Cavity wall: inner leaf DPC lower than outer leaf DPC - to what extent is this OK?

[lineweight]

The diagrams below are from Building Regs Approved Doc C.

 

The one on the top left shows the inner-leaf DPC a little lower than the outer-leaf one. It implies that this is fine as long as there's a clear 225mm cavity depth below the inner leaf DPC.

 

But how far can this be stretched? If that inner leaf DPC was at the external ground level, for example, then it appears that building regs are OK with it, but this somehow doesn't feel right. For example it would rely on a certainty that there was no bridging of the cavity in that 150mm zone of wall above the external ground level.

 

What's your interpretation?

 

 

Edited June 30, 2024 by lineweight

[lineweight]

No thoughts on this?

[joe90]

That’s the regs so I don’t see a problem with the outer DPC bring higher than the inner as long as the clear cavity 225 below the lowest.

[lineweight]

So, in theory can it be pushed down to the extent that the inner DPC is lower than the external ground level, as long as the cavity still continues 225 down below that?

[joe90]

9 minutes ago, lineweight said:

So, in theory can it be pushed down to the extent that the inner DPC is lower than the external ground level, as long as the cavity still continues 225 down below that?

I guess so.