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Solving drainage issues with sleeper retaining wall

mrsquaremrsquare Posts: 3
edited February 2022 in Problem solving
To set the scene: I semi-recently bought a terraced house that has a small rear garden consisting of two totally flat levels separated by a sleeper retaining 'wall' (more of a pair of steps, really). When I moved in, the upper level nearer the house was covered in concrete pavers (ugly/uneven) and the lower level in raised wooden decking (rapidly rotting). With our first kid on the way, my wife and I wanted an area of grass to use over the summer so I ripped out both of the above with the aim of laying some turf on the upper level and possibly paving (TBC) the lower level.

Before pic:


After pic:


Sleeper wall/steps close up:


Upper level is approx 4.2m x 4.2m, for scale.

So as you can see, I've removed all the decking from the lower level and the patio slabs (and underlying hardcore, cement, weed fabric etc.) from the upper level. I also topped up the upper level with a few tonne bags of soil (as it was several inches lower once the slabs were gone), and also gave the upper level a once over with a rotivator.

Since doing all of that towards the tail end of Autumn last year, the weather has been pretty foul and has highlighted that there is absolutely zero drainage on the upper level, which is something that I naively didn't consider before starting all of this! The bottom level seems to be naturally very free draining, but on the upper level rain water will now just pool and go nowhere - its particularly bad in the two corners near the sleeper well, but really the whole area just becomes a huge boggy mess every time it rains, and clearly I need to sort this out before even attempting to do anything else with it!

I'm a complete novice at this stuff, but its a fairly small area and I feel like it must be something I can tackle in my own, but I'm feeling a bit overwhelmed in terms of how to fix this, so would very much appreciate any thoughts from people more experienced in this sort of thing!

I'm bordered on both sides by my neighbours and I don't want to just dump a load of excess water onto their properties so I think I'm going to need to get it through/under the sleepers somehow. Could I drill some weep holes in the sleepers and be done with it, or am I going to need to get more involved and put in a french drain-style system? Or maybe both? Will either of those help with the water nearer to the house or do I need to run drains from the house down towards the sleepers?

Thanks!

Posts

  • FairygirlFairygirl Posts: 55,117
    You can certainly put in some drainage into the sleepers, but you would probably need some proper pipes put in, as the holes would close over time.
    However, if you're turfing/seeding the top section, the grass will naturally take up water once it's established. It's quite normal for a bare area of ground to look like that during winter, so it may not be as bad as you think it'll be. 
    While it's a great idea to prep the area for grass over autumn/winter, unfortunately it often means you have a sea of mud at this time of year, especially if you're in a wetter location. You may still need to add a bit more soil at the time of turfing/seeding because it will settle and sink a bit more. 
    Once you have the area grassed, you may find it gets very worn too, if you're accessing it directly from the house, but I understand the reason for wanting it when you have a wee one on the way. The consolation is that your neighbour on the left seems to have a decent set up, so you might be able to ask them what they've done.
    The grass might need regular spiking and aerating to keep the drainage decent too, and if it's a shadier site, you'll find it needs a lot more attention than a sunny one   :)
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
  • KT53KT53 Posts: 9,016
    Unfortunately for the OP, it would seem that the paved upper area was done properly with compacted hardcore etc beneath the slabs.  Even once that has been removed the soil beneath will have been heavily compacted thereby greatly limiting any drainage. 
    It would be a fairly major job, but removing the new soil from the last couple of feet near the steps and then breaking up the compacted soil below may help.  There would at least be easier drainage through that section.
  • FairygirlFairygirl Posts: 55,117
    I think the area was rotovated though, which should have made a huge difference. 
    I had to do something similar here, but fortunately, I didn't need to rotovate, as I was creating a raised lawn. The paving had been laid on the usual red, coarse sand, so it was relatively easy to amend by digging the sand into the clay below, along with the surrounding gravel.
    A few inches of soil is all that's needed for grass to do well, so as long as there's some eventual drainage, it won't necessarily be a major problem.  :)
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
  • LoxleyLoxley Posts: 5,698
    You need to remove hardcore from the previously paved area, and break up the underlying soil to restore some semblance of drainage.

    Dig a big trench at the back of the sleeper wall (drill weepholes along the bottom), line it with fleece-type geotextile, fill with clean stone, fold the geotextile over the top so that soil can be replaced over the top. It might be an idea to run a shallower trench around the perimeter of the whole area, linking with the the big one at either end. Allow 150mm of soil cover over the trenches.

    Your topsoil needs to be free draining, possibly incorporate gritty sharp sand, perhaps even a layer of pure sharp sand before laying the soil.
    "What is hateful to you, do not do to your neighbour". 
  • mrsquaremrsquare Posts: 3
    Thanks for the advice all :smile:
    Fairygirl said:
    I think the area was rotovated though, which should have made a huge difference. 
    Yeah, I went over the whole area with a rotivator after removing the patio last year as it was extremely compacted. At the time it made a big difference (visually, at least) but after treading it down (by foot) and then with all the rain, its now looking pretty compacted again! I read about rotivators potentially causing a 'pan' of hard soil which can cause drainage issues - could that have potentially happened here, or is that only if you seriously overwork the soil?

    Fairygirl said:
    The consolation is that your neighbour on the left seems to have a decent set up, so you might be able to ask them what they've done.
    You can't really tell from the photo, but their house sits slightly lower than ours and the grassy area is on a slope so they get natural runoff (although I have noticed it does get quite waterlogged on the border where their grass meets their patio). But yeah, it is quite a shady north facing area (in Scotland too!) but everyone around us has fairly healthy looking lawns so its definitely achievable.

    Loxley said:
    Dig a big trench at the back of the sleeper wall (drill weepholes along the bottom), line it with fleece-type geotextile, fill with clean stone, fold the geotextile over the top so that soil can be replaced over the top. It might be an idea to run a shallower trench around the perimeter of the whole area, linking with the the big one at either end. Allow 150mm of soil cover over the trenches.
    This is the sort of thing I was anticipating, yep. I like the idea of running it partially around the edges too. Would it be worth throwing a land drain in there too or is that overkill? My main confusion with this aspect, I think, is what happens to the water once its in the trench - as in, would it just dissipate naturally or does it need a proper outlet, but from the above posts it sounds like I'm on the right track with drilling some holes/pipes through the sleepers.
  • FairygirlFairygirl Posts: 55,117
    Smashing, aren't they, these spammers @pansyface. They must think our heids zip up the back!  :D
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
  • FairygirlFairygirl Posts: 55,117
    edited February 2022
    Sorry @mrsquare - I've just seen your response. It's always harder to keep grass looking decent in that aspect, but you can always go down the route of having a daisy filled area of grass, which is easier, and great for kids. It's quite difficult to be specific with drainage too, without seeing the site 'in the flesh'. 
    A hard pan of clay often happens simply because of heavy foot traffic [or machinery] and especially when there's been paving, but if you've rotovated, it should be possible to have grass, as long as you have  a reasonable layer of well drained material on top. I've done it without any problem. It'll certainly be rubbish just now though.
    If you could have seen the layer of compacted, sticky yellow clay I had when I was digging out the area for a pond last year [after removing the lawn I'd created there ] you'd know what I mean.  :)

    I'm afraid excess water is something you'll have to get used to , especially if you're in the west, although right now it's hailstones that are heaving down here   ;)
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
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