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How to build a retaining wall?

Hello.

I am planning to level the back yard. Please guide and give suggestions where you feel like

Installing 2 layers of 200X50 mm timber sleepers and adjoining them with C and H post ( I will take off the existing post and install 0.9m post so it can accommodate one more sleeper)

Fill the area with garden mix

layout the natural turf

Q 1. Do I have to color the sleeper before installation for longevity?

Q 2 . The total height of the retaining wall is 400mm. Do I need to have drainage?

anything else I have to consider before starting the project?

Access to backyard is narrow and I have to use wheelbarrow to move the soil.

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Comments

MitchellMc

Hi @Mo2,

It sounds like you're on the right track with your plan to level the backyard. One thing to consider is whether the additional sleepers will be enough to achieve a level surface, particularly if there's a significant gradient in your yard. If the slope is steep, you might need more than two layers of sleepers to ensure the area is properly levelled.

The timber sleepers you’re using are likely H4 treated, which makes them resistant to moisture and ground contact, so there’s no need for additional treatment for longevity. However, if you're after a different look or colour, staining or painting the sleepers before installation is a good option. It’s much easier to do this before you fill the area, and it can offer some extra protection if you use a quality outdoor stain.

For drainage, even though your retaining wall will only be 400mm high, it’s important to include proper drainage to prevent water buildup behind the wall. Excess water can create pressure, leading to structural issues over time. Installing a perforated drainage pipe (often referred to as an agi pipe) at the base of the wall, covered with gravel, will help direct water away and reduce the risk of future problems, especially with the garden mix and turf retaining moisture.

You should also make sure to compact the soil well after filling to avoid any settling or uneven patches when you lay the turf. We hire compactors for this. Given that access to your backyard is narrow and you'll need to use a wheelbarrow, it's worth planning the job over a couple of days to avoid exhaustion. Just keep in mind that it may take a bit longer to move the soil, but taking your time will ensure a better result in the end.

Please let me know if you have any questions.

Mitchell

Mo2

https://www.workshop.bunnings.com.au/discussion/comment/42554#Comment_42554

Thanks Mitchell for the quick response, I really appreciate that.

Can you please advise the size of metal post that can be suitable if I am stacking three levels of 200 X 50 mm H4 Treated Pine sleepers? Is 1.2m sufficient? 0.6 m in ground and 0.6 outside.

And, I have storm water pipe in the garden and this area will be filled up with soil for levelling the garden. My question is how can I raise that pipe so it’s opening end is at the ground level?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/83397#Comment_83397

Hi @Mo2,

Typically, your posts should be twice the height of the wall. It's always best to follow the guidance of the post-manufacturer you're using.

You'd need a plumber to extend the pipe's length. It should be a relatively simple job of glueing on a new section of pipe and cap.

Please let me know if you have any questions.

Mitchell

Mo2

https://www.workshop.bunnings.com.au/discussion/comment/106600#Comment_106600

Hi Mitchell

Thanks again for your response.

I have level the ground and it’s just 20mm above if I stack 2 sleepers.

My question is can I use 2 layers of H4 200 x 50 mm and one layer of H3 70 x 45 mm on the top.

I will the fill up the area of post with pebbles so the timber will remain intact in the post.

Thanks in advance

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/120513#Comment_120513

You could do @Mo2, but the 70 x 45mm timber is only H3 treated, so it's only suitable for above-ground use and not for contact with soil. It will deteriorate fairly quickly if soil is placed against it. You might need to cut down some sleepers to finish off the height to the correct level.

Mitchell

Mo2

https://www.workshop.bunnings.com.au/discussion/comment/129084#Comment_129084

Thanks Mitchell again for the response.

Do you recommend cutting the timer sleeper in between to reduce the length and add few more H post in between for better grip strength OR

Should I use few metal pegs behind the wall to maintain the resistance against soil?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/134526#Comment_134526

I'm sorry @Mo2. I'm not sure if I quite understand what you are proposing there. Could you draw a quick sketch to illustrate?

Mitchell

Mo2

Yeah no problem.

the sleepers I am using are 5.4m in length. To avoid the bend once I fill the dig with soil, I am thinking to cut the sleepers in 2 or 3 pieces and connect them with H post so they don’t bend.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/43029#Comment_43029

Great decision, @Mo2. 5.4m is far too long to use in a single span. Typically, you wouldn't want to go over 1800mm for 50mm thick sleepers. Cutting them up and adding additional H posts is a wise choice.

Mitchell

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