Land drain or channel drain into old clay - Advice needed

[dogsdinner]

Hi after cribbing lots of great advice from the site I was hoping to get a little more. Apologies for the long post.

We have an 1850s victorian terrace. We are on clay but mostly seems to drain ok. At the back (rear is a 1970s extension) I noticed some damp in the wall and spotted the patio is only about 20mm below DPC so maybe splashback.

I've dug out a 2ft deep trench along the extension footings and was considering putting in either a land drain or a channel type surface drain. Helpfully there is a kitchen waste about half way along the wall and a rain gully (going into combined FW and SW) at one end.

However when I dug down, the kitchen waste is into a 1 and 1/4 inch copper pipe (which is leaking a tiny dribble where the plastic waste downpipe joins) and the rain gully is old clay, almost fully encased in concrete.

I think it would be easiest to simply fit a channel drain near the surface as it looks like it would be easy to jury rig this into the existing rain gully and get the necessary fall. But maybe prefer the idea of burying a land drain, running along the wall lower down in the trench to absorb any moisture from the house wall. But to get the fall, I'd have to smash out the existing gully...

So the questions are -
- land drain or surface channel drain?
- how should I connect to the existing clay?
- IF a channel drain, should I still sit it on a deep bed of gravel to ventilate the wall - or will this become a moat?
- If it I don't use gravel but instead use concrete, then how will the wall still 'breathe'?

Thanks in advance.

[dogsdinner]

Here is a photo of the clayware

[seanandruby]

I'd go with the channel and in line gully if you can fit it. but if you can't you can use the old gully with a sleeve to connect and seal with a 1x1 sharp sand cement mix, lay channels on concrete.

[dogsdinner]

Thanks for that. Defo no to the perforated land drain and gravel idea then?

Cheers

[seanandruby]

No, you want to get rid of water land drain will encourage it.