Mystery leak in Roof between Velux Windows

[Gary Daines]

Hello

first time poster here hoping someone might be able to help me

had a loft conversion done two years ago and a leak has recently started to be noticeable inside in between the Velux windows after it rains

I’ve had a little look and to my untrained eye I can’t see anything obviously wrong

When it was dry the other day I climbed up onto the roof and poured water around the left window and it didn’t leak, but when it rained last night, it leaked again

my next job is to wait for the leak patch to dry and pour water around the right window but wondered if anyone may have any tips or pointers or if anything in the following pictures give any clues

thanks very much!

 

[datarebal]

try running water on the flat roof. it looks in a poor state.

update- post a close up of the top corner of the velux flashing where the back gutter turns down the corner..looks like it may have been modified

 

[Gary Daines]

Thank you

I can’t see any obvious problem on the flat roof. It was done at the same time as the conversion and had vents added with extra felt and bitumen at the same time. I’ve added a picture from a different angle


I’m not entirely sure where you mean with the top corner of the Velux but have added a picture of what I think you might mean

When I first noticed the leak a couple of months ago, I thought possibly a piece of tile was missing so I added a piece with some sealant incase that was problem (I’ve added a before and after shot)

but like I said, I poured water the other day from a bucket in that area and it didn’t leak after. Only when it rained yesterday

 

[mattylad]

Where in the velux is it coming through?

 

[ted456]

If necessary what about a hose sprinkling out from the Velux opener?
What are the three vent terminals venting?

But could be you've identified the cause of the leak at your repair job - that area needs stripping and re-doing dont use slivers of slate and always use fixings. You can cut and hole full slates to suit and some mfr's supply wider slates if needed. You shouldn't need silicone.
You can work from inside the Velux.

The back gutter to the chimney stack has been done wrong so has all the stack and parapet flashing.
Soakers under slate is best not on top of it
There's also a kind of sand and cement covering above the flashing, no need for that unless the roofers haven't used an angle grinder to chase in the lead cover flashing?
But if nothing is leaking then good but at least you know.

 

[Gary Daines]

Where in the velux is it coming through?

I can’t see it coming through the Velux specifically, but the damp patch that I can see inside is in the area of the roof between them, but closer to the left velux

 

[Gary Daines]

If necessary what about a hose sprinkling out from the Velux opener?
What are the three vent terminals venting?

But could be you've identified the cause of the leak at your repair job - that area needs stripping and re-doing dont use slivers of slate and always use fixings. You can cut and hole full slates to suit and some mfr's supply wider slates if needed. You shouldn't need silicone.
You can work from inside the Velux.

The back gutter to the chimney stack has been done wrong so has all the stack and parapet flashing.
Soakers under slate is best not on top of it
There's also a kind of sand and cement covering above the flashing, no need for that unless the roofers haven't used an angle grinder to chase in the lead cover flashing?
But if nothing is leaking then good but at least you know.

Do you mean spray water in that area from standing inside the open window?

Can try that but did pour water on that area the other day and no leak, only when it rained

the vents were a requirement from building control to increase the ventilation above the steel beam in the roof at that area

when you say can work from inside the velux, you mean you think I can strip and redo that area from standing inside the window? (As opposed to having to get scaffolding etc)?


Yes, I think they did not chase in the Lead flashing. No leaks from that, and it passed building control?


Sorry for the questions, this really isn’t my area at all

 

[ted456]

Yes, spray any part of either roof from the safety of inside the Velux, you can work on the repair from inside to..

Well ive suggested what i'd do?

Its not BCO's job.

 

[Gary Daines]

Yes, spray any part of either roof from the safety of inside the Velux, you can work on the repair from inside to..

Well ive suggested what i'd do?

Its not BCO's job.

ok thank you

yes, and what you suggest does make sense. I suppose i was thinking (hoping?) if building control noticed an obvious issue they might raise it

I suppose because I’m already feeling anxious about the current leak I almost don’t want to think there could be other issues, and because the flashing you mention doesn’t seem to have caused a problem, I almost don’t want to think about anything on top

so do you think the problem will be where I did the patch job?

that was my first thought, but considering it didn’t leak after I poured a bucket of water on it, but it did leak after it rained (Not that heavy) last night, I started to wonder if maybe the issue is located elsewhere

 

[Gary Daines]

I was also wondering if there is an indication of where it may be starting in the development of the wet patch

initially there was only a patch in the middle but this has got larger

I know water can move about in ‘mysterious ways’ but I wondered if it would be a useful assumption to consider the water is starting in the ‘middle’ then running to the left, collecting in an area and then working it’s way down

I’ve attached some pictures to illustrated my wonderings

 

[datarebal]

Strictly speaking there should be no small cut slates . That is why they make doubles.
the missing cut that you stuck in would not have leaked as the soaker is there doing its job.
i still think flat roof new or not its shoddy. Felt faults are rarely obvious to the untrained
I would be suspicious of the felt to lead bond...or likely lack of

 

[Gary Daines]

Strictly speaking there should be no small cut slates . That is why they make doubles.
the missing cut that you stuck in would not have leaked as the soaker is there doing its job.
i still think flat roof new or not its shoddy. Felt faults are rarely obvious to the untrained

hiya

thanks for that

if that was the case, wouldn’t I see evidence of the leak higher up on the plaster board inside?

i can only see it at the middle area

i found this old picture of the roof earlier in its construction and wondered if the water is running along this noggin here

 

[datarebal]

you can see it in the middle spreading side ways.
i still say flat roof

 

[Gary Daines]

you can see it in the middle spreading side ways.
i still say flat roof

thank you

Is there any particular area of the flat roof you think could be the issue?

 

[Gary Daines]

Strictly speaking there should be no small cut slates . That is why they make doubles.
the missing cut that you stuck in would not have leaked as the soaker is there doing its job.
i still think flat roof new or not its shoddy. Felt faults are rarely obvious to the untrained
I would be suspicious of the felt to lead bond...or likely lack of

Ive just noticed this bit about what you think could be the potential lack of bond between the felt and lead at the top

would there be any reason against me attaching some new flashband over the join between the existing felt and lead at the top of the roof where you have highlighted? If the problem lies there I wonder if that could be a solution?