Possible corroded lead tapered gutter

[Daniel P]

Good evening all.
This the first time of posting and I hope to find a solution to this problem.
I have a butterfly London roof with parapets all around. The gutter is lined with code 6 lead, which has 4 steps and 3 rolls, on geotextile on 18mm WBP ply. The roof is covered in eternit slates over tyvek breather membrane.
I was considering yesterday, the issues of venting the roof as I had planned to install loft insulation.
Yesterday, while inspecting one of the lead bays, I noticed a white powder under the bay and the bay timber was bone dry. The gutter doesn't leak, yet. One bay had a redish/blackish markings
My heart sank.
1. Could this be corrosion of the lead due to condensation or something else?

2. I've read that ventilation is the key. As the ceilings are in place, I can't install a vapour barrier or?

3. Where would the vents go? I envisage some form of low level vents by the gutter and high level on the roofing slatest.

4. Is is possible to rescue the lead, or is it a question of total replacement and carrying out remedial work that caused it?

Your advice will be much appreciated.

 

[datarebal]

Have you pictures ?

 

[Daniel P]

Thank you datarebel,
I've enclosed photographs.
Two of the general gutter and 2 of each bay in the 2nd and 3rd position. I have not lifted the first bay at the hopper end of last one at the front elevation.
Many thanks

 

[datarebal]

First thing I see is repairs. It's not code 6
Third bay back are about 2.1 in length.
The lead may have been laid on a damp/ substrate.

Looks shoddy to me

 

[Daniel P]

Thank you datarebel
It's code 6 unless the roofing merchant is selling code 5 as code 6. It has the black tape on on the reverse of it. I could check the gauge on an area that would not have had the lead beaten and come back to you.
If I remember correctly, those many moons ago, the substrate seemed dry at the time, but i couldn't guarantee it wasnt damp when the lead person laid it.
Oh yes, it's shoddy!

So what is the white, black reddish stuff and has the lead corroded?

 

[Daniel P]

Or maybe the repair was done in code 5?

 

[datarebal]

It certainly doesn't look Code 6. We use 5 ,6,and 7 on an almost daily basis. Obviously I am guessing from certain details in the pictures.
Not all deposits are harmful to the lead some actually protect it.

Venting the roof both sides top and bottom and of course make sure you insulate to a decent level

Why did you feel the need to fold back the lead bays?
That aside, Flash band repairs on the roll ends. it just carp.

 

[Daniel P]

My hands are up! The flashband was me.
That's temporary repair until I get it repaired properly. It split due to next doors scaffolders stepping on it and splitting it.

I took it up because I was looking at the damage caused and noticed the height wasn't 55mm at the first step. So I exposed it and saw the white stuff. So I lifted the other bay.

 

[catlad]

Looks like its slowly corroding to me, Probably from lack of ventilation, that said it could take years before it fails.

 

[Daniel P]

Thank you catlad and datarebel.
I'd have to relook at the ventilation aspect of the whole roof, especially the detailing around the gutter and do it asap.
The roof has no vents, but uses Tyvek breather membrane. The insulation is 100mm, which I was going to add to.

Seems like the scaffolders have done me a favour.....