Leveling backyard

[ximian]

Hi,

This site is brilliant. It's been great reading about other people's experiences on projects I'm looking at tackling.

My post is to hopefully get some advice on leveling my backyard.

My backyard is on a slope where the property line between my lot and the back neighbor is significantly higher than the house.

There's currently a retaining wall in the middle of the backyard (900mm high). Based on how soggy the dirt is at the bottom of the retaining wall (on the lower tier), I'm not sure there's a very good (or any) drainage behind the retaining wall.

Ultimately, I'd like to flatten the entire yard from point A at the highest point in the below diagram to all be completely flat at point B. (I did not include the width of the backyard... I'd need to check but I think it's about 10m.)

• Is DIY-ing this completely out of the question? Or is the scale of this job such that it should be done professionally? I'm happy to chip away at it over a few months if it can be done in phases.
• If possible to DIY, where do I even begin?
• I accept that the retaining wall at the far end would be quite high at >1.3m. Aesthetically, I think it can be made to look good but practically, will this be a usable, pleasant space given that the neighbours will literally be looking down on anyone in the backyard?
• Given the height of the retaining wall, my understanding is that it needs to be approved by an engineer and/or council. Is this correct? Is it possible to maybe tier the retaining wall into steps (or some other restructuring) to not require external approval? (Not trying to do anything dodgy, just want to understand what factors make this job complicated.)
• If I were to do this in phases (ie dig a portion of the yard at a time), where would I even put the dirt?
• Access might be an issue (either from my yard or the adjacent neighbors) if I were to hire a Bobcat and driver to get it done in one go.
• If I were to get this done professionally, what would be the ballpark cost of such a project?

[MitchellMc]

Welcome to the Bunnings Workshop community @ximian. It's fantastic to have you join us and many thanks for your questions.

It depends on your location as to the height in which engineers services are required.

You might like to start by reading this article How to build a retaining wall by @Adam_W. Some other discussions you could find of assistance are How to build a timber retaining wall, Retaining wall in progress, Retaining walls whats the most cost-effective method and Replacing or Building a Post amp Rail Retaining wall.

My thoughts on the project are that you could D.I.Y. it. However, that is an immense amount of material to remove, a significant amount of material will be retained at the property line, engineering is most likely required and stepping the walls down will encroach back into the yard.

I would start by having some landscapers come in and quote the job for you. They'll be able to tell you if they can get equipment in and the cost will likely help you decide on which route to follow.

Let me mention @Yanick to see if he would like to join the discussion.

Mitchell

[Yanick]

Hi @ximian,

Sounds like a big project but would look nice. Being able to do it yourself will depend on your previous experience and if you have at least another person to help you, as several stages require more hands. I would start off by looking at the following video and the rest of Scott’s videos on building a retaining wall. Keep in mind it is New Zealand bases so some regulations will differ, however it is very informative, and will help you gauge if you feel you are up for the challenge.

https://youtu.be/N7N_mknuHHY

There are a lot of considerations with a project like this (underground pipes, drainage, council regulations etc) so I would recommend getting a builder in to give you a quote and further opinion on this project, as @MitchellMc suggested. I would also recommend contacting your local council to find out the regulations/permits that will apply to you.

As far as costs, I haven’t done any quoting before and it is difficult to ballpark without standing on your site. 

Thanks,

Yanick

[MitchellMc]

@Yanick,

Many thanks for contributing your expert knowledge and I trust @ximian will appreciate your input.

Mitchell

[ximian]

Thanks for the response. I spoke with someone today and they were able to come and have a look the same day as they had an opening. They're getting me a more detailed quote but it's in the tens of thousands... between 20 to 40k! Looks like a much more massive task than I anticipated. I'll be doing my due diligence and getting at least one more quote. For that kind of money, I'd definitely be keen to do some of it myself to save costs.

[Adam_W]

Hi @ximian @ welcome!
Okay. That's a big project that will require engineering and council approval if you are to go to full height. Most walls above about 500mm need approval as does retaining near a boundary.
I'm just a but confused though... so you want to remove the existing wall, add a taller wall on the boundary or series of stepped walls?
Rough estimate... you'll be dealing with around 27cubic metres of soil (that's a few big trucks full...) with a weight of around 40 tonnes...
That's a lot of shovel work...
I would suggest that you get some suggestions and quotes from a couple of landscapers and look at the options.

It's not beyond the realms of DIY but I reckon one way or another it will need council approval and likely professionally drawn plans.
If you go for a tall wall that will need engineering drawings and approval, likewise if it's on the boundary. A lot of councils also have restrictions on how much fill you can move without approval.

Worth understanding too that if you home was part of the same development as your neighbours your wall may actually be an engineered element that contains the fill of their backyard or even contributes to supporting their house...

[Jason]

Fantastic advice as always @Adam_W, many thanks for sharing your knowledge and experience. 

Great to read that you're finding the site useful for your projects @ximian. Please don't hesitate to reach out if you ever need a hand getting the most from Workshop or have any feedback about how we could make it even more helpful to you. 

Jason

[ximian]

Thanks, @Adam_W ! Yes, I wish to remove the existing wall in the middle and add a taller wall along the boundary.

And yes, I agree on getting more quotes. The one quote of 20 to 40k of just the earthworks is a big item. But I'm really keen to get it done. Won't have that kind of funds for a while so figuring out how I could do it in a phased way.

I'll get another quote.

[Adam_W]

No worries at all @ximian 
20 to 40K sounds a bit steep but always hard to say without knowing the variables like site access, soil type etc.
My biggest concern, and this relates to soil type & what the original purpose of that existing wall is, would be how you keep the boundary shored-up as the project progresses.
1.3m +/- is pretty tall and cannot be left unrestrained for anything but a short time.  The fill would need to be removed and cut with a batter (angle) to prevent slippage and then would have to be backfilled.
The whole project will need engineering done especially when it comes to getting the drainage right.
Another thing to think about too is what is underground?
If you hit rock then you'll be up for some serious demo costs or will have to totally amend plans. If it's clay you will have an area that may well have drainage issues.
Simple fact is it's a large project. Don't rush it, get multiple quotes because often that's where you'll have some different ideas added to the mix and... make sure you keep us up-to-date with what's happening or ask us any questions!