Height of DPC on outer leaf of cavity wall

Apologies for the appalling sketch but my 4 year old is out playing so I'm unsupervised.
Does it matter where the DPC on the outer leaf of a cavity wall goes?
I know it's usual to keep it level with the one on the inside and have any hard landscaping 150 mm below but I'd like to have the exterior paving level with the door thresholds all around an extension for wheelchair access.
Is there any reason why I can't simply place the outer leaf DPC 150 mm higher than the one on the inside to achieve this?
I could then raise the ground level up to door threshold level.
Thanks in advance

Its probably me but i dont quite follow what you want?

Anyhow, when using B&B, even in an extension, its necessary to have a detailed drawing with all the details expanded and finalised. B&B can pose a rake of hidden difficulties for the unwary.

External skin DPC's should be 150mm above GL. DPC's should be level across both skins.

Although ramps that dont simply bridge the DPC can be detailed into a new build it requires a detailed section view drawing from GL to threshold & FFL.

There are lots of pics of B&B on google and perhaps pics of ramps and steps that lead in to a threshold?

Thanks Ree I think you've answered the question.
DPC mst be level across both leaves.
I thought I could maybe cheat a bit and have the outer leaf DPC 150 higher than normal in relation to the inner one.
Then I could have the finish floor level and the paving outside at the same height all the way around the extension not just at door thresholds.
Looks like I'll have to use ramps at the thresholds then.

In consultation with BCO you might get a free pass and an allowed variation? Talk to them.

Just a thought: does RM42 and a white lanyard ring a bell? If not, please ignore this.

With all due respect to Ree suggest you ignore his post. Your drawing is half right but not quite correct,
It is standard practice on BB floors to have a split level DPC. The internal floor level causes no problems but external path can be troublesome. You are showing no DPC membrane on top of BB, no insulation or screed..Addng this on will drop BB down a further 150mm below finished floor level
You require 150 clear air space below bottom of beams and sub site to allow for ground heave. Cranked air bricks, number of, all as required by BR.
Run a dry 112mm DPC under beams and a 300mm wide DPC on top of beams and under block wall.
Lay your DPM tight to walls but underneath the 200mm of DPC sticking out from block wall . Tape the two together Lay insulation, tape joints, lay on top any first fix services that you require in pipe in pipe Lay fibre screed..
You require a mobility door and frame make minimum opening door size 838mm wide other wise you hit your knuckles on door frame.
Thats all for now be back within two days for external path details etc.
Regards oldun.

ree said:

In consultation with BCO you might get a free pass and an allowed variation? Talk to them.

Just a thought: does RM42 and a white lanyard ring a bell? If not, please ignore this.

Click to expand...

Yes but it was a little while ago.