Emanresu

Thanks for the heads up on the alternatives/ About 15% of the patio area is currently gravel on clay. We want to put slabs on this area which will further reduce the chances of the runoff draining. A suggestion from our usual builder (not the driveway guys) is to connect the current small (concrete?) gutter/soakaway which runs the length of the supporting walls with the main drains. Should the pooling/groundwater be sent to the drains or should it drain away to the sublayers using new 110mm holes?

Similar issue to this one https://forum.buildhub.org.uk/topic/39497-patio-issue/ Our late 70's house is built below a road and two levels of garden. There are retaining walls and steps up to the garden. Around the house is a slab patio which is in need to replacement. We have been reluctant to replace the patios due to the amount of silt laden water that comes off the garden each winter/spring. So the question is how to improve the drainage before we press the button and get the patio guys back in. The job they did on our driveway was first class but a lot easier to drain as it has a slight slope. The patios area are flat. Main issue is how to deal with the block drain holes embedded in the retaining walls. Can they be re-drilled or replaced. Secondly there is a small drainage area that is no connected to any drain and gets swamped with water when there is anything heavier than a light shower. Suggestions where to start looking to understand how to solve the issue.