Timber suspended floor patio level

[taylormsj]

Hello,

 

We have had a rear extension completed with external wall rendering and now I'm planning the patio outside.

 

We have rainwater sewer access at each corner of the extension so my plan is to run an ACO drain butted up against the external wall along the whole width of the wall. The patio would then fall towards the house so rainwater is collected by the ACO and run into the rainwater sewer. I have attached a mock up, showing the building, DPC and our desired patio height.

 

I asked our building control officer about how high the patio could be in relation to our internal floor and DPC. She has come back to say that the regs say 150mm below DPC, but there are work arounds with this when you have external render on the walls and ACO drains. However, she has said that because we have a timber suspended floor, the patio height can't actually exceed the concrete base that our floor sits on (as demonstrated in the drawing attached). The reasoning behind the patio not exceeding the internal concrete base is that water will naturally pool internally if the external ground level is higher (although I'm not sure how if the drainage is properly installed). This will result in quite a high drop between internal/external floor. 

 

My question is - are there any solutions around this to avoid such a steep drop from the house to the patio that will also satisfy building control? Our BCO has generally been very good and helpful so far, so I'm not sure if she was simply answering my question about my proposed solution without giving me an alternative, or if there actually is no alternative solution.

 

 

Thanks for any help or advice.

 

 

 

Edited July 16, 2021 by taylormsj
Replaced drawing