Stepped Pitched Roofs - how are they built?

[Ivor Windybottom]

Adjoining houses going up a hill, House A (left) is lower than House B (right), as shown...

House A has damp on an internal wall. Is my guesswork doodle below an accurate representation of how this would be built?

...if so then surely this is asking for trouble, as the internal wall becomes external above their roof, so will always be vulnerable?

Also where is the boundary? I'd suggest it would be the cavity, in which case House A is responsible for that external wall, the flashing and arguably six inches of the edge of the higher roof.

Alternatively, perhaps that wall is the external wall of House B, in which case the boundary must be staggered if the same wall is House A's internal wall.

Or perhaps this isn't how they're built at all, and there are three walls (I doubt it). Built about 2000-ish.

All input welcome!

 

[Harry Bloomfield]

The horizontal arm of the flashing - in your drawing, should be above the tiles, not below..

 

[Ivor Windybottom]

Thank you, correct!

 

[Harry Bloomfield]

How can a builder, make a mistake like that?

 

[noseall]

The horizontal arm of the flashing - in your drawing, should be above the tiles, not below..

Not if its a soaker.

 

[Ivor Windybottom]

I'm guessing there (should) be a horizontal DPC at a point that segregates the inside from the outside. But running water is just going to run past that anyway, using the magic of gravity.

My relative's house is House B in this scenario. Next door is complaining, I'm trying to work out whose problem it is.

I think I'm going to offer to look in next door's loft, see if there's any sign of water coming in from the flashing above.

Detail of the flashing aside... is my doodle really how houses in this sort of situation are built? If so then that's quite unusual, the fact that the internal wall pops out in this way.

 

[denso13]

Detail of the flashing aside... is my doodle really how houses in this sort of situation are built?

Yes.

If so then that's quite unusual, the fact that the internal wall pops out in this way.

Not really, it would look the same for a single storey conservatory meeting a two storey cavity wall, for example.

I'm guessing there (should) be a horizontal DPC at a point that segregates the inside from the outside.

No, cavity trays are the norm, but not required here as the wall is not exposed.

 

[Ivor Windybottom]

Not really, it would look the same for a single storey conservatory meeting a two storey cavity wall, for example.
.

Good point. This house has a conservatory, there was once an issue with water getting in from the wall above when the rain was very heavy and driving from that side.

The houses are built from fake stone, I'm thinking it's possibly unusually porous. Makes me wonder what, if anything, they have done at the point where this internal/external party wall meets the front, it looks like the stone is just bonded as normal, as for any other normal corner, so there's a potential path from the front external wall into the neighbour's internal wall unless there's a vertical DPC but I suspect not. This corner is where the damp issue is.

 

[^woody^]

Normally there would be a stepped cavity tray. But that flashing arrangement does away with the need. It's not the most perfect detailing, as it does not allow for future potential roof leaks at the verge, but it's probably good enough.

Boundaries are vertical, not staggered.

 

[Ivor Windybottom]

Thanks, good to know that, according to my logic at least, we're never going to be responsible for the upkeep of that great wall of flashing.

Although I suspect this may be controversial.

 

[^woody^]

Thanks, good to know that, according to my logic at least, we're never going to be responsible for the upkeep of that great wall of flashing.

Although I suspect this may be controversial.

The flashing would normally be the responsibility and ownership of whoevers roof it is protecting.

 

[Ivor Windybottom]

It's arguably covering the external wall of House B (right) in my example, although it serves no purpose for them. If it was detached then it would have the same wall without the flashing and be absolutely fine and normal.

My conclusion is that it's entirely for the benefit of House A (left), and is well within their side of the boundary so is all their problem. But possibly they may see things differently.

Thanks for all the contributions. If anyone sees things differently please say, differing opinions welcome.