How to build a low retaining wall?

@EricL you have made so many helpful posts on related threads so tagging you in case you can help with this too.

https://www.workshop.bunnings.com.au/discussion/comment/38095#Comment_38095

Hello @matt234

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thank you for sharing your question about a raised garden bed.

I suggest having a quick look at this discussion - How to lay bricks for raised flower bed? by @Brunnie_Rich. Some elements of your questions are discussed in the post.

In regards to the trench level, I suggest having the soil level all the way around. In this manner you won't have to compensate by building a concrete base that is higher on one side. I don't recommend attaching anything to your house foundation. It's best left alone so that your raised garden bed will be independent of the house foundation.

You can pretty much use any brick you prefer; The advantage of the hollow brick of course is that you can insert Reo bars for extra support. This will require precise brick laying on your part, if you decide to reinforce the wall. The holes in the brick must line up in order for the Rio to pass through.

I definitely suggest putting road base to provide a stable foundation. You'll see this discussed in the post I suggested. Putting Reo mesh into the footer is necessary as it will add strength and keep the footer stable should any breaks occur.

When you begin putting the bricks in, I suggest filling the gap at the back between your house and the garden bed when it reaches the original soil level. In reference to this, I also suggest a minimum gap of at least 100mm between your house wall and the brick garden bed. The gap between the garden bed and your wall will facilitate air flow and prevent condensation from forming.

Filling the gap between your garden bed and the house should not be an issue, ordinary soil will suffice. But I suggest tamping it to make sure that it does not settle unevenly. As to your final question, I suggest building away from the existing brick wall by at least 100mm. As I mentioned earlier, it's best not to attach anything to your house foundation and leave your raised garden bed independent.

Here are some handy guides once you've built your raised garden bed:

Let me call on our experienced members @Dave-1, @homeinmelbourne and @Brunnie_Rich for their recommendations.

If you have any other questions we can help with, please let us know.

Eric

Afternoon @matt234

Nice excavation I muist say 🙂 It gives you a decent area to build easily. I havnt done any brickwork before tho gabion retaining walls yes I have.

With your brick wall I like the tamped roadbase (not worried about sand being under it) then concrete footing with reo as its a sizeable length.

I do have a question, where will the water go? Its pretty much like a dam that you are building and to me that means the water will change its course and pool elsewhere. The Fence post I can see is something I would factor in. One day you may want to replace it and if I have read right then the retaining wall is right next to the post. I do like the 100mm from the house (tho would like a larger distance) , especially to allow the timber to breath, tho as the fence post issue you will be blocking out the lower weatherboard courses from being repaired/painted type deal.

From what I can see the wall is going to be around 5 brick courses above the under house ground level? I wonder if it would be better to leave around a foot gap for maintenece issues between the house wall and new retaining wall? If its all goingto be back filled id go bessa blocks as less bricks to lay.

Last question, does the ground slope towards the house or away? If its towards the house and in particular that excavation point I would suggest to factor in drainage..

I had a water issue with araised garden area as well. In the end I excavated it all out and installed a gabion wall around 800mm from the brick wall.

Gabion Wall to stop water ingress to garage is the project if you want to have a wander through it.

I was going to do exactly what you are suggesting at first. The more I thought about it the more I did not want to have to dig up, pull up stuff to fix anything if it became an issue down the track. I decided to instead make the distance wider and use it functionally. One day I will have a door at the end and a workshop under the house. Thats the plan.

Dave

https://www.workshop.bunnings.com.au/discussion/comment/38106#Comment_38106

Hi @matt234

Those were excellent points raised by @Dave-1. I agree with him in regards with looking after water flow and drainage. It's important that your raised garden not block the natural flow of water as it might flood the bottom of your house.

If you need further assistance, please let us know.

Eric

Thank you both, @EricL and @Dave-1.

The question I had about the level was a bit unclear. The base of the trench is a flat single level, my concern is that this base is lower than the concrete footings I've unearthed at either end and at least partially the corner house stump. I wasn't sure if that would create issues with any of those cracking and falling away towards my trench.

The minimum I was going for between the wall and the house was going to be 100mm, but on reflection that'll make it hard to do painting etc as Dave mentioned so I might see how far out I can get it without leaving myself a tiny unusable garden bed space. (the dimensions I gave are just for the solid concrete footing, currently from there to the edge of the bed would be ~500-600mm so could probably bring it back a bit.) Will have to think about that fence post... not sure how much I can do about getting close to that.

As for the gap of 100mm between the wall and the patio wall on the right side, if I leave that gap what can I do to stop the soil etc eroding through that gap around the wall? Presumably I'll also need to just bury up to covering that footing again. I could take a few more measurements and see if I can do my footing at the same level, and then hand tamp some road base between the footings? I know I should leave 100mm between the footing edge and the side of the wall, is it the same at the end of the wall? The patio clearly hasn't done that, its maybe 20-30mm. Just thinking I could end up with quite a gap if its patio brick wall, ~30mm footer overhang, 100mm gap, 100mm footing edge space (labelled in red in the image). That's a lot of space with nothing holding back the garden bed. (if not clear, I'm just building an L shaped back wall to an existing bed that previously had no back wall and just filled from the patio to the housewall to the fence) I've uploaded a sketch (not as nice as a CAD) top down view in case it helps a bit.

Regarding drainage, the block slopes towards the right of the first image, so I'm not too worried about it pooling as water has never pooled in that garden bed before so I assume it drains out through the sandy soil pretty freely.

As for the brick type, I was looking at the versawall or something similar for 'locking' so I don't have to mortar them in, vs besser blocks which I would. It does feel like it would be a lot easier than all that brick work. Might do the footing then see how handy I'm still feeling.

Lastly, on the footing, I read somewhere that it should be 500mm wide, though can't recall where... What do you suggest as trench mesh for a 500mm wide footing? Looks like the options to buy are either 600mm wide, is it enough if I cut something like this in half and its about 300mm wide but with an 'open' end so functionally probably more like 250mm? https://www.bunnings.com.au/jack-600mm-x-5m-reinforcing-mesh-roll_p1060319

https://www.workshop.bunnings.com.au/discussion/comment/38115#Comment_38115

Evening @matt234

Ok, I think I have it now. You can run the retaining wall right up to the patio brick wall. (no worrying about the red distances) as to the double brick wall with the versawall, How high are you making it?

I went straight to the idea of a gabion cage with a earth filter on the inside to stop the fines enetering that cage. Free drainage as well as keeping the soil off your wall. The smaller cages Bunnings sells in a few different sizes. Incredibly easy to use and no foundation needed. (check out my bookmarks) gabion basket shows a bunch of different sizes. Definently would work well for retaining wall away from the edge of your place. Best part if you ever change your mind, need to work on them then its easy enough to remove them 🙂 It would bypass a bunch of concreteing and brickwork.

Dave

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/38115#Comment_38115

Hi @matt234,

I just wanted to add a few of my thoughts to the conversation.

I'd suggest you set the height of your footing based on the level of the highest existing concrete. This will mean everything can be backfilled so there'll be no stepping and there'll be no worries with the existing footings being exposed and cracking or breaking away.

With the trench mesh, it should extend to the full width of the footing. The edges of the concrete are the most likely place for fracturing, so it's best that the reinforcing extends as far as possible without poking out the side. This will help distribute any load applied to the edge of the footing through the full extent of the footing.

There is no issue with cutting the trench mesh to the exact size required. Having an "open" end is no issue as it will be held in place by the concrete once poured.

@EricL will be back online shortly to add his thoughts, but in the meantime let me know if you have any other questions I can assist with.

Jacob

https://www.workshop.bunnings.com.au/discussion/comment/81257#Comment_81257

Hi @Dave-1

Can I trouble you for a pen and paper diagram on where you would locate the gabion cage on the garden layout? I think it's a n excellent solution and would definitely hold the soil in place.

Thanks!

Eric

https://www.workshop.bunnings.com.au/discussion/comment/38115#Comment_38115

Hello @matt234

Thanks for the additional information about your retaining wall project. I've had another look at the photo you posted and just realized that your garden is much higher than the weatherboard of the house. Please let me know if I'm looking at this incorrectly. Does that mean that when you push the soil back it will be at the level of your grey fence?

If that's the case, the concrete base will need to be high. Have you considered having the base installed a little higher? This will help with not having to build such a tall base footing for the retaining wall. Let me re-draw the layout so that you'll get a better idea of what I'm proposing. As soon as I'm finished, I'll post it here.

Eric

https://www.workshop.bunnings.com.au/discussion/comment/38115#Comment_38115

Hello @matt234

I've re-assessed my proposed solution and would like to amend some of the ideas I suggested. instead of having a gap near your brick area, I recommend building right up to it, but not anchoring to the brick wall. This goes for the other side of your retaining wall. It's main purpose now is to prevent soil from going past the retaining wall.

I suggest doing some preliminary measurements, how tall will the concrete base be? how many levels of Versawall blocks will you be putting in? This should give you a better idea of the layout and quantify the products you'll be using.

For example, if the concrete base is 100mm and each Versawall block is 200mm tall you would have a total height of 500mm if you were to put two levels of the Versawall. You'll now have o determine where will the soil end up once you have part of the retaining wall up and installed.

I've drawn up some sample sketches and placed them below, please let me know if you have any questions regarding the placement of the Versawall blocks. The gap I provided for this drawing is 200mm and your concrete base is 500mm wide. These are just suggestions, and you can change their layout to suit your plans.

Eric

https://www.workshop.bunnings.com.au/discussion/comment/105337#Comment_105337

Evening @EricL and @matt234

Here are a couple of sketches of a gabion styled retaining wall. Much like the one I posted earlier Fixing water ingress issues in garage but shorter and made with off the shelf baskets (tho you can make your own cages a lot cheaper if you wish)

01 04-06-2024.jpg

This is how you have it now, you have done all the hard work! I suggest at least 50mm roadbase type gravel that is tamped down. If it levels out with the top of your foundation concrete all the better. But it will need to be compacted a bit. (I am presuming that that dotted line on your drawing is a garden edge 🙂 )

02 04-06-2024.jpg

I messed up sketching (couldnt find a pencil lol so used pen.) So new pic

So I am taking a guess and saying your retaining wall is 800mm high If its shorter then that can be accomodated as there are a few different sized baskets available off the shelf.

Jack 80 x 40 x 40cm Rectangle Landscaper's Plant Support Garden Gabion need 9 at $58.00ish ea

Jack 65 x 30 x 15cm Landscaper's Plant Support Garden Gabion $36.00ish if you are going for a retaining wall 650mm high (400mm plus 150mm baskets)

Jack 40 x 40 x 40cm Landscaper's Plant Support Garden Gabion Cube $32.00ish ea is a square corner cube if you are only having a retaing wall at 400mm high.

The lower section of the drawing is a side view of what you may see down at ground level. Most of the baskets will be below ground depending on what type and height you go for. I would suggest to make it easy for you that you keep that 400mm air gap between the wall of the house and the edge of the gabion wall. On my gabion projects I show how you can join them together if you want that. The cages would allow water to travel through, hold back the soil with a geotex cloth and last, well last for a long time 🙂

If you want more info on how to for the gabion wall just let me know. I am a fan of them 🙂

Dave

https://www.workshop.bunnings.com.au/discussion/comment/119803#Comment_119803

Hi @Dave-1

Thank you very much for doing that diagram, I'm sure @matt234 will find it very useful.

Eric

https://www.workshop.bunnings.com.au/discussion/comment/81262#Comment_81262

Oh thanks @JacobZ , I read somewhere that the reinforcing should always be at least 50mm from the edge so was factoring that in.

https://www.workshop.bunnings.com.au/discussion/comment/105339#Comment_105339

Thanks @Dave-1 and @EricL , super helpful! My wife wants the brick top so I think the Gabion might be out even though it certainly is much easier! Though this makes me think I might be wise to do the locking blocks and then just rest bricks on top for now, once happy its all stable etc I can mortar the bricks in place.

Yes @EricL, the garden bed is higher than the wall. Where you see it at the top of the trench under the grey fence is its natural level. So I would have 1 brick course higher than that so the top of the wall aligns with the bottom of the fence. The yellow string line is the wall level - from just above the patio render, to just above the plinth boards, to the base of the fence.

The trench is currently 750mm deep to build a 350-400mm wall. I was thinking 2 courses of versawall/locking bessa blocks (only 1 leaf/skin thick though not double like the revised CAD image) + red brick toppers, or 6 courses of double brick (double because people said single wasn't strong enough to retain (though 350mm isn't that tall...). This is because the wall needs to be 350mm above the underhouse 'ground' level to match the garden bed edge, then 70mm for 1st brick course buried, 150mm for the slab (perhaps overkill), 100mm for roadbase, and trying to get under the roots etc took it another ~80mm further which I plan to put back in as soil and compact before adding the road base.

Another rough drawing attached of the side view.

https://www.workshop.bunnings.com.au/discussion/comment/119805#Comment_119805

Morning @matt234

🙂 Thats ok, ideas are just that, ideas 🙂 They dont cost anything to consider.

Think your sketch looks good, cant see any issue with it.

Dave

https://www.workshop.bunnings.com.au/discussion/comment/119805#Comment_119805

Hi @matt234

That is an excellent diagram of the retaining wall. Since you now have an idea of the measurements, I suggest purchasing a few red bricks and Versawall blocks to get a real time feel of how the blocks will look like when placed into position.

Please keep us updated with your progress, we look forward to seeing your retaining wall built.

Eric

https://www.workshop.bunnings.com.au/discussion/comment/128596#Comment_128596

One final question. When I make the forms for my footing how do I get it to match up with the rough footing already there from the patio wall (assuming I go with jacobz suggestion to match them)? Do I try cut the old one flat or just have an open end on the forms butted up as close as I can and accept that some of the cement will run out?

https://www.workshop.bunnings.com.au/discussion/comment/134230#Comment_134230

Evening @matt234

Id probarly butt the ends up as close as possible, Its going to be hidden below ground so it dosnt matter if its not perfect. Ive used the shiny side of a cornflake box on a concrete repair to stop it oozing out, Ive also used silastic to caulk next to the form.

Dave

https://www.workshop.bunnings.com.au/discussion/comment/134230#Comment_134230

Hi @matt234

I think @Dave-1's suggested solution just nails it. The carboard should be more than enough to hold the concrete in place. I was thinking of using newspaper in a large amount, but cardboard is best, and it won't add a great deal of thickness to the concrete.

If you need further assistance, please let us know.

Eric

https://www.workshop.bunnings.com.au/discussion/comment/137803#Comment_137803

@Dave-1 I Love it. Will have to try out other cereals though, been too long since I had cornflakes!

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/140232#Comment_140232

Hi @matt234,

As @Dave-1 has said, you should leave the forms open-ended and butt them up against the existing foundation.

There might be a small amount of seepage, but it would be extremely minor. Just make sure to brace the forms very well where you leave them open-ended, otherwise the weight of the concrete can push them out, meaning you'll have a lot of seepage.

A stake no more than 50mm from the open end of the form would do this well.

Let me know if you have any further questions.

Jacob

https://www.workshop.bunnings.com.au/discussion/comment/141977#Comment_141977

Thanks @JacobZ, I went in to get supplies today and they didn’t have the timber I was planning to get. The guy said I could use plinth board instead of structural which was the other stocked option, so I got 150x25 plinth and some extra stakes to support the longer spans. But looking at it now I’m just sure it’s going to get stuck to the concrete because it’s so rough. Am I right to be wary or will rough boards work okay?

https://www.workshop.bunnings.com.au/discussion/comment/143249#Comment_143249

Evening @matt234

I had the same concerns when I was hunting for something for my formwork. I ended up using some melamime. It worked well. Tho my job was smaller then yours.

Dave

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/143249#Comment_143249

Hi @matt234,

I completely understand your concern, but I don't think it's going to cause too much issue as long as you let the concrete set sufficiently before removing the forms.

If you were looking to pour an appearance-grade concrete slab, where the sides of the slab are visible, you wouldn't use anything too rough, but in your case, it shouldn't matter.

Large commercial concrete pours use shuttering oil to create a barrier between the formwork and the concrete. Think of buttering a cake tin as an example. Oiling your formwork with some vegetable oil will allow you to remove the formwork much more easily.

Let me know what you think.

Jacob