Path above damp proof level.

[Camdrill]

Neighbour has laid a patio alongside my house where top of slab is level with my dpc . He has laid a 100mm linear drainage channel between the slabs and my wall. Is this ok?

Thanks

 

[trowlerman]

Not ideal , but with the shingle should be ok

 

[Joe Malone]

I don't agree that with shingle it should be OK. It won't be ok and effectively your neighbour has now bridged your DPC. You have 2 issues, 1. Inadequate wall base ventilation and, 2. Rainsplash saturation above DPC level. The potential problem will be far worse if you are in a solid walled rather than cavity walled property since there is a far greater potential for wall base damp on the internal walls.

In essence you have a case for statutory nuisance against your neighbour. The requirement for 150mm below the level of the DPC is a commonly accepted principal and in fact I am dealing with almost exactly the same case for a client whose neighbour has bridged their DPC with his drive.

 

[^woody^]

But it won't be a problem if it's a cavity wall.

 

[Joe Malone]

But it won't be a problem if it's a cavity wall.

Not exactly correct Woody. It won't cause internal damp so long as the cavity is not blocked or bridged but the DPC in the outer leaf is there to protect the building fabric. The outer leaf is at increased risk of spalling due to hydraulic frost action if the DPC in the outer leaf is bridged. Don't forget that the building regs enforce DPC installation in the outer leaf for a reason.

 

[^woody^]

I was thinking that it would not be a s82 problem.

But in general, the wall will be just as damp, (or dry) as it would when moisture runs down the outer skin and holds on top of the DPC.

The drainage channel installed at DPC height, implies that there is no significant persistent damp to the wall anyway, other than possibly a few splashes.

The traditional DPC in an outer skin of a cavity wall does very little, and I'd suggest it could well be redundant and a relic from the days of solid external walls. Whilst building regs may enforce it, it can be easily demonstrated that it has little bearing on keeping the internal side of a cavity wall dry - which is what Part C is all about and where the requirement comes from. And I've argued that very point successfully with BCO's.

Any bridge in a cavity is itself a defect and should not be there. Such a defect is unrelated to any DPC being in the wall, so is not a reason for having a DPC in the first place.

So if the OP's wall is cavity, then this situation should not be an issue.

 

[Joe Malone]

I was thinking that it would not be a s82 problem.

But in general, the wall will be just as damp, (or dry) as it would when moisture runs down the outer skin and holds on top of the DPC.

The drainage channel installed at DPC height, implies that there is no significant persistent damp to the wall anyway, other than possibly a few splashes.

The traditional DPC in an outer skin of a cavity wall does very little, and I'd suggest it could well be redundant and a relic from the days of solid external walls. Whilst building regs may enforce it, it can be easily demonstrated that it has little bearing on keeping the internal side of a cavity wall dry - which is what Part C is all about and where the requirement comes from. And I've argued that very point successfully with BCO's.

Any bridge in a cavity is itself a defect and should not be there. Such a defect is unrelated to any DPC being in the wall, so is not a reason for having a DPC in the first place.

So if the OP's wall is cavity, then this situation should not be an issue.

I've no doubt you have argued and won the case with a building control officer Woody but he was wrong to agree and should have known and understood the building regulations better. Resistance to moisture is also about protecting the building fabric and if you understand the concept of hydraulic frost action then you should understand why the physical DPC in the outer leaf is far from redundant.

 

[loply]

If you fill a cavity wall with blown-in insulation, does the insulation move moisture from the outer skin to the inner?

Or in other words if the OP already has it, is this more of a problem?