Mystery roof leak - updated - found the cause!

Apodemus

You appear to have an overflow pipe coming out of the soffit. 

I've had experience of a similar arrangement where the pipe had a slight upturn, where it crossed the top of the wall, before turning down outside.  This allowed water from a slightly dripping ball valve to pond in the pipe. Summer temperatures in the roof space meant that no external dripping was visible and I presume that the water was evaporating from the pipe.  However, in winter the water built up in the pipe and the pipe must have cracked during a freeze, leaving the overflow dripping, albeit very slowly, onto the ceiling where it became visible in the room below.

Tucosalamanca

I think it needs to be stripped and re-laid, new felt and batten at the minimum.
I can see lots of potential defects but also lots of previous repairs (some which appear to be rather old).
Once it gets to that point, it's a constant battle to stay on top of.

For the immediate problem - this is where I'd be looking.
Vent to right of above dormer window - potential entry point.
Tiles around this vent have been previously disturbed.
Evidence of previous works above your problem area - different tiles etc - this would be my first point of call
Ridge tiles above appear to have been previously re-bedded.

Other issues.
Bottom of dormer frame and window appear to be beginning to go rotten, this should be addressed before it gets worse.
There is an eave tile missing under the dormer window.
The apron flashing looks short (in fact all flashing look less than generous, I'm sure there are reasons why)
Stonework under the dormer and guttering appears to have water marks. I'd take this as a strong clue to more problems in this area.

dharm999

Tucosalamanca said:

I think it needs to be stripped and re-laid, new felt and batten at the minimum.
I can see lots of potential defects but also lots of previous repairs (some which appear to be rather old).
Once it gets to that point, it's a constant battle to stay on top of.

For the immediate problem - this is where I'd be looking.
Vent to right of above dormer window - potential entry point.
Tiles around this vent have been previously disturbed.
Evidence of previous works above your problem area - different tiles etc - this would be my first point of call
Ridge tiles above appear to have been previously re-bedded.

Other issues.
Bottom of dormer frame and window appear to be beginning to go rotten, this should be addressed before it gets worse.
There is an eave tile missing under the dormer window.
The apron flashing looks short (in fact all flashing look less than generous, I'm sure there are reasons why)
Stonework under the dormer and guttering appears to have water marks. I'd take this as a strong clue to more problems in this area.

Thanks for the detailed answer.

The area with the replaced tiles is above where the leaks are, would the vent, which is quite a long way from the area of the leak be a likely cause?  Or can water travel that far?

Same question re the ridge tiles

There is no sign internally of any leaks under the dormer, where there are water marks, so not a problem, but it sounds like it could be just a matter of time before it is.

The last roofer who came, said it would be around £120-£130/sq m to replace the slate tiles with an equivalent tile, less if we went for Spanish slate, as they are more uniform and easier to lay.  If I replace the tiles in from the gutter upwards to the ridge and to the left of the dormer, it looks like 40-50square metres, so around £5000-£6000 as it would look odd to go for a different tile for half the roof to what is on the rest.

Sounds like I may have to bite the bullet and get it done.

The window in the dormer is going to have the sashes replaced with double glazed ones and the dormer painted, early in the new year, so hopefully that will sort that problem.

dharm999

Apodemus said:

You appear to have an overflow pipe coming out of the soffit. 

I've had experience of a similar arrangement where the pipe had a slight upturn, where it crossed the top of the wall, before turning down outside.  This allowed water from a slightly dripping ball valve to pond in the pipe. Summer temperatures in the roof space meant that no external dripping was visible and I presume that the water was evaporating from the pipe.  However, in winter the water built up in the pipe and the pipe must have cracked during a freeze, leaving the overflow dripping, albeit very slowly, onto the ceiling where it became visible in the room below.

Thanks for the reply.  The leak is around 4 feet in from the wall and also from the top of the window frame on to the sill.  The overflow pipe might explain the leak from the window frame, but I think it’s unlikely as the pipe runs from an upstairs toilet but I will investigate.  Am happy to try anything as it’s getting frustrating not getting it fixed, as it’s stopping a refurbishment of the downstairs bathroom with the leak.

plumb1_2

I’d check around the vent with the cowl, no weathering collar on the pipe, plus slates look iffy 

Tucosalamanca

dharm999 said:

Tucosalamanca said:

I think it needs to be stripped and re-laid, new felt and batten at the minimum.
I can see lots of potential defects but also lots of previous repairs (some which appear to be rather old).
Once it gets to that point, it's a constant battle to stay on top of.

For the immediate problem - this is where I'd be looking.
Vent to right of above dormer window - potential entry point.
Tiles around this vent have been previously disturbed.
Evidence of previous works above your problem area - different tiles etc - this would be my first point of call
Ridge tiles above appear to have been previously re-bedded.

Other issues.
Bottom of dormer frame and window appear to be beginning to go rotten, this should be addressed before it gets worse.
There is an eave tile missing under the dormer window.
The apron flashing looks short (in fact all flashing look less than generous, I'm sure there are reasons why)
Stonework under the dormer and guttering appears to have water marks. I'd take this as a strong clue to more problems in this area.

Thanks for the detailed answer.

The area with the replaced tiles is above where the leaks are, would the vent, which is quite a long way from the area of the leak be a likely cause?  Or can water travel that far?

Same question re the ridge tiles

There is no sign internally of any leaks under the dormer, where there are water marks, so not a problem, but it sounds like it could be just a matter of time before it is.

The last roofer who came, said it would be around £120-£130/sq m to replace the slate tiles with an equivalent tile, less if we went for Spanish slate, as they are more uniform and easier to lay.  If I replace the tiles in from the gutter upwards to the ridge and to the left of the dormer, it looks like 40-50square metres, so around £5000-£6000 as it would look odd to go for a different tile for half the roof to what is on the rest.

Sounds like I may have to bite the bullet and get it done.

The window in the dormer is going to have the sashes replaced with double glazed ones and the dormer painted, early in the new year, so hopefully that will sort that problem.

If the membrane is working well, yes water will travel (vent and ridge).
It's possible that the timber battens have been absorbing water in the summer, once heavier rain starts, the timber becomes sodden and water tracks down until it finds its level.

I would say that's a very fair price. I generally use first quality Spanish slates (think they're really good value) and would be charging closer to £150psm (south uk).

The dormer roof looks like a very tidy lead installation, so it makes sense to keep on top of the rest.
Good luck with it.

dharm999

Had a Homer Simpson ‘doh’ moment.  I had completely forgotten about an access door into the eaves, right where the leak is.  I’ve attached a few pictures that show a very damp roof support and water pooling at the bottom of the truss, directly above the leak.  It looks as if the leak is quite low down in the roof, so not due to the vent, but I’m not sure, and happy to be proven wrong if that isn’t the case.  Next time it rains I’ll check the access door and see exactly where the water is getting in.  The third picture shows a wider angle and the roof truss has signs of water on the vertical, but isn’t actually wet at the moment.  The part lower down is very wet and I assume water is dripping from that down, to where it is pooling in the first picture.  Do folks think that my guess that the leak is low down right?

Why there is rubble in the loft, I don’t know, but I will get rid of that, it was hidden under the insulation.

dharm999

Anyone agree, or not, with what I think?

Bendy_House

No idea. But sarking boards (presumably) covered in felt can transfer the water right down to the eaves from wherever it originates, even from a ridge tile. So it isn't evidence of a low-down leak. The water will just come through where it can.

Apodemus

With sarking boards on an old house, there might not be a felt layer at all.  It looks as if there is a damp line at each sarking board joint in pic3?  All that you can say from that is that the water is coming from higher up the roof than the highest of the damp lines, possibly all the way up to the ridge.

I once lived in a house with an exposed ceiling, where the sarking boards formed the interior face of the ceiling.  During wet weather, after a long dry spell, you could lie in bed at night hearing the drips getting closer as each sarking joint in turn leaked, then sealed itself as the wood expanded and the water moved on to the next sarking junction lower down.  Problem there was fixed by relaying the ridge tiles.