Patio drainage with retaining wall

[JamesBuild]

Hi All,

New poster here.

I am building a new patio that slopes slightly away from the house and leads to a step up to where the turf starts. The pic below shows the first area where the existing patio was and then a trench where we are going out further than the original patio and will need some extra aggregate.

As the turf starts slightly higher I was going to build a small step up to the garden however I am worried this will lead to a build up of rainwater on the patio side of the step. The garden is enclosed by two concrete fence foundations so nowhere to escape on the sides.

Some have suggested a french drain however I am unsure where this would lead to because of the lack of a drain in the garden.

Does anybody have any tips for drainage in this situation? I dont have access to any drains in the garden.

Many thanks!!

[ToughButterCup]

Build the wall and the step(s)

Make a little trench (200mm) between the steps and the lawn , fill with 10mm /20mm if you'd prefer to (say) 400mm .

[JamesBuild]

Thanks, and regarding subbase can I lay an MOT 1 subbase on sand or does it have to be on soil/clay?

 

Thanks

[Temp]

No rainwater down pipes you can connect into? What is the soil type? Do soakaway work on your soil?

 

A French drain used as a soakaway on the patio side of the wall would need to be rather deep. Not sure it's a good idea so close to the retaining wall founds? We used a linear drain but we have drains it could connect into.

 

You can put MOT 1 straight onto compacted soil. I'd go for about 150mm, 200mm better. Compact soil first, then compact the Mot in at least two layers. We hired a wacker plate. 

 

[JamesBuild]

Nope no rainwater downpipes. Its clay, I think a soakaway may work but would have to be quite far away from the walls on either side so would be a big job.

 

Regarding the base I have dug down and its a thin layer of sand under what was a block paved patio so I wanted to lay the MOT 1 directly onto that rather than having to dig it all out!

[Nickfromwales]

Finish the patio 200mm from the up-stand wall at the turfed area and fill it with 3/4 decorative chippings. I think this will need to be around 300mm deep to be effective as a mini soak away, meaning you’d need deeper foundation for the wall. 
You defo don’t have any storm or foul drain at the rear?

 

Don’t worry about the concrete gravel boards each end, they’ll not stop water getting to the permeable part of the ground, plus with a linear mini French drain as above the whole length will catch / attenuate the storm water. 
Does this have history of flooding at all, in very heavy downpours?

[JamesBuild]

Its a house that has been cut into two so I think the storm drain might be in the other property. The old block paving patio didnt suffer any drainage issues so I think it should be ok. 

 

I think I will just dig a deep trench as you say and fill with gravel to at least allow some sort of run off. 

 

You mentioned you would use a wacker plate for the soil before the MOT 1. I guess if I just have clay and some sand left over from the block paving would a mix of the two suffice if packed down enough before the MOT1?

 

Thanks!

[Temp]

5 minutes ago, JamesBuild said:

You mentioned you would use a wacker plate for the soil before the MOT 1. I guess if I just have clay and some sand left over from the block paving would a mix of the two suffice if packed down enough before the MOT1?

 

 

Should be fine.

 

The compaction of the soil is because invariably there are some spots that are soft because you had to dig or rake to get it level.

[Nickfromwales]

3 hours ago, Temp said:

 

Should be fine.

 

The compaction of the soil is because invariably there are some spots that are soft because you had to dig or rake to get it level.

+1, just don't go mad with the wacker!