4 x patio questions

[neiloneil]

My mum was quoted for a patio. I want to check if the procedure that was outlined sounds ok

1. I have an existing patio which I want to extend to double its size. Can I use it as a base for the new patio? If so, how much of a mortar bed should I allow?

2. Should i dig out the additional area to 75mm below existing slab level for type 1 (compacted)?

3. is 4 sharp sand to 1 cement, semi dry mix ok for bedding new slabs over existing slabs?

4 The new patio level will be raised to 2 to 3 inches below the dpc. If i put a french drain between the patio and house, how wide and deep should it be?

 

[neiloneil]

I have answers for the first 3 . which are yes, yes , and yes.
Any advice please on the 4th?
The new patio level will be raised to 2 to 3 inches below the dpc. If i put a french drain between the patio and house, how wide and deep should it be?

 

[Halitosis]

First three sound like a decent professional job.
I have done similar to point 4, with a 6 inch wide gully adjacent to the house (OK its closer to 5 inches but was meant to be 6), leaving it at the same depth as the original ground level (which is presumably well below the DPC). This meant building a dwarf wall to support the patio - easily done with a row of cement blocks. You should ensure the base drains reasonably and doesn't leave a 'moat'. Many folk like to fill the gully with pebbles but then you end up with crud building up at the bottom, and you can't see if its clear and dry. We long since forgot our gap is there. Of course the gap can be breached at door thresholds.
Edit - hopefully this image appears and helps