was designed to get wet, so I’ll ask about for some additional advice (difficult to say without sounding sarcastic).

So... any ideas what could have caused this and if it’s anything to worry about?

Cheers

Ben

 

[footprints]

I expect it is quite the opposite! Less water flow over that bit so the c**p doesn't get washed away.

 

[JohnD]

it may be that the metal around the rooflight flashing is putting additives in the water that kill the moss and lichen growing on the roof, which make it look dirty. So the "stain" might actually be clean tiles. Or it could be some kind of sealant or other material leaching out.

Copper does that. I don't know if lead or other metals do.

"Acid rain" in industrial areas may cause more leaching.

There is a similar mark round the chimney, which looks like it has lead flashing.

 

[datarebal]

very early velux had untreated lead front aprons. it maybe that...

 

[catlad]

I changed an old velux yesterday with the old style lead apron, and that will leach down the roof poisoning the moss
and causing the discolouration.

 

[datarebal]

I changed an old velux yesterday with the old style lead apron, and that will leach down the roof poisoning the moss
and causing the discolouration.

I hope you are claiming your rewards!

 

[catlad]

Iv'e been leaving that to the mrs, she is going to
cash them in at christmas