Hi, I have noted some thoughts on your plans below, hope this helps...
1) Dig a trench for 200mm x 100m sleepers. The bottom sleeper will be halfway underneath the ground.
2) Lay the bottom sleeper course on compacted gravel base. Should I put a rebar through or lay them on concrete mix for fixing them in?
- personally, I would raise the compacted gravel bed up to ground height rather than half sinking the bottom sleeper, to prevent it rotting from below. It doesn’t need a concrete base, in fact that would move and crack as wood will expand when wet but concrete doesn’t.
3) The rest of the courses to be laid with staggered joints (brickwork style) and screwed with stainless steel screws.
- fine
4) Line the inside of the retaining wall with membrane and backfill with gravel to avoid soil contact and help drainage. Would that be enough or do I need to install french drain pipe as well?
- fine, I don’t think a french drain is necessary but if you are worried a line of seep holes drilled through the bottom sleeper, would be sufficient.
5) To prevent the brick wall on the left and fence on the right from damp/rot, I'm thinking of building a u-shaped retaining wall keeping it flush with the gabion at the back. I plan to leave a gap of about 100mm between the brick wall/fence and retaining wall and put some gravel in that gap to make it look tidy. Is it a good of doing it? Open to suggestions on this.
- it is usual to leave a 100mm channel between a raised soil level and a building to avoid breaching the dpc of the building, so your instincts are right. But, if the wall is just a garden wall, with no structure attached the other side, I think Owd Potter’s solution of bitumen paint or such is sufficient. If it’s not your wall, but your neighbours, you may want to explain what you are doing to protect their wall.
The fence is more vulnerable to rot and also pressure from the weight of raised soil against it, so yes needs protecting. Again, gravel boards cemented in, in front of the fence should be sufficient, if you can get them high enough. If not, you could cement in a line of paving slabs to achieve the separation, or just build a short wall in front to contain the soil of the new raised level.
Thanks for the time you've taken to review my post and reply. So what depth would you suggest for the trench or compacted gravel for a 600mm high wall? Just checked the concrete gravel boards, they're available at 300mm high. Can you please advise on how to fix them against the existing fence? And is there a way to stack 1 on top of the other to get the 600mm height?
I'm quite hesitant with the u-shaped wall as well for it's extra work & money. But just thinking of ways to save the fence. I like the idea of painting the brick wall with damp proof paint. When you say fill with granular fill as retaining wall, do you mean fill the left side along the brick wall as well? Would I then need to secure a membrane to hold the fill in place? How much thickness would you recommend for the fill? Yes, granular fill immediately against the wall to about 150mm width should suffice, no extra membrane would be required to hold it, just raise the granular fill as you do the general earth backfill to raise your level. The intention is simply to create a free draining plane behind the wall so that water is not held against the wall within waterlogged soil.
I got a couple of quotes to build the retaining wall (just the horizontal one not u-shaped), steps and turfing the upper section around the £3k mark including labour & material. It's a lot of money, so I want to do it myself, hence carefully planning things in advance.
Yes, that is they. Use one on every other course short limb screwed to rear of sleeper and long side to brickwork.
Ya fence is tricky, just concerned if your proposed L-shaped retaining wall (sleepers in the middle and along the fence on the right) would look aesthetically pleasing!! If I go with steps on the right, would they be enough to cover the raised soil along the fence? The current steps go 1200mm deep for 600mm high wall.
I'm not suggesting an L shaped retaining wall in sleepers, they are an expensive material to use for a hidden wall. But you need to create perpendicular returns to stabilise the front retaining wall and your plan to put steps centrally will serve that purpose. Against the fence, I would build that part of retaining wall in 100mm dense concrete blocks and secure end of sleeper wall to it with straps as with the wall on left. Where you site this, whether immediately adjacent the fence (as I would) or 100mm from it creating a void is at your preference.
Apologies for throwing so many questions at you. Just want to make sure I cover my base before putting the shovel in the ground.. Thanks
For the compacted gravel base, it doesn't need to be very deep, 20cm maybe... the weight of the stacked sleepers themselves, especially if laid face down, will hold them in place.
600mm, ok, maybe you could stack two gravel boards one on the other, the bottom one cemented in and the two courses held in place by hammering in stakes/rebar between fence and boards, to a height short of the top level so they are invisible. Im not really sure how well they would stack though, it’s a while since I have seen a gravel board! There are many ways you could do this, if it were mine I would build a narrow blockwork wall, perhaps neatly topped with a row of stone tiles or granite setts to finished soil level - also for ease of mowing if you have a full width lawn as you can run the mower over the tiles.
I think there gets to a point where you can overthink and overcomplicate it, sometimes you have to just go for it!
Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
For the compacted gravel base, it doesn't need to be very deep, 20cm maybe... the weight of the stacked sleepers themselves, especially if laid face down, will hold them in place.
600mm, ok, maybe you could stack two gravel boards one on the other, the bottom one cemented in and the two courses held in place by hammering in stakes/rebar between fence and boards, to a height short of the top level so they are invisible. Im not really sure how well they would stack though, it’s a while since I have seen a gravel board! There are many ways you could do this, if it were mine I would build a narrow blockwork wall, perhaps neatly topped with a row of stone tiles or granite setts to finished soil level - also for ease of mowing if you have a full width lawn as you can run the mower over the tiles.
I think there gets to a point where you can overthink and overcomplicate it, sometimes you have to just go for it!
Ya I think I just have to order materials & get to it now. I'm sure lots of different thoughts and ideas will keep coming to mind. Would probably go with a block wall next to the fence. Would just have to see some videos to make sure I can do it myself. Would there have to be deep foundation for the block wall?
I'm not suggesting an L shaped retaining wall in sleepers, they are an expensive material to use for a hidden wall. But you need to create perpendicular returns to stabilise the front retaining wall and your plan to put steps centrally will serve that purpose. Against the fence, I would build that part of retaining wall in 100mm dense concrete blocks and secure end of sleeper wall to it with straps as with the wall on left. Where you site this, whether immediately adjacent the fence (as I would) or 100mm from it creating a void is at your preference.
I'm getting inclined towards block wall along the fence as I agree it will cost a lot of money to build retaining wall along the fence for it not to be seen at all. I just need to see if I can do the blockwork myself. Thanks for all your help and guidance. Really appreciate it. Will hopefully start on the project soon and update here when I've made some progress..
The depth of the foundation depends on the width/height of the wall and how stable the ground is, but generally speaking, for a simple retaining wall, 30cm depth should do it - but it needs to extend out either side of the wall as well to create a stable platform (so the wall on it’s base is like an upside down T shape) roughly the width of the block, so if the blocks are 20cm wide, it needs 20cm base either side. This will leave hand space for you to work as well. The capping tiles can extend to fill most of the gap left between fence and wall, without actually touching the fence, for a neat finish.
Laying and mortaring the blocks is pretty easy (no need to worry about neatness of mortar as it will be hidden), the main challenge is measuring and remeasuring and using a plumb line and spirit level as you go to get it straight and not leaning. Lots of good videos on youtube, but some good info here:
https://www.diydata.com/techniques/brickwork/foundations/foundations.php
Don’t be scared of it, take your time. Good luck!
Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
Posts
Just checked the concrete gravel boards, they're available at 300mm high. Can you please advise on how to fix them against the existing fence? And is there a way to stack 1 on top of the other to get the 600mm height?