Retaining wall and extension

[al88]

The neighbours behind us are building an extension. It's awful for many reasons but at the moment I'm most concerned about the impact this may have on the large retaining wall between our two properties.

Their property is on ground approximately 2m higher than ours and there is a substantial retaining wall at the back of our garden, the top of which is ground height for them. (There is then a fence on top for their garden)

The corner of their extension appears to be within about a metre of the wall. It's difficult to tell exactly due to the angle and height.

I'm concerned this may have impaired the safety of the retaining wall. No structural survey has been undertaken and I have no way of knowing the effects of this build.

Does anyone have any knowledge of building near to a retaining wall? I'm going to call the council and my building insurance tomorrow but would like to be armed with some knowledge.

My knowledge is patchy but a retaining wall is entirely the responsibility of the person whose land it restrains because escavations. Escavations at your level are the ones that would cause problems so I’d expect you to need planning permission or structural work for future extensions, but not them.

Your neighbours should have had a conversation with you about a party wall agreement.

If the extension covers more than 50% of the garden then they would have needed permission, and I thought it was within a meter of the boundary but I thinknif it vines under permitted development they don't need it nor party wall agreement.
Who's wall is it? This is unusual circumstances and you should check with the building regs department which would have advised/approved of the foundations.

I think we need a diagram

We’ve just had building control out to check the underpinning of a wall between us and our neighbours as we are having an extension built. Neighbours are ok with it but they checked and wanted an engineer to sign off. Ring building control.

Thank you everyone for your replies.

I wasn't sure about the party wall agreement. From what I read I felt maybe it didn't apply but I haven't really delved too far into that yet so any knowledge on that would be gratefully received.

It turns out that this is covered by permitted development, but I think maybe the particular circumstances means that it shouldn't be.

I will attempt to draw and post a diagram

Get advice from Building Control. You can also ask for the structural plan of their excavations

Here's a side view.

And here's an aerial view.

I think if it within 3 metres of your property, they have to issue you with a notice of excavation. They can't proceed without your written permission. Google notice of excavation for more info

I would be concerned. Where I live there were some new houses built at raised level beyond an existing retaining wall. It was built years ago with just soil behind and then houses were put in. The pressure of the build eventually caused the whole wall to collapse in spectacular manner right into the road which caused part of the path and carriageway to be fenced off for a year!,

There were some rows over the issue as the houses were part of a small estate and the costs were supposed to be shared.....not great to buy a house and suddenly find they were liable for the wall collapsing. Clearly yours is more straight forward but you don't want someone else's garden collapse into yours.

When I saw the wall being rebuilt the difference was laughable. From a double skin wall with some reinforcing, the replacement had huge concrete pillars into the land behind. The stone wall at the front was purely decorative. I did chat with one of the workmen when passing and he said it was increasingly a common problem building on land behind walls which creates pressure over time that they were not built to withstand