French Drain - depth, ventilation, soakaways

Partial answer - the pipe is perforated so water can seep into it... then you need to take the pipe to somewhere where it can empty to, ie a soak away. If you dont want to use a pipe it could just be a trench full of pea shingle or other stones/gravel... it's just a ditch into which water runs

1) No, the perforated drain will simply let water seep into it from the surrounding soil and carry it away. 2) A soakaway would be ok but bear in mind the area you are trying to drain- if it is a lot of water you expect to relieve from the ground, a larger soakaway will be required. 3) Yes, the slabbing will allow very little to no water to pass through it (if done correctly) and a slight fall would allow water to drain off the slabs. I would reccommend the fall just turn the bubble on a spirit level. 4) I would be worth adding an ACO drain at the bottom of the slabs (the lowest point of the patio) in order to carry the water away, or indeed add another french drain. An ACO drain can be easily connected to a perforated pipe but again, make sure it falls the right way! 5) 300mm is good but the pipe should be layed in the middle of it, not on top. Lay a weed-proof membrane at the bottom of your trench and drop some shingle/ stone in, then lay your perforated pipe in, making sure you have a rough fall toward your soakaway. Then cover in more stone/ shingle, wrap the membrane over the top and cover in soil ready to be turfed. If you want the stone exposed, just pop some membrane in the bottom to try and stop weeds coming through. 6) Anywhere between 1 in 100 and 1 in 150, so nice and gradual. If you are still unsure have a look on this website for some more tips and info, they offer good suggestions for soak aways, linking pipes and spacing etc. https://www.drainagepipe.co.uk/land-drains/land-drains-overview-layout-installation/ Hope this helps.

Hi With regards to your french drain This is the way i would proceed, if you dig out your required area for the french drain installation please make sure you dig the trenches approximately around 300mm wide, depth would be at least 300mm depending on the run distance as you would need to have a sufficient fall at least 1/80 once this has been achieved you would then need to install garden garden membrane into the trench and fill with at least 50mm of 20mm shingle, The pipe then goes on top of the Shingle holes face down and then add at least another 50mm of 20mm shingle over the top of the pipe, then wrap the membrane over the shingle, add another 50-75mm shingle over the membrane, top soil over this approx 50mm to ground level..The outlet would then either ideally discharge into a waste ditch or outside drain gully, this not being the case then a crate soak-away wrapped in membrane would have to suffice, i would also add an external vent pipe from the crates, make sure you also install a vent at the start of the pipe above ground level, hope this helps..