So you would like to know how to build a rock retaining wall. Good decision! It’s not as difficult as you might think. I went back and forth between various ideas when I was making my decision. Do I build a wooden sleeper wall, or bricks, or rocks. What will last the longest. I really liked the idea of building a gabion wall, however the caging is quite expensive so I moved away from that idea.
I won’t go into the pricing of all types of walls as common sense says you have done your research and weighed up your options already. You are here because you want to know how to build a rock retaining wall, or you want to find out how hard it is.
I am glad I went with my original idea and built a rock retaining wall as it is strong, looks good and will last forever. Now let me walk you through the process that I followed to build my own rock wall.
Council Regulations – If you want to do it by the book
Get your tape measure out and measure exactly how long and high you will have to build your retaining wall. Remember to check your local council regulations in relation to how high you can build a retaining wall without getting it professionally engineered. This can dramatically increase the cost. Let’s proceed.
What type of rocks am I going to use – What shape
You might be lucky like I was and have all the rocks you need, however if you don’t you will have to do some research and get some prices and get some rocks delivered. If you use the measurements you have taken you should be able to approximately work out what material you will need for the front fascia of your wall and backfilling.
Remember you will need front rocks to make your wall look pretty and plenty of smaller rocks, approximately 5cm diameter to backfill in between.
Foundation, foundation, foundation – Getting it right
Now, every article or instruction I researched and read about building a retaining wall foundation was so confusing and detailed it was like building a foundation for an aircraft hangar. So I decided to go back further, 200 years back in the past and research what the old rock wall builders used to do.
What I found was that the key to the foundation was to make sure that any water that flows above the wall, has to be able to get out. The primary cause for walls to move or bulge out was sediment and lack of water drainage. This will become more relevant below.
Back to the foundation. General rule of thumb is if your wall is 1 metre high, you will need your wall to be 1 metre deep into the ground or bank you are retaining. You can get away with less depth in some cases, but you will want your wall to stay where it is for ever so I believe it is definitely a smart move. If you are shy on space then you might be able to decrease the depth. It all depends on what you are retaining.
So if your wall is going to be 1 metre high, measure out 1 metre from the bank and put a string line or paint mark the entire length of the wall. I prefer to use a string line as you have a physical guide when laying down your foundation rocks.
Level out your foundation area so you have a good flat surface to work with. Make sure the foundation is properly compacted or better still virgin ground that is naturally compacted and not going to be prone to sinking. I wanted my rock wall to look quite rustic so I didn’t concern myself with getting down on the ground using a water level etc etc.
Laying down your foundation rocks – Pretty easy really
This is where you are going to want to lay all of your largest rocks the entire length of the wall. Depending on how many rocks you have, you have the choice laying them flat, or as I have done in my rock wall, I stood all the big rocks up as I liked the look of it. Use your string line for a guide. Make sure they are sitting straight and are well supported from the back and sides and compact with soil around every rock.
Backfilling your foundation rocks – Important for drainage
Now using soil or something that you can compact to the level up to the top of the rocks. You must compact this. Any water falling from above the bank is going to hit this level eventually and must be able to escape from the wall. The aim is not to have any water sitting or pooling in this area as it could lead to your wall moving in the future. I chose this method as it alleviates the need for gravel and sand trenches, not to mention drainage pipe at the back of the wall between the fill and the bank. This is also the method I researched on the net that has been proven to work.
Next layer of rocks – It’s a jigsaw puzzle
It is as easy as laying rocks to fill up the gaps to increase the height as you go up each level. The rule is each new layer of rocks you lay must be at least 1 – 2 inches closer to the back of the wall so you are gradually heading towards the bank. This will give your wall stability and ensure the rocks can’t fall over the front.
An important tip also is if you try to achieve absolute accuracy with rocks and try to make it perfect it will make it very difficult to continue this all the way through your wall build. If you stick to laying the rocks naturally where they fit and not worrying about making it perfect, the job will go much smoother. I’m writing from experience, trust me.
After each new level of front fascia rocks are laid down you have to back fill with smaller 5cm diameter rocks behind to take up all gaps and reinforce the front rocks.
Reaching the height – You are nearly done
When you have done a few layers and you are getting close to your required height, it is a good idea to choose your top rocks carefully so that you arrive with a level final layer, or as much as possible.
My own experience
I have written this article using my own experience as a guide. The entire project went well. I did my research and the time-honoured method worked well. My retaining wall has seen some major rainfall and hasn’t moved.
The pictures are of my own rock wall as well as a smaller garden wall I have built.
As previously mentioned there are a lot of ideas on how to build a rock retaining wall. I’m just keeping it simple. If anyone would like more information or would like me to build one for you please let me know. You can contact me on 0433 567 040.