Narrowest retaining wall options for hedge boundary

[flanagaj]

I am investigating retaining wall options for a wall that will be tight up to the field boundary which currently has a hedge owned by the neighbour.  Gov website clearly states that when it comes to hedging you can dig down and cut up vertically.  So not worried about digging roots up to pour concrete footings.  The main issue I have is that the wall needs to be as narrow as possible as we don't have much space down the back of the house.

 

Sleepers are narrow, and won't last and a six inch block wall will take up considerably more width.

 

As the wall is less than 900mm, I was contemplating pouring a cast concrete wall, but unsure how I'd go about designing it.  

[Conor]

Reinforced concrete wall with a wide footing is the narrowest option. 

 

What's the depth of soil to be retained and what's the height above ground you want the wall? How much room do you have for footings on your side?

[flanagaj]

31 minutes ago, Conor said:

Reinforced concrete wall with a wide footing is the narrowest option. 

 

What's the depth of soil to be retained and what's the height above ground you want the wall? How much room do you have for footings on your side?

When you say reinforced concrete wall, do you mean hollow concrete blocks with vertical rebar, or a cast concrete wall using plywood forms?

 

Depth of soil ranges from 300mm to less than 900mm

 

We wanted to run the drainage down the back of the property, so unless we move the drainage to the front of the house, there isn't a great deal of width for wall footings.  Width from back of house to boundary is 1.2m

[Conor]

Think this is probably something for Gus to comment on, I'm just an environmental engineer, not structural. Anyway...

 

No, poured RC wall. Specifically a cantilever wall. With a height of upto 900mm, and that close to your building, I'd be tempted to get it designed by your SE.

 

 

I'm also assuming that you are on the low side, and you're basically retaining the hedge?

 

Propose to them something like 100mm thick 35N concrete with mesh, tied to a 500*200mm footing with mesh as well. Basically it will look like an "L" in section. general rule is you start off with a footing width half the height of the wall. But it can be much more complex than that.

 

Ideally you'd run the footings below the depth of your drainage and other services, so the thickness of the wall or the width of the footings doesn't really matter. 

 

 

Edited June 25 by Conor

[JohnMo]

We did our retainer wall with timber strainer posts. About 8" dia. Highest point is about 2m, but post buried a metre or so deep in concrete. That's about a narrow as you will get!

 

[Russell griffiths]

Narrowest would be concrete posts and gravel boards, it will look a bit puke though. 
rsj and railway sleepers will outlast you and come in at around 175mm wide. 
 

metal sheet piles, with a timber cladding added to the front sounds ideal

very narrow, if the timber decays you can change it without disturbing the structural part, you could clad it in anything you wanted really. 
 

how about that rusty steel stuff with a coating on it. 
CORTEN. 

Edited June 25 by Russell griffiths

[flanagaj]

49 minutes ago, Conor said:

Think this is probably something for Gus to comment on, I'm just an environmental engineer, not structural. Anyway...

 

No, poured RC wall. Specifically a cantilever wall. With a height of upto 900mm, and that close to your building, I'd be tempted to get it designed by your SE.

 

 

I'm also assuming that you are on the low side, and you're basically retaining the hedge?

 

Propose to them something like 100mm thick 35N concrete with mesh, tied to a 500*200mm footing with mesh as well. Basically it will look like an "L" in section. general rule is you start off with a footing width half the height of the wall. But it can be much more complex than that.

 

Ideally you'd run the footings below the depth of your drainage and other services, so the thickness of the wall or the width of the footings doesn't really matter. 

 

 

Yes, we are retaining the hedge.  As a side can you tell me how the underground drainage works if you come directly through the outer and inner skin and then immediately go to vertical?  Our floor make up is 100mm slab / Dpm / 200mm celotex / 50mm sand blinding / 150mm hardcore.  If I add that all up, I get 500mm.  If I then start my underground drainage with an invert of 610mm, I am already deep and with a 24m run to the STP, I'll be too deep.  So I'm assuming that I can come into the house at a level higher than 500mm?

 

 

[flanagaj]

35 minutes ago, Russell griffiths said:

Narrowest would be concrete posts and gravel boards, it will look a bit puke though. 
rsj and railway sleepers will outlast you and come in at around 175mm wide. 
 

metal sheet piles, with a timber cladding added to the front sounds ideal

very narrow, if the timber decays you can change it without disturbing the structural part, you could clad it in anything you wanted really. 
 

how about that rusty steel stuff with a coating on it. 
CORTEN. 

I love the look of metal sheet piles just as they are, but I suspect I'll struggle to find a company that will do them.

 

I haven't ruled out RSJ with horizontal sleepers.  They should be quick and easy to install too.  

[Russell griffiths]

Have a look at the corten system can be diy, rsj in a hole with concrete and steel panels between them. 
very modern on their website. 

[Gone West]

I had a similar situation and used concrete posts and concrete patterned gravel boards, but it was only 10m long. I have another area about the same length where I am using UBs and oak sleepers.

[Temp]

14 hours ago, flanagaj said:

As a side can you tell me how the underground drainage works if you come directly through the outer and inner skin and then immediately go to vertical?  Our floor make up is 100mm slab / Dpm / 200mm celotex / 50mm sand blinding / 150mm hardcore.  If I add that all up, I get 500mm.  If I then start my underground drainage with an invert of 610mm, I am already deep and with a 24m run to the STP, I'll be too deep.  So I'm assuming that I can come into the house at a level higher than 500mm?

 

Perhaps I misunderstanding this but I think 600mm is about the minimum depth recommended for soil pipes.

 

If you must be higher.. Normally you must have a large radius bend at the bottom of all stacks. Think they give you a socket at about 350mm above their invert level. How high that socket can be depends on what you want to connect to it on the ground floor.

 

Things like showers on the ground floor mean you sometimes want to connect into the stack below floor level.

 

If you only have a WC on the ground floor I would work down from it's outlet to see how low you need the branch into the stack for that to be. 

 

[flanagaj]

18 hours ago, Temp said:

 

Perhaps I misunderstanding this but I think 600mm is about the minimum depth recommended for soil pipes.

 

You can go shallower, but I think you need to cap the pipe with concrete.

[SteamyTea]

On 25/06/2025 at 21:55, Russell griffiths said:

how about that rusty steel stuff with a coating on it. 
CORTEN

Remember this.