What timber to use for retaining wall?

[ososbg]

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

[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]

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]

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]

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

[ososbg]

@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]

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]

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]

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