Has anyone built on top of an existing retaining wall?

Out block is in a new estate and our neighbours block is a metre higher than ours and there is a limestone retaining wall which sits on their side but on the boundary.
We have found out that they have had plans approved to build their garage wall which is 9 metres long, on the boundary line which means this is being built on the retaining wall.

Council will only tell us that it applies with r codes but we have concerns about the extra load the retaining wall will be taking. I have driven around everywhere looking for a similar set up and haven’t found one and haven’t found much online about this set up.

Their builders engineer has stated the retaining wall is sufficient but it seems a bit strange that they can just build a brick wall on top as it is. There is an expansion join in the retaining wall right under where the wall will be.

Has anyone done this before? And have photos or information on how it’s done. While the thought of a 4 metre high wall on our boundary isn’t appealing, I’m more concerned about the bedrooms we will have next to it and how safe that wall will be long term.

usually "on the boundary line" means 200mm off it. the gutter ends up being on the boundary line. they also need to pour a slab somehow (or drive stumps in) so i doubt that the house wall will sit on top of retaining wall.

In this case the edge of the retaining wall is on the boundary and yep, council have confirmed there will be a parapet wall on the retaining wall.

How high is the wall? If the wall had to have engineering certification, you should speak to the engineer.

The retaining wall already there is 1.1metres high. I assume it was engineered as part of the subdivision but the builders engineer has come back as saying it’s adequate to be built on. That is the only information I’m being given.

1,1 m high definitely needed to be engineered. You should follow up the engineer's advice by repeating the advice in writing and asking for his written confirmation of same.

They should have consulted with you first
and have a read of Clause 5.3.8 retaining walls
State_Planning_Policy_3-1-Residential_Design_Codes-for-mobile
Regarding the Wall Engineering get a copy from the council of the engineering details and put up a photo
Cheers
Chris

do you by any chance have a picture of the wall? i'm really struggling to imagine how does one build a house on top of any retaining wall...

Yes we are not sure why we haven’t been consulted with this.

This is the only details the council will send me. The “note” regarding the existing retaining wall is all council are going by in regards to the fact the wall will be adequate. I have argued that the wall was engineered to hold back the soil but not engineered to hold the load of a wall and roof load and that’s where our concern is.

I’m also not sure what the number I’ve circled in red is as that’s our side of the wall but it’s certainly not our ground level?

Actually If those numbers are levels, they are all wrong.

https://1drv.ms/u/s!AgN55OcoLy4TjzxvEma9E62XQXFa

I doubt that's what you have engineered from the land developer on the neighbours side
It would pay for you to dig a small hole and check it, but I may stand corrected
Cheers
Chris

Thanks, if it is in fact what is there, would you say that would suffice to hold a wall and roof load as well?

Council have basically wiped their hands of it and won’t help me further. They have said the retaining certification is for the retaining wall only but because a structural engineer has assessed the drawings, they believe it’s adequate and therefore it is certified.

I don’t believe they have actually been out to look at the wall as they are in the city and we are in the country and are just going on the drawings. The levels they have are all incorrect. There is an expansion joint in the retaining wall where they will be building on top of and I’m wondering if that may cause a problem. Have attached pic.

Not sure whether we just let it go or get another opinion from another structural engineer.

Thanks

Hi Rizzo
I'm not an engineer but I can tell you that for many decades houses in Perth were built on limestone blocks that were simply laid on sand. There would be many thousands of houses still standing built on much less than the retaining wall in question.
If the builders engineers have signed off on it then it really has nothing to do with you and realistically there is little you can do. The full responsibility is on them.
I think you are being a little overly concerned about it. The wall isn't just going to suddenly collapse onto your house. Even if there was movement at some stage it would become quite evident before it becomes dangerous.

[quote="chippy":26nlk27j]Hi Rizzo
I'm not an engineer but I can tell you that for many decades houses in Perth were built on limestone blocks that were simply laid on sand. There would be many thousands of houses still standing built on much less than the retaining wall in question.
If the builders engineers have signed off on it then it really has nothing to do with you and realistically there is little you can do. The full responsibility is on them.
I think you are being a little overly concerned about it. The wall isn't just going to suddenly collapse onto your house. Even if there was movement at some stage it would become quite evident before it becomes dangerous.[/quote:26nlk27j]

Thanks chippy. I didn’t realise this is a common thing, I haven’t seen any built like this on this size of a wall. Our builder also didn’t seem to think it was right which is why we got concerned.

I do realise it’s not going to just fall, but should there be any movement down the track and it needs fixing, it won’t be possible to do it from our side with that wall on top, not without damage to our property.