Are there any structural engineers around?

[Anotherdayanother2]

Mu garden is high at both ends and dips in the middle. I am in the process of levelling it out into one height (height mid way between highest level and lowest level and same level as semi-detached neighbour's garden.

Problem I have is that the neighbour's who live right at the back of the garden have built an outhouse right up to the boundary line of my garden. This has been there since I moved in nearly 10 yrs ago.

There was a brick wall right up against this building which served as my fenced which half collapsed a few years ago.

My landscapers today, when they were levelling the ground, found that the footing of the building is very shallow.

The neighbour's obviously knew there is an issue, as during the summer put a steel post/beam to pin up that wall internally and changed a flat roof to a sloping one (way before I did any sort of garden work).

I'm now not sure what to do. Should I approach said neighbour's and advise that they have very shallow footings and get them to sort it out in fear that the wall will collapse back onto us or even them. 2 put back a metre or so of dirt (a flower bed of sorts against that wall as a kind of supporting wall).

Semi detached neighbour next to me intentionally left her ground higher at that end in fear of the same problem.

I really don't want to be paying for someone else's building and I was in my rights to dig in my own garden, but am worried.

It is a block brick summerhouse.. when my landscapers tapped on the wall it sounded pretty hollow too.

Not a structural engineer but yes of course you need to let your neighbour know. Given that dropping your ground level will affect their building, I'm surprised you didn't even discuss with them before hand tbh. I don't know whether party wall agreements are required when doing boundary work that affects a non-habitable structure but common decency dictates that you don't do anything that affects the foundations of any building of theirs. Even if the footings were deep, by lowering your ground level you are reducing them.

Can you put up a retaining wall a few feet before the boundary and leave the ground level alone at the back?

I think there are a few things to unpick here. DH is a Structural Engineer.

The op is allowed to level her garden. It is not up to her to ensure someone else’s building is properly built. So yes, do tell them that the foundations are very shallow because they won’t withstand the changes in land conditions. It is their responsibility to ensure their building doesn’t fall over. You could ask a structural engineer to come round and evaluate it from your point of view. In addition, roofs weigh quite a lot. They might have increased the weight and caused problems for the walls. The weight of the roof could push the walls out.

Secondly don’t put the soil back against it. This is a weight and the building will not tolerate such a weight from soil. Obviously the building was not built with soil against it, so I think you should keep it clear. I know that’s not what you want to hear, but soil should not be piled against it. If there even is a DPC, (Cannot see one) piling soil against it would cause damp above the dpc. That’s best avoided.

Thirdly, lots of buildings are shoddily built. If you need a retaining wall for your soil, they are very expensive to construct. £1000 per m is common. You might be better off putting in railway sleepers to keep the soil off the building. That would be a lot cheaper. It means you lose a bit of garden but it won’t damage their building. Do talk to them though because this building needs some help.

I need to clarify. You can level your garden but not use the building as a retaining wall. You need your own.

I'm a geotechnical engineer. You are not meant to undermine neighbours foundations. A 45 degree line down from bottom of their foundation is generally considered an exclusion zone. But a 45 degree soil slope isnt usually stable in the long term. Can you not restore original slope and incorporate it into plans?

Isn't there a reasonable expectation that ground level won't go lower? Otherwise what's to stop me deciding to lower one side of my sloping garden to the same level as my house, which would presumably affect next doors house which is on higher ground?

Or is that the reason next door built their house a metre from our boundary?

Guymere thank you for the very helpful information. Do you know what sort of work the neighbour would need to undertake then?

To clarify I didn't undermine the neighbour's structure at all. The brick wall that was meant as my fence was falling down and so when my landscapers removed that for our safety- that was exposed.

Will go speak to them tomorrow.

NotMeNoNo I can restore the slope but it obviously was structurally sound in the first place hence the neighbours doing work on it during the summer.

Does anyone know if you are allowed to build right on a boundary line like that without planning permission? I've looked on the borough's planning portal and cant see anything

I'm not sure about planning for the outhouse, but do you need planning to alter the height of the garden by a certain amount?

Zandana123 you could be right. Looks like if you build 2 metres within your neighbours boundary then it only can be 2,5 metres high.

We had a similar problem OP when we moved in the old owners had made raised areas at the back of the garden using asbestos and corrugated metal to hold it. We think when they did their 80s extension they put all the soil in there.
The neighbors behind us had then built right up to the boundary ( in fact I think they took a bit as we seem further back).

When we moved in they complained about the soil Shankar their building even though we know it was there first. Luckily we were digging it out anyway. When we did their foundations are really shallow and there's holes near the top of the roof. Interestingly though they have never complained again not since we pointed out the building height and being on the boundary.

I’m struggling to visualise. Regardless of how crappy the neighbours building, you should not undermine it. Was your old wall retaining earth ie was there a ground level difference between front and back? You should maintain support to the boundary either with new retaining wall or a safe compacted slope.

www.boundary-problems.co.uk/boundary-problems/walls.html

NotMeNoNo in front of that building there was a brick fence that sat on top of the soil. Similar to Sickoffamilydrama previous owners did exactly the same of dumping their old stuff there and this brick fence sat on top. When I first moved in one section was already gone, then a few years later one crashed down so it wasnt holding anything up.

Sickoffamilydrama how did you identify that it was asbestos and once you moved the soil away did and showed the shallow foundations did you do anything else to support the building?

I would try and keep a slope there to maintain the support to the foundations that was there previously and re plan your garden. Will you be putting back a fence? You can't just dig vertically at your boundary without providing support to neighbours land.

There are restrictions on the height of eves and ridges close to boundaries. I assume though that as an out building it was built within permitted development and without the need for building regs/inspection.

The sensible thing would be for them to underpin the foundations to a sensible depth, it would be very (very very) neighbourly to allow them some sort of access before you finish your landscaping.

The neighbors wanted us to sort the soil as it was causing them a damp problem.

We offered for our neighbors to put guttering on and they actually came and were noisy when we didn't have a gate/fence so they know how the foundations are, and I kind of think if you are silly enough to go that close to the boundary especially against something then you lose the right to complain 🤷‍♀️

Anyway it's been like this for 6-8 years now and not collapsed. There is still a slight slope towards it.

I also checked planning and for the height & size of the building the neighbors should have got permission however they is no record of it.

It is up to the owners of the building to ensure it has suitable foundations and it is built to withstand what, reasonably, it needs to retain. It must have been built without any soil against it. Obviously piling soil against it means it will be damp.

No wall on top of soil is safe. Walls need foundations. So you can slope your soil or build your own retaining wall. You should allow your neighbours to come round and repair their building. Yes, it can be on the boundary and it’s a shoddy building. It should have been built to retain your garden, but it hasn’t been. It’s too late to go into that now but you can retain your own garden on your own land. But, suggest they improve their building by X date or you will install a retaining solution for your own land. Just make sure it’s designed to do the job and not collapse.

Thanks for all your advice. Went around to the neighbours today and at first they were blase about it saying it was just a shed.

However I asked if they could come around and have a look as then they could visualise and now seem to realise what the issue is. They will be asking a builder to come around to have a look but then it now impacts my turfing should they need access. It is the first time I have met them and they seemed lovely.

But it will annoy me that I will lose some of my land to reinstate a slop or build a retaining wall so hopefully they will just underpin it. How much work will that involve?!

I'm due to turf this week (turf and soil ordered). My ground level is now at the same height as my neighbours (this outbuilding cuts across both of our properties) and the slope that the left hand neighbour left is 15-20cm cm so I cant imagine that being substantial enough so something more needs to be done.

If anything the owners of the outbuilding realise that the previous owners have actually taken over land that didn't belong to them as there is any alleyway that runs from my neighbours to the right and had this not been exposed they would have insisted that it was all fine.

Sickoffamilydrama that looks terrible but gives me some comfort to hear that it is still up

I actually know my garden had the soil set up before the building was built as my elderly neighbor was a very good historian he also helped put the soil there and it was long before the house was sold to the neighbors who built the building.

You can also see the mortar hasn't been neatened up on our side but on all the other side's it has. You can see similar with the OPs so wonder if similar has happened.

Should have said there was correlated metal and asbestos against the building then the soil so I imagine the neighbors built against that which was a bit of an eye sore.