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Earlier in the year I employed a contractor to replace the lead flashing around my chimneys - ironically I had previously contracted someone else to do this and they had done such a bad job I needed to redo it. They also repointed and reflaunched the chimneys too.

Prior to having the job completed it was quite obvious that the chimneys had been leaking, there were obvious signs of water ingress around the chimney breasts. A couple of months after the job was finished and I had repainted the area, I noticed damp spots appearing on my chimney breasts and tried to investigate why that might be so. After some consideration I'm not sure the issue is still the chimney: there may be other issues e.g. hygroscopic salt (it is an old house and at one point there would have been open fires) or render failure. However while investigating in the attic I discovered I could see slivers of light between the chimney stack brick and the lead flashing in a number of places. I link a video

https://streamable.com/sfj3ts

and attach a photo of some of these slivers.

Visible daylight through flashing

The question is, would this light be 'normal' or cause for concern? The extensive YouTube research (!) I have done on chimney flashing suggests that most people fix the horizontal edges of lead between bricks actually in mortar, but the vertical edges are effectively 'open' which could mean light would be visible? I'd like to think my contractor has done a good job, but do not have the experience levels to tell.

For reference here is an external view of one of the chimneys taken by the contractor just after he had finished:

External view of chimney

NB - For background I'm not sure the damp spot issue is the water coming via the chimney stack anymore as there are also similar damp spots away from the breast on adjacent external walls; not really a question for this post just including for thoroughness!

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    This isn’t my specialty, but at a bare minimum, I think there should be some caulking/sealant at the vertical gaps. I don’t really understand why those verticals weren’t bent into cut gaps in the mortar. Jun 9, 2023 at 14:09
  • Certainly the tan mortar(?) seems to be very sloppily applied.
    – Armand
    Jun 9, 2023 at 19:57
  • Doesn't matter what it is, unless it's a window. If you can see daylight there's infiltration.
    – Mazura
    Jun 10, 2023 at 1:02

2 Answers 2

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I am not an expert on brick chimney flashings. If this is horizontal then there shouldn't be daylight like this.

But it would be difficult to install flashing on a rough brick surface and make it look tidy. So, I would expect vertical flashing to have gaps. Normally, very little water will get in and the design of the house should ensure that it does not come into the house.

In NZ, from the brick onwards, there is an airgap, followed by a sheet of building paper to stop ingress of water. If you have something similar, it should be fine.

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I'm not a professional but to me that flashing is pretty obviously no good. (see update below)

It looks to me like you have one piece of metal that was bent into a stair-step pattern with additional tabs of material on the horizontal "step" parts that was bent over and inserted in between the bricks. The foremost problem is that the vertical part is not sealed up in any way as can be seen from the first photo that shows the light. Any water that runs down the vertical edges can get in between the metal and the brick and will just flow inside. But even if you seal up those gaps, the caulking will fail pretty quickly and the problem will come back again. The way that this flashing is designed is the problem.

There would have been 2 (at least) good ways of doing this:

  • Cut a straight diagonal slot into the bricks. Make the metal straight and bend over one edge to insert into the slot sealing it with caulk or mortar. No gaps, everything is (ideally) sealed. Like this: straight flashing
  • Have a stepped flashing a bit similar in appearance to what you have there but each step is a separate piece of metal and the top one overlaps the one below it but a few inches. This way the vertical edge is still open like yours but when the water gets in it just run out over the flashing piece below it (unless there's a driving wind strong enough to move it past the overlap). This is the feature you're missing. Like this: stepped flashing

There is also the matter of setting up flashing and counter-flashing but I don't know what to do with that on a tile roof. Generally you want metal arranged such that it guides water down and sheds it away by overlapping in the proper way. You could probably arrange a flashing such that you see sunlight through some gaps and the water is still kept out but what you're showing is not that.


Update: I did some quick research on UK step flashings and they just don't seem like they would keep all the water out. The entire country can't be doing this wrong so they must work but I just don't see how so maybe I'm just clueless. I guess I should take back the "pretty obviously no good statement" above. I might need to post my own question about this. I'm captivated by this concept.

The soakers underneath aren't fixed to the wall at the top edge so they wouldn't deflect water coming down and the inside corners on the step flashing just look like they would catch water drops. What I will point out is that having the vertical part at a slant should help channel water away. Also this video was pretty instructive but I also note that the space around the chimney does look like it got water and the old flashing was not 100% waterproof. That might be because it was old but could just be the nature of the flashing. It may actually be designed to keep most of the water out and breathe enough to dry.

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  • I really appreciate your answer and photos (so much so I've upvoted); however I think there is a difference in how the building trades operate in different countries. The method of using one piece of lead cut into a step pattern is very common in the UK, looking out of my window I can see lots of similar flashing. Here's one example: youtube.com/watch?v=NWMkJ_M34B4. In no way saying you are wrong, but this method does seem very common here. What I'm not so sure about is whether the vertical edges are less watertight on my build than others! Jun 9, 2023 at 16:48
  • Love the video but only had time to skim it. It looks like he actually already has overlapping short segments of flashing running diagonally into a groove in the brick (sort of a combo of the 2 methods i listed above) and he's putting the stair-step lead over that. The stair-steps get rid of most of the water and the little that gets through is shed by the overlapping pieces underneath. Since you can see light up through the steps in the stair-steps, it seems like you don't have that lead underneath. Jun 9, 2023 at 16:58
  • Not supposed to score the actual brickwork in the UK, only the mortar.
    – Tetsujin
    Jun 9, 2023 at 17:19
  • @Tetsujin That sounds like a good policy. I'll watch that video carefully when I have a chance to try to figure it out. It may not bend into the brick but there has to be something underneath the stair-step lead because I just don't see how water doesn't drip into the inside at the corner between the vertical and horizontal edges. Jun 9, 2023 at 17:26
  • such overlapped step flashings work well. they work on the principle that water prefers to flow downwards instead of horizontally, roof tiles work on the same principle.
    – Jasen
    Jun 10, 2023 at 21:22

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