patio less than 10mm away from DPC

[zarinstclare]

Hello everyone, I'm becoming increasingly worried about a project I'm working on. I picked up the project halfway through, and the plans had already been made by a much more experienced builder than myself, so I just followed them.
I extended the air bricks under the soon-to-be tiled patio and installed a threshold drain around the house. My concern is that the level of the patio is less than 10mm away from the DPC. I was led to believe that installing a threshold drain was satisfactory to bring the patio to this level. However, as far as I have found in my research, having a threshold drain is irrelevant to the distance you can put a patio below the DPC.
Can anyone shed some light on how I may be wrong and the original builder might be right? Or, what the reality of moving forward with this would actually be? In other words, what is the real risk to the property if I continue with the current plan?
Thank you in advance for your help and expertise!

 

[George_engineer]

Minimum should be 75mm, generally 150mm.

Could you lower a 200mm section adjacent to the wall to that level?

If it is a well built cavity wall then the risks are increased frost damage to the bricks (as they will stay wet due to rain splashback).

If the wall is a solid wall (or a poorly built cavity/filled with debris or some types of insulation) then there is an additional risk of damp penetrating the wall.

 

[^woody^]

The whole "150mm below DPC" thing is really a throw-back to the last century.

The patio level below DPC does not matter if its a cavity wall.

If a solid wall, apply a quality water repellant 4 courses high.

The surface drain only helps if the surface is running towards the building.

 

[George_engineer]

The whole "150mm below DPC" thing is really a throw-back to the last century.

The patio level below DPC does not matter if its a cavity wall.

If a solid wall, apply a quality water repellant 4 courses high.

The surface drain only helps if the surface is running towards the building.

Throwback or not it's still part of the Building Regulations. As I said it's only a frost risk in a well constructed cavity wall (bricks above DPC are not required to be as frost resistant to those below DPC) but the cavity could easily be bridged.

 

[^woody^]

Throwback or not it's still part of the Building Regulations. As I said it's only a frost risk in a well constructed cavity wall but that is not a certainty.

The requirement is to prevent damp from getting inside, there is no actual requirement for a 150mm gap to the DPC, as other options are available.

 

[George_engineer]

The requirement is to prevent damp from getting inside, there is no actual requirement for a 150mm gap to the DPC, as other options are available.

I didn't say it was a requirement - I said it was still part of them, i.e. given as a standard detail that meets the requirements of Part C.