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Architectural services

Can a Retaining wall be used as the outer wall of an extension?

Anonymous user 16/03/2024 - 2.45 PM

Hi, We’re looking to extend to the rear of our semi detached bungalow. There is a yard area (3.5m x 2.5) with a stone wall on one side, a fence on the other and a 2m high retaining wall opposite the rear wall of the house (hope that make sense!). Can this wall be used as the outer wall of an extension if a tanking system, insulation and second block wall is constructed? Or would the outer wall need to be constructed separately? If separately is the a minimum distance that the new wall has to be from the retaining wall? There’s not much space to extend into and want to maximise the internal space as much as possible! Thanks in advance for any replies. Thanks for all the responses - if the retaining wall in question already exists (unknown build quality of wall but is built on bedrock (test pits have been dug) but part of it makes up the back wall of our porch and we’ve had no issues with damp through the wall, condensation is another matter though!) and is on land owned by us, Who would be the best person to engage first to assess whether extending using the retaining wall is even possible; architect or structural engineer? Again, hope this makes sense and thanks again in advance for any responses!

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5 Answers

jabrickworks

Rating: 5 out of 5
Larne
Retaining walls should be at least 900mm (3 feet) from the main structure to allow sufficient water drainage and passage. Although there is ways of tanking the walls if this can’t be achieved best speak to your architect and they’ll advise with building control.
Answered2 March 2022
6

Yorke Architecture Ltd

Rating: 4.9 out of 5
Doncaster
In theory, yes, if done properly. However, retaining walls are usually owned by the ‘high side’ so you may well be on someone else’s land if this is a boundary.
Answered2 March 2022
2

Anonymous user

Not a good Building practice , and would not be accepted by building control . A strip foundation is needed to be 750 min depth from DPC . And the concrete strip to be 600 mm X 300mm minimum .and could vary around the U.K.👍
Answered9 December 2022
2

Spencer Clayton

No reviews yet

Walsall
Get in touch with building control they will give you the best advice and all building regulations.
Answered2 March 2022
1

Marchbanks Architectural Design

Rating: 4.9 out of 5
Llanfairpwllgwyngyll
There are ways to minimise use of space, that will very much depend on your specific situation. Building tight to an existing retaining wall is always difficult, not least as you need to consider the foundations of the retaining wall and any load imposed on the retaining wall that might impart a turning moment on that foundation. Extra load on what is at the moment the outer edge of the foundation could increase the turning moment, depending on ground beneath. Eg if the foundation loads on solid rock, there may be less problem than if you are on ground that is less stable. We have recently produced a new extension with the new extension cavity wall abutting the new retaining wall. So easier with a new retaining wall. Best bet would be an architect/architectural designer with either an inhouse engineer or a separate engineer - for instance we tend to take designs right through building control to ready for build stage, others may not. My feeling is that if you are on solid bedrock, you will likely be able to build up to the retaining wall, but would necessitate a cavity wall not a cavity and inner skin to ensure suitable waterproofing and meeting of part L regs, you may well be looking at a 125mm cavity, so overall a 325mm wide new wall plus finish thicknesses. You might be looking at tanking solution on the face of the existing retaining wall and bituthene or similar vertical d.p.m bedded tight between the two walls as belt and braces - all depends on the actual situation
Answered5 March 2022
1