Leak from channel or render?

[GillObrien]

Hi all,

We have a small damp patch in the corner or the room, which is never wet, but the paint flakes. For info, the wall is an outside wall, the building is concrete, the wall has some sort of plasterboard/insulation on the inside and the ceilings have a gap of about 20cm to the concrete floor slab above.

We have a large channel on the roof that collects rainwater from the roof, and a down pipe. The channel is the overhang you can see outside the window. It ends about level with the front wall, which is where the tiles start. I attach photos. It is old but doesn't leak anywhere else, plus the damp is offset from the channel. I looked in the eaves, which are difficult to access (the loft is converted) and it looks like there is a slight damp patch on the concrete loor above around this point. I don't see a drip.

The wall is rendered and there is a crack at around this level. However I don't know how superficial it is as it is high up. The repair you can see was done at the time because apparently the render bubbled at this point (it is the join between the concrete panels).

I asked a roofer/render to come and look at it, and he said, without looking really, that the leak is from the channel. When pressed him as to where, he was just vague and said it was old.

So, does anyone have any idea as to whether it is likely to be coming from the channel, the roof or the wall? We will get the channel and parapet top redone in zinc but I will also get the render done at the same time if needed. I will also ask another roofer, but I would like to understand first.

Many thanks,
Gill

 

[martygturner]

Looks like it is coming from the plant that as taken root in the corner.

 

[GillObrien]

I suppose. It grew this Spring and the damp has been there for two years and it is about a metre from the damp patch. I think if I went on the roof I could just sweep it off (too wet and windy lately). Debris accumulates in the corner and things grow in it.

 

[martygturner]

Its right at the point where the water is coming through on the outside...roots love to burrow....

 

[GillObrien]

So for the minute should I clean it all up and then somehow reseal that end of the channel?

And the render on the end wall, should I get it redone?

Many thanks!

 

[datarebal]

plenty of historic repairs have already been done. render and gutter need attention

 

[Sonic70]

Could it be due to the tile edge having no lead flashing but what looks like a fillet of mortar painted white?

 

[tell80]

OP,
It might help you if you checked out "How to repair a flat roof." by skill build on you tube?
It might give you ideas for temporary repairs, & what kinds of materials are available?
But first you would have to remove all loose materials, and have clean surfaces before any remedial work.

The bottom edge of the gable parapet zinc capping doesn't meet the channel parapet zinc capping - there's a gap that might allow water to enter the building?

The render on the outside of the gable wall requires hacking off back to "concrete" and re-doing.
Likewise the render on the inside of the gable parapet.

If the tiles are simply covered with a sand & cement fillet (as above) at the gable parapet abutment then that too could be a weak point.


FWIW: the chimney stack is in need of re-rendering & further attention. No sheet lead appears to have been used on this roof?
There's no grill over the channel outlet - some kind of gutter outlet guard or balloon would help to keep debris out of the down pipe.
Is the house in the UK?

 

[GillObrien]

OP,
It might help you if you checked out "How to repair a flat roof." by skill build on you tube?
It might give you ideas for temporary repairs, & what kinds of materials are available?
But first you would have to remove all loose materials, and have clean surfaces before any remedial work.

The bottom edge of the gable parapet zinc capping doesn't meet the channel parapet zinc capping - there's a gap that might allow water to enter the building?

The render on the outside of the gable wall requires hacking off back to "concrete" and re-doing.
Likewise the render on the inside of the gable parapet.

If the tiles are simply covered with a sand & cement fillet (as above) at the gable parapet abutment then that too could be a weak point.


FWIW: the chimney stack is in need of re-rendering & further attention. No sheet lead appears to have been used on this roof?
There's no grill over the channel outlet - some kind of gutter outlet guard or balloon would help to keep debris out of the down pipe.
Is the house in the UK?

I just saw this reply. The house is in France.

There are gaps all along the zinc which I am sure is the source of slight damp above a different window and some other render that has blown. The zinc expands and contracts and the joins never stay together. We are going to get it redone. The roofer told me the render was "only for decoration" hence I decided not to use him.

You can't see it clearly but the tiles are covered with a zinc "box" which comes out of the wall at 90 degrees turns down 90 degrees towards the roof and is cut to shape around each tile. It covers approximately 10cm to 15cm of the edge. Above this is the cement that you see, which slopes slightly and directs rain onto the zinc and then the roof.

There is no lead anywhere - this is the original construction. The channel would originally have been zinc as well.

Thank you for the advice. I remain convinced the damp is from the render, as in both areas where it is blown the paint peels inside. I am also sure that the zinc on the parapet allows water to enter the top of the parapet wall as you suggest. I will take a look at info for repairing a flat roof and put a drain guard.

Thank you for the heads up on the chimney. We are on top of a hill facing an open valley, so we get all the weather at full blast, plus fog etc, so the outside of the house takes a bashing!

Many thanks for taking the time!
Gill

 

[GillObrien]

To follow up. The roofer came yesterday and took a look. He thinks it is coming from the fact that the channel, which is effectively the concrete floor slab that extends outside the building, has probably a small leak somewhere along the old repair, and the water is penetrating the slab and soaking the ceiling. Plus there is no fall on the channel so water tends to sit in there.

He is going to replace the channel in zinc, as it would have been originally, creating a fall towards the drain. He said there is enough depth up to the tiles to do this and avoid any overflowing. He will also replace the zinc on the parapet, first putting a wood plinth so that the zinc is not screwed directly to the concrete as now and avoiding any exposed screw holes.

He also proposed to do the sides of the roof, running the zinc under the tiles rather than on top (because apparently the last tiles before the walls are cut before the hump in the profile, so are flat, hence water can.tun off the edge under the zinc and down the wall.

So thank you all, it really helped me to ask the right questions @tell80 @Sonic70 @datarebal @martygturner

Just one last one, I realised after he had gone that the "repair" at the end of the channel is not a repair. The downpipe used to be internal but most people have blocked this and put an external one. Should I ask him to check that it is not cracked inside the internal downpipe, which would involve removing the "repair"? Or if the channel is well sealed, plus the zinc on the parapet is done and the render, does it not matter? Also, is it ok to have the internal downpipe sealed in like that? It is still open into the regard at the bottom. Should it also be sealed at the bottom?

Many thanks
Gill

 

[datarebal]

If possible move the outlet to the outside.

bonne chance

 

[GillObrien]

Just because I like to finish a thread. The channel is done, the edges as well. The render will be redone in a couple of weeks. We decided to have it done properly in zinc so it could all be done at the same time, and they could create a fall to the downpipe.

Massive storm this week, nothing moved and no leaks .

 

[GillObrien]

To close this completely. The walls are now done. A previous repair on the gable end was done using silicone in the cracks, hence the leak. There were quite deep holes to be filled with cement and then it was properly primed, followed by the crepi. The colour is a bit different (I already tried to get a white colour before but apparently it is "out of fashion"). I will see how it looks after a few weeks and possibly paint it when we do the chimney etc.

Thank you all!