Boundary wall with insufficient foundations

[5lessmins]

We live on a bit of a hill. Our ground level does not rise for nearly 3 meters from our back door - so for 2 meters there is a difference in ground level of about 40cm between us. We have just removed an old rotting raised bed to reveal the foundation of the neighbour's wall. My neighbour has built (diy'd) a 2-metre high wall using our raised bed as the foundation/retaining wall - the concrete foundations only go down about 25cm - the wall is not safe it's sitting on exposed sandy soil on our side - it was never safe the raised bed was rotting wood and loose soil. I know the neighbour will be very upset about her plants getting disrupted, every interaction with them has been challenging. It's not about who pays - it's their wall and it's not safe and when it rains it's going to come down potentially on top of someone.
I feel quite anxious about this whole thing and whilst typing I know how desperate this sounds but is there some way you can reinforce a foundation after a wall has been built? Or will it have to come down and be built again properly?

Can you do a diagram @5lessmins, it's quite hard to visualise what you mean and where everything is?
I assume from your description that your garden slopes down to the neighbour's wall, is that right? Do people - in your or their garden - spend much time near the wall? I'm just thinking if you are right and it's going to come down so easily how likely is it that someone is going to be unlucky enough to be next to it when it comes down?
If neighbour is unfriendly and unlikely to listen maybe the wall falling down is how they are going to learn that they made a stupid mistake. Obviously you don't want anyone to get hurt in that process.

Thanks -. Yes people need to walk past the wall to get to the garden - it's at our back door - we are very close to it.

Can't easily draw the situation - I'll try to explain it again - we're in a terraced house - our back doors are at the same ground level - our gardens are on a slight incline - they have dealt with the incline very close to their back door with steep steps. Ours is dealt with about 3 metres from the back door but we had raised bed between us and our neighbours - so it probably looked like to him we had the same ground level as them. But the raised bed was loose soil and rotten wood - it needed to come out.

We have clearly made the problem more immediate but it wasn't done right in the first place.

Yes in theory, that’s what underpinning a house with subsidence is about. But probably easier to take down and begin again. You could do with a structural surveyor’s advice. So it would be worth looking at your house insurance 1) will they pay 2) will they pay for legal action against neighbour to recover costs?

Go to the council and report it.

It's hard to visualise - do you mean they actually built a higher wall on top of your boundary wall? Surely not?

Hard to draw with going 3d.

When you come out of our house there's a 5m by 3m level area (a) before the next level (b)
When you come out of their house there's 0.5m by 1.5 level area (a) before it steps up to the level (b).
They get up to level b very quickly and because we had a raised bed it looked like we had come up equally quickly.
So neighbour didn't realise their levels were not the same as ours. Their steps are very shallow and steep.

A - concrete foundation
B - Soil
C - Our ground level

It's very difficult to advise without being a) a professional or b) actually standing next to the wall. I think you need to get a builder in to look.

From my experience of having lived through an extensive house renovation for the last year it's always best to rebuild, but if you have difficult neighbours it might be best to try and have it shored up from your side just to stop it collapsing. If it does collapse you want it falling on their side at least.

If it does collapse you want it falling on their side at least.

I definitely don't want it falling on my side! Putting a wall up when you have no experience is a risky business. We have contacted a surveyor for advice, I think it's likely that it'll have to be taken down and rebuilt - we can offer to get it done from our side saving the plants - I hope they are not so unreasonable and will agree to this.
When it comes to safety we won't argue - we'll pay for the replacement - rather that than someone gets injured or worse.

If reasonable discussions with your neighbour, don’t work, you can report it to your local council via the gov.uk website:

www.gov.uk/report-dangerous-building-structure