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Retaining wall close to slab

My house (currently in construction) has a dip in land from front to back. The slab at the front is same height as the curb, and at the back is about 600mm above ground. I want to raise the ground level to match the slab. I have a 4 meters deep backyard.

I was considering DIY'ing a timber retaining wall about 1 meter from the slab on the 3 sides that need it. This leaves me with 3 meters of lowered backyard. I could move it to 1.5 meters by adding in-built sitting at some places within the fence.

This brings me to my question (finally! 😋 ). Is it a vise move to DIY a 500-600 mm high timber retaining wall (200x75 treated pine) about 1 to 1.5 meter away from the house slab? I would appreciate some insights from the experts.

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Comments

MitchellMc

Hi @arian10daddy. many thanks for your question, I'd be happy to kick-off the discussion.

Personally, I'd need a diagram to fully appreciate what you are wanting to achieve with the retaining walls. If you could illustrate a top-down view and a cross-cut view of the property and where you are putting the retaining walls, I'm sure it would assist our members in giving some quality advice. Please bear in mind that if you build a retaining wall close to a boundary, or it affects the adjacent property, then you might require planning permission and engineering. If you are building in close quarters to the house slab considerable thought would need to be put into the drainage solutions and water will need to be directed away from the slab.

We look forward to assisting with your project and any additional details or diagrams will help in that process.

Mitchell

arian10daddy

More details as requested:

Top view -

The outer black line represents an existing fence with neighbours. The inner black line represents the house slab. The red line represents what I am currently thinking of putting the retaining walls. The retaining walls on the sides are a gradual fall from 0 mm (front) to around 500-600 mm (back). The entire back retaining wall will be 500-600 mm tall. Ignore the need for stairs for now just for ease of understanding.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/9143#Comment_9143

Hi @arian10daddy,

Are you intending to fill the area behind the retaining wall up against the boundary fence as shown below, or filling next to the slab to have a 1m space level with it?

I'm struggling to understand what either of those two options achieves apart from creating dual levels in an already small backyard. If dual-levels are your intention and are a design aspect you are going for, then I see no problems if all drainage issues etc are addressed. Once again due to the close proximity to the boundary fences, you might require an engineer to design it.

I assume I am having trouble understanding, as I would presume a better use of the land would be to have the rear portion of the retaining wall against the rear fence, filling the entire area to give you one level 4m space.

Mitchell

arian10daddy

To answer your first question @MitchellMc, I will be filling next to the slab to have a 1m space level with it. My backyard is deeper than the slab.

Although initially wanting a raised and level backyard, one of the reason for not going all the way to the back fence is that the last 2 m of the backyard is an easement. Would the retaining wall be a "permanent structure" that I shouldn't build over an easement.

The other reason for not going all the way back to the fence is the added headache and expense of screening required to increase the fence height.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/9144#Comment_9144

@arian10daddy many thanks for the clarification, as that allows me to understand the project further.

Easements can be a difficult issue and I would advise you contact the relevant authority who governs the easement to get clarification on what you can or can not build on or near it. What the easement is for will ultimately dictate what work you can complete. For example, if the easement is for access to pipe works, then building a retaining wall which restricts access to the area would be a decision which needs careful consideration.

I would be of the opinion that a retaining wall would be considered a permanent structure as any rectification work would be extensive.

Mitchell

arian10daddy

https://www.workshop.bunnings.com.au/discussion/comment/66837#Comment_66837

Thanks for the clarification. The easement of 2 m is basically due to a sewer pipe (i think) at 0.9 m from back fence. I'm considering raising the entire backyard as not a viable option because of all the conditions surrounding it.

That brings me back to my original question. Is it a good idea to DIY a 500-600 mm timber retaining wall 1 m away from the slab without the need of an engineer to design it?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/96212#Comment_96212

@arian10daddy,

There are many different regulations on the height and location before needing a structural engineer in each state. Please verify the height and location regulations in your state by contacting your local council. Once it has been ascertained that a retaining wall is possible in that location, I'm sure our members will be more than happy to assist with your questions.

Mitchell

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