Building an extension near the foot of a retaining wall

[Edward]

The land on our property is retained by a wall approximately 3m high, our garage sits about 1.5m away from the edge of the retaining wall. Our neighbours are proposing to extend their kitchen towards the retaining wall. Their land slopes upwards towards the wall. My best guess is that to get the necessary FFL in their extension, they will need to excavate 800mm down at the deepest point, ie the point closest to the wall. I am therefore concerned their construction could possibly cause settlement issues on our property as the foundations to the retaining wall may become undermined. Is there any rule/regulations or even guidance which covers the topic about building at the base of a retaining wall? As of yet there has been no planning permission application so there is no immediate concern, however I would just like to empower myself with this knowledge when the inevitable application does come in. I do not know how close to the wall they are looking to extend to. Thanks in advance.

[ProDave]

As they will likely break the 45 degree foundation of the retaining wall, you would need to invoke the party wall act and appoint a party wall surveyor to ensure their construction and any alterations to the retaining wall are properly designed and properly constructed.

[saveasteading]

9 hours ago, Edward said:

to get the necessary FFL in their extension, they will need to excavate 800mm down

Are you sure that is all? 

Floor, and insulation likely to be 300 thick, and foundations 900mm/1m deep.

Your neighbour has to organise all permissions.

https://www.gov.uk/government/publications/preventing-and-resolving-disputes-in-relation-to-party-walls/the-party-wall-etc-act-1996-explanatory-booklet

 

I found it amusing that this is published by the  dept currently called 'Department for Levelling Up'.

Not  'digging  down and undermining my house'.

 

[Rob99]

Definitely sounds like party wall legislation applies here.

 

Speak to your neighbour about it as they may not know. Lots of people think, oh it's my land and I have planning and building control permission, but don't always know about party wall stuff. It's worth remembering that all costs of surveyors etc for dealing with the party wall matters are your neighbours responsibility, including any surveyor appointed by you. If you can agree on a joint surveyor it's cheaper and easier all round (assuming you have a good relationship with your neighbour).

 

Also, I would make sure that whoever is doing the work carries full insurance as, if anything happens to the retaining wall during the works, your garden and the garage could end up in your neighbours garden!!

 

 

[saveasteading]

1 minute ago, Rob99 said:

whoever is doing the work carries full insurance

Good point. Many small builders have insurance found in the small ads in The Sun. The cheapest cover that can provide a piece of paper.

You need to see the actual cover details, not just a front certificate.

The exclusion clauses can be shocking. 

eg No works below ground level. No works above 3m. The policy holder only. No hired in machinery. Working under the supervision of the client's project manager.   etc.

You cant insist on seeing this as it is the neighbour's project, but you can perhaps help them along.

 

6 minutes ago, Rob99 said:

it's my land

That is what many people believe, and don't think they need permission in any way.