Just over a year ago I posted about rot in the snug. I think the problem was due to internal floor levels being up to 300mm lower than external ground levels. I was thinking about putting a proper French drain in.
It turns out there was already a proper French drain in place and the plastic pipe dates it to fairly recent, but it was completely clogged up with dirt. Another solution was needed.
We dug out the gravel from the French drain and a bit more soil, and put a concrete drain in the bottom with a bit of a slope. The original French drain emptied into a soakaway which was also blocked so we cleaned it out and replaced the pipe. Water doesn’t puddle in the trench and it’s 150mm to 200mm below internal floor level which should help the snug dry out.
Next on the job list is to build a short retaining wall to support the car park and fit grating on top to stop willow leaves from falling in. The trench will be ventilated to keep the walls dry, and should be reasonably easy to clear out when it fills up with muck.