What timber to use for retaining wall?

Hi all,

First time poster here and sorry if it's a naive question.

I want to build a retaining wall and also to be a raised garden bed at the same time. I've two sides in my backyard I want to use both of them, one side is 15m and the other side is 14m, the retaining wall height is about 500-600mm.

My question is, what timber I should be using for this:

1.8m H4 Treated Pine Sleeper 200 x 75mm.

2.4m H4 Treated Pine Sleeper 200 x 75mm

1.8m H4 Treated Pine Sleeper 200 x 50mm

2.4m H4 Treated Pine Sleeper 200 x 50mm

Thanks in advance

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Comments

Jewelleryrescue

Hi @ososbg

All timbers you meantioned are winners But read more to see some pros and cons.

Normally you choose the long 2,4 lengths as that means digging less post holes. But if you want a stronger wall choose 1.8meter lenghts as you will have shorter spans between posts and more support. 75mm thick will last longer and be more stronger than 50mm. Typically people use 2.4 x 50 as a retaining wall as a guide. A 1.8 x 75mm timber wall will be the strongest treated pine wall and will last the longest 25 plus years.

14 meters 2.4 = 5 lenghts with a remainder of 0.83 of a timber Iength ie cut it to size.

15 meters 2.4 = 6.25 lengths 6 whole and a quarter length.

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/33712#Comment_33712

Hi @Jewelleryrescue , Thanks so much for the detailed response, any idea about the durability and lifetime of the 50mm timber in terms of how long it can last for, I'm based in Melbourne so lots of rain and changing weather, and also, what's the recommended spans between each post in the case of both 75mm and 50mm 1.8m timber.

Jewelleryrescue

https://www.workshop.bunnings.com.au/discussion/comment/79178#Comment_79178

Hi @ososbg

50 mm about 20 years but naterally many factors may alter that life span. I got 22 years out of 50mm at sydney. Melboune maybe damper and wetter it was at templstoe where my grandfather lived.

14 Meter 1.8 timber 7 full lengths and 0.78 remainder off cut = 1.4 meter long as an estimate.

15 Meter 1.8 timber 8 full lengths and 1/3 remainder 600mm estimate.

Start at one end of retaining wall with a starting post and start laying out rails end to end touching will quickly give you post hole locations along a string line. If you hit a big rock digging alone post holes simply shorten that section so your post goes into clean earth and continue from there .

Dave-1

Afternoon @ososbg

First up I would like to say howdy and welcome to the Bunnings community page 🙂 A good place for exactly these type of questions!

I have a preference to a gabion style retaining wall which I will add a link afterwards 🙂

You are asking about timber, I like the shortter distance between the posts and also the 50mm thickness mainly because its only holding back 500mm-600mm of soil. The depth of the hole is always something to make sure you do right. The deeper it is the less it will want to bow out over the years.

For the post hole I would suggest at least 600mm deep, preferably 800mm deep or even 1m if you get a post digger.

The stronger the posts the longer it will last without that lean to it we know so well.

Now if you want a retaining wall that will not lean.... Then Gabion walls 🙂 Steel mesh basket with rocks inside, configured how ever you like, dosnt require a foundation other then packed earth. and lets water drain through. The disadvantage is the space it takes up. for a 600mm high retaining wall then id be making it 400mm wide. Here is one of my projects with gabion walls, there are a bunch of different ones if you check out my bookmarks 🙂 Large Gabion Wall Build Its a true retainng wall and about the size you are asking for. Not that Im trying to convince you to go away from timber retaining walls 🙂

Dave

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/103910#Comment_103910

Thanks so much @Jewelleryrescue , I'll check this out, much appreciated.

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/33742#Comment_33742

@Dave-1, thanks for the warm welcome and for the great suggestion, first time to hear about the Gabion retaining wall, will have a look. Any idea about the cost compared with timber, from the looks of it, it cheaper but any comment from you would be appreciated.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/79187#Comment_79187

Welcome to the Bunnings Workshop community @ososbg. It's wonderful to have you join us, and many thanks for your question about selecting timber for retaining walls.

I thought you might like to check out a couple of helpful step-by-step articles: How to build a retaining wall and How to build a raised garden bed. I'm sure they'll give you a good idea of how to go about the construction. I'd also recommend you check on local regulations for the maximum height of your retaining wall before it needs engineering.

Please let us know if you have any questions.

Mitchell

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/79187#Comment_79187

Afternoon @ososbg

Cost... A couple ways to go about it.

Straight out basket

Jack 80 x 40 x 40cm Rectangle Landscaper's Plant Support Garden Gabion * one = $57.11ea

15m run 19 baskets at 400mm high, or 38 baskets at 800mm high.

You could go for the smaller sized baskets as a second course but not sure how it would look?

Jack 650 x 300 x 150mm Black Rectangular Gabion * one = $36.69ea

For Filling these baskets I used broken up concrete pathway. I also used a whole bunch of rubble/stone that I broke up and "hid" in the middle of the baskets so the facing side looked nice.

Now you could go down the track of buying larger pieces of mesh (Approx $170ea for a 2.4m by 1.8m gal 50mm square panel ) and making the baskets yourself. I did that and made three large baskets, saved a lot of money that way and time. If you check out the projects I explain how to make the baskets. They are easy as.

Dave

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/103937#Comment_103937

This is fantastic, @Dave-1 , thanks so much for the detailed response. I'll definitely investigate this option.

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/103935#Comment_103935

Hi @MitchellMc , thanks for the warm welcome and the links, the video is very informative, thanks for sharing, I've got a few questions for you:

1- What's the drill and the drill bits used, I would appreciate if you can recommend something for me for DIY. I've got big rocks in my backyard and looking for something that can help drill through these rocks.

2- What's the diameter for the holes for the posts for the 50mm timber sleepers.

3- What posts do you recommend for me based on the measurements I've in my main post, shall I go with the timber posts as in the video or with the steel ones ?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/103937#Comment_103937

Hi @ososbg,

For the construction of the retaining wall and screwing the horizontal sleepers to the posts, you'd only require a drill driver and landscape screws. The screw box should include the star drive bit needed. For drilling into rock, you'd require a hammer drill (preferably a mains-powered version) and masonry bits.

The rough rule of thumb for retaining wall posts is half in the ground, half out of the ground. For a 200mm sleeper, you'd need around a 400mm diametre hole.

The choice is yours on whether you'd like to go with steel or timber. The steel does have the advantage that no drilling is required as the sleeper slips into the post. Here's a great guide: How to build a raised garden bed for privacy.

Please let me know if you have questions.

Mitchell

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/119020#Comment_119020

Thanks so much @MitchellMc , too much to digest in the weekend, will spend sometime today to learn and will circle back for any questions. Thanks again.

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/128032#Comment_128032

Hi @MitchellMc , this is me again 🙂

I've progressed my project but I did 2 big mistakes and I need some guidance from you:

I bought the 75mm timber sleepers, but unfortunately I didn't pay attention and I got CCA instead of ACQ or MicroPro treated timber and I finished half of the job now. 😑
I used the timber posts inwards instead of doing it outwards, so, the load now will be on the nails instead of the post if I understand this correctly (as in the attached photo).

I did some research and found out the risk of using CCA can be mitigated if I use builder's sheet or plastic sheet before I put the soil, any guidance on if this is a good idea or there's a better option, bonus point if you can post links for some products you can recommend (sheets or anything else).

Also, will the posts position will be able to handle the load from the soil, the max height I had for the retaining wall is 60cm.

Thanks in advance.

Jason

https://www.workshop.bunnings.com.au/discussion/comment/133951#Comment_133951

Hi @ososbg,

Just a heads-up that @MitchellMc won't be back on the site until tomorrow. Let me see if @EricL can assist in the meantime.

Jason

robchin

Hi @ososbg

Good luck with this project. Sure it will turn out great.

I work in the Risk and Compliance team at Bunnings and wanted to make a note about using treated pine. May not be relevant to this example but I would put out a general warning if you are building raised garden beds for vegetables and herbs then be careful with your timber selection and don't use timber treated with copper chrome arsenate (CCA) - they're the ones that look a little green. There are alternatively treated timber sleepers available.

Just a general word of caution.

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/34460#Comment_34460

Hi @robchin Thank you for the note, as I mentioned it was me being naive and not paying a lot of attention, and hence I got the CCA and already done most of the job, so I don't think there's a way to rollback, all what i'm asking now is how to help reduce the risk of CCA, I did some research and I learnt that I can use a builder's sheet (i don't know what this is) between the timber and the soil, or alternatively to stain the timber with water based stain, again this is my very first experiment so I'm not an expert at all. Hence i'm looking for some guidance if you or someone from the team can provide some help with links to some of your products, that would be appreciated.

EricL

https://www.workshop.bunnings.com.au/discussion/comment/79536#Comment_79536

Hello @ososbg

Can you please tell me what screws you used to anchor the sleepers to the post? Although the raised garden is not too high its always best to have full support when you start filling it. What post size did you use? It's difficult to tell from the photo, is it 90x90 posts?

Allow me to double check the plastic to be used for the garden bed. As soon as I have more information, I'll get back to you.

Thank you for your patience.

Eric

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/104158#Comment_104158

Hi @EricL , thank you for your reply.

I've used 125mm timber construction screws, and the posts are 90x90, the sleepers are 75mm.

Let me know if you need more information from me.

Thanks

EricL

https://www.workshop.bunnings.com.au/discussion/comment/119144#Comment_119144

Hello @ososbg

Thanks for sharing those extra details of your build. Because you've placed your posts on the inside, I would like to suggest using Buildex 16-8 x 125mm Climacoat Type 17 Timber Construction Screw, it's thickness and head size will be able to hold a fair bit of weight.

In regards to the plastic cover, I've conferred with Mitchell and I propose using Builder's Plastic 200um in thickness. My best advice is to make sure to provide adequate overhang at the top and bottom of the sleeper wall.

If you need further assistance, please let us know.

Eric

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/128118#Comment_128118

Hi @EricL , thanks so much for your reply. Can you please explain to me what does um means in the plastic sheets ? and also, how to fix the sheet to the wall, shall I use stapler gun or normal nails. Sorry for asking so many questions and I appreciate your help and the rest of the team.

EricL

https://www.workshop.bunnings.com.au/discussion/comment/133956#Comment_133956

Hello @ososbg

The term 200um refers to the thickness of the plastic 200 microns. The higher the number the thicker the plastic.

In regards to fixing the plastic to the sleeper, it's best to use a staple gun so that it will not create a big hole in the plastic. I also suggest covering the staples with clear sticky tape. But once the soil gets put in it will hold the plastic in place.

If you need further assistance, please let us know.

Eric

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/137601#Comment_137601

Thanks @EricL , this is super helpful.

Mits

Hi, @MitchellMc @EricL could I please check with the experts which type of timber to use for a retaining wall system with seating at the top that would give a similar look to the one in this photo? Also, should it be oiled or varnished? If so, what type? I plan to use this timber for my vegetable garden bed, so I’m looking for non-CCA treated pine options. However, Bunnings currently has very limited supply. The same goes for Sienna MicroPro. Are there any other suggestions on where I might source these material

Thank you so much.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/44887#Comment_44887

Hi @Mits,

The Sienna MicroPro or hardwood would be the best choice for a veggie patch, especially one that doubles as a seat. Due to the different suppliers depending on the area, it would be best to speak with a Special Orders team member at your local store. They'll be familiar with the timber suppliers in your area and can then check all available sources to see if there are non-CCA-treated sleepers available to order.

Treated sleepers typically do not need any protection, but you could stain or oil them if you wished to change the colour or add additional protection.

If you can let me know your location I'd be happy to contact your local store for you to find out what's available.

Please let me know if you have any questions.

Mitchell

Mits

https://www.workshop.bunnings.com.au/discussion/comment/84562#Comment_84562

Thank you @MitchellMc

Can I please ask what do you mean by having double timber for seat?

Also, looking at the picture, can you suggest if it is timber oil or color?

I am based at The Ponds, 2769, NSW. Can you please help me look for the said timber?

Thank you,

Mits.

EricL

https://www.workshop.bunnings.com.au/discussion/comment/107317#Comment_107317

Hello @Mits

It's possible that Mitchell was referring to the sleepers being put together side by side to serve as the seat. Let me tag @MitchellMc to make them aware of your response and to confirm the sleeper configuration. Please allow us some time to check the stock levels at the surrounding Bunnings store in the area.

If you need further assistance, please let us know.

Eric

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/107317#Comment_107317

Hi @Mits,

I'm so sorry for the delay in our reply.

The reference was to a retaining wall that is also a seat, not a suggestion to double the timber for the seat.

At Bunnings Rouse Hill they have ACQ-treated sleepers, which are safe to use as your retaining wall and seat.

The colour of these ACQ-treated sleepers is very similar to your inspiration image, so no additional staining is required, but you could oil them with a natural oil if you like.

Mitchell

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