FAQ

What is a retaining wall?

It is simply a structure that is designed to hold the soil behind it, making allowances for proper drainage.

Why do I need one?

Firstly, you might not! Let us go through that with you, but there are other ways (see below). If you do need one, they're a great way to make additional useable space in your yard. Lots are getting smaller in Brisbane and Gold Coast, with land a premium, and any additional flat space you can create for your family increases the value of your yard.

What types of retaining walls do you build?

At Brisbane Retaining Builders, we specialise in sleeper retaining walls, as well as link block or sandstone block retaining walls. We find that these two general options are the most cost effective and suit 98% of people. The other option we generally don't do is a besser block wall core filled wall, as we won't be as cost effective as other companies in doing these (we can if you really want..).

 

What if I need a fence too, can you do that?

Of course, we offer a combined solution as we know most customers need a fence on top of their retaining wall. If we do a sleeper style retaining wall, we can install brackets that the fence mounts to, ensuring that the fence is easier to install and can also be easily removed later for replacement if needed. It's a great solution and looks neat.

 

What if I don't want or can't afford a retaining wall, what other options do I have?

Sometimes, you can create nice slopes instead, although these do take up more space, and you need to be mindful about soil erosion and weed growth. We can discuss this with you, and even build it for you with our earthwork machinery. Sometimes these can be much more cost effective depending on your situation.

 

Why do walls need to be engineered? What's involved?

Good question. It's easy to think you can just put some blocks there and they'll stay forever. The key to engineering is to guarantee the wall will stay for the design life, and build it in the most cost effective way. Engineering ensures it's not 'overengineered' nor 'underengineered'.

The engineering design process includes doing soil testing to confirm the type of soil, as this will dictate the footing requirements needed. For example, if you have very soft soil, you will require larger footings than if you are building in very hard strong soil.

Secondly, the footings are designed to withstand the force of the soil (and water, and other structures) that are pushing against the wall. That's why non-engineered walls can't have anything within 1.5m as that provides extra forces onto the wall. An engineered wall can technically have a road built right next to it if that's what has been designed for!

Lastly, overall stability checks are performed to ensure the wall doesn't slide (believe it or not they can), rotate, or crack. You might have seen many walls with cracks through them, or walls that have bowed in the middle. This is the result of having too much pressure (ie holding up too much soil) for the strength of the wall.

Engineers who perform regular retaining wall designs have this process very well established and can do it quite quickly. We can advise whether your wall needs engineering (most don't), and what can be done to minimise the cost involved.

 

Do you offer custom designs?

Every design is custom in the sense that every wall is different. The variety of blockwork and sleepers that are on the market now is enormous, and we aren't necessarily tied to any type of manufacturer, although we do have our recommendations.

 

What materials are best for my wall?

It will depend on your situation architectural style, however we highly recommend the following;

• Concrete sleeper and galvanised post retaining walls for their proven durability and longevity.
• If you want a cheaper option, timber sleeper walls can be slightly more cost effective, but we again highly recommend at least using galvanised posts. That way, you can easily replace the sleepers in 10-15 years when they rot, but the posts will still be structurally sound. If you really want to save costs, a full timber wall is still ok and will last, but not as long
• Any of the block walls are extremely durable, but you have to think about cleaning. The rough textured faces tend to attract mould if not cleaned regularly, and the curved faces are harder to clean.
• For block walls, link block range is fantastic and doesn't take up as much space as a sandstone block wall, however also can't be built as high, and might not suit your architectural style as sandstone looks fantastic when done right.

 

What if I have a large tree near my wall?

This can be an issue, as the roots of the tree will grow and potentially damage the wall. We can discuss this with you during our design process. Some wall designs will be less affected by the tree roots, while others will be heavily affected, again it depends how deep the roots are, and how established the tree is. We'll take all this into account and discuss with you.

 

What if I have an existing wall that's broken, can you remove it?

Yes, this is very common and we can dispose of it in an environmentally friendly way. We can also discuss replacement options to best utilise the space that was left by the old wall.

 

What if there might be some underground pipes nearby, or electrical cables?

The biggest risk with retaining wall builds is hitting an underground service (electrical, sewer, stormwater). We take care with this by using both the Dial Before You Dig service, and depending on the risk, undertaking our own underground detection methods using radar. This adds an additional cost in the order of a few hundred dollars, but it's essential for both our safety, but to ensure no underground services are damaged. If an underground service is damaged, it's very costly and sometimes even involves the service provider. We've never damaged anything, but it happens regularly in the industry due to lack of care and understanding.

 

How long do the retaining walls last for?

No one can specifically say, because every site is different. To give a rough answer, expect the following;

Timber sleepers - pine = 5-15 years

Timber sleepers - hardwood = 15-25 years

Concrete sleepers with galvanised posts = 30-50 years

Composite sleepers = untested as they are a new product but expect 20-30 years

Sandstone = 50+ years

Link blocks = 30-50 years

 

How much does a retaining wall cost?

This is everyone's most important question, so we'll try take the time to answer it. For more detailed responses we can go through the various options during the design consult.

It's hard to say and hard to price as it generally depends on the project specifics including height, access, material selection, and length. For example, a 0.6m high sleeper wall that is only 6m long will cost a lot more per m2 than a 1m high wall 30m long, as you'll get better economies of scale (ie setup costs, equipment costs, concrete costs, labour costs) for the larger wall.

You might see very low rates being advertised on some websites, and these were probably pre-Covid, for cheap pine timber, and with a very large wall hence driving down the cost per m2.

Here are some guidances;

• Timber sleeper walls - $250-500/m2
• Concrete and composite sleeper walls - $300-800/m2
• Link / Sandstone block walls - $300-800/m2

On top of this, you may require engineering (budget $1000-1500) and certification (budget $1000-1500) and council permits.

For example, if you want a 10m long retaining wall that's 1m high, you could expect to pay between $5,000 up to ~ $15,000 depending on the site conditions, style of wall, whether it needs engineering, the amount of excavation required, access requirements, etc.

If you however want a 20m wall, it would be less than double that, due to the economies of scale.

We are very transparent in our pricing and design guidance, as we know this is the biggest restriction for most home owners, and are happy to work with you to design the wall right from the beginning to suit your budget and style.

 

How long does it take to build?

Some can be done within 2-3 days, but allow a full week in most cases. If you have an urgent requirement, let us discuss this with you and we can accommodate as much as possible.

 

What are the council rules in Brisbane?

Here is the link to the Brisbane Council website related to building a retaining wall;

Build a retaining wall | Brisbane City Council

In general, you will NOT need council approval (and this means certification and engineering) if your wall meets the following requirements;

Queensland building regulations advise you will not need building approval for a retaining wall if:

• there is no 'surcharge loading' over the 'zone of influence' for the wall (refer to definitions in the Building Regulation 2006 (Schedule 1 Section 3))
• the total height of the wall and of the fill or cut retained by the wall is no more than one metre above the wall's natural ground surface
• the wall is no closer than 1.5 metres to a building or another retaining wall
• it does not form part of the fencing for a pool.

If your project does not meet all requirements, you must prepare a building application for building certifier approval. You must give the certifier scaled and detailed plans prepared by a draftsperson or architect

 

What are the council rules in Gold Coast?

Here are the council rules for Gold Coast;

Retaining walls | City of Gold Coast

An extract from their website states;

Retaining walls need building approval, unless they meet all the following criteria:

• less than 1.0 metre high
• further than 1.5 metres to a building or another retaining wall
• only support the soil behind the wall, nothing above
• not part of a pool fencing
• combined wall and fence height are less than 2.0 metres
• not built over a service (sewer or stormwater)
• meets structural requirements
• not in an easement or covenant area
• meets earlier development conditions
• not in a waterfront or oceanfront setback area.

If you are unsure of these requirements a licenced contractor, designer, engineer or private building certifier may be able to help.

A side boundary setback should be a minimum of 600 millimetres to avoid maintenance or ownership issues with your neighbour.

Stormwater must be captured and piped to the kerb or stormwater system and cannot be concentrated onto your neighbour's property as a result of the work.

If your retaining wall affects your neighbour, you should speak to them before starting work. This helps avoid disputes or legal action.

 

What if my wall is over 1m high, or I want to build closer than 1.5m to another structure?

It's more complicated, because it requires approvals which means paperwork. Essentially you will need an engineer to design the wall, a drafter to sketch it up, and a certifier to approve the build, and get council approval. We can take care of the entire process for you and make use of our supplier relationships knowing you can get the wall designed right the first time to suit your budget, or you can go do the work and get us to build it for you.

If you have a wall that needs to be ~ 2m high, one alternative is to 'step' the walls back and build 2 x 1 m walls, at a distance of 1.5m to each other. This breaks up the look, and you can have plants in between the walls. This is a relatively popular way to 'avoid' the approvals, but be cautioned that it's not necessarily cheaper, because now you're building 2 walls, with double the preparation, and it might still be more cost effective to build 1 larger wall with the right approvals. We can discuss this during our design consultation.

 

What drainage is needed for my retaining wall?

Drainage is essential for a structurally sound retaining wall, for the durability to meet the design life, and for the aesthetics of the wall. We install a geomesh fabric, with a suitably sized drainage pipe, and backfilled with the correct free-draining material such as gravel. Some contractors only use the gravel, some don't use gravel at all and only install a pipe. As engineers, we know the reasoning for the drainage is to prevent a pressure build-up which will affect the forces on the retaining wall, and over time will make the wall shift during heavy rainfall when the ground is soft. Also, having the right drainage avoids the dirt washing through the gaps between the wall, which will be visible for the life of the wall.

This is one of the aspects of retaining wall building where many contractors skip, because it's not visible after the wall is built and no one will ever know. It's a very easy and cheap to do right the first time, and very costly to fix later.

 

What areas do you service?

We are based in Brisbane and Gold Coast, and service from Ipswich, Brisbane, Gold Coast, and down to northern NSW.

 

How do I get started - what's your process?

Step 1 - get in touch using our contact form and well give you a call (or email if that's better) to discuss the project.

Step 2 - we can give some design guidance over the phone or visit you in person to discuss the project in more detail

Step 3 - we can provide a preliminary budget and if that's suitable, we will visit site to provide a firm quote. This is involves quite a bit of work on our side to double check dimensions, check approval requirements, check the right type of wall and quote up the individual components. We rather quote wall by wall rather than a generic rate because it usually works out better for the customer as each wall is different.

Step 4 - if you accept the quote, we book in the agreed date and pay a deposit

Step 5 - If any engineering or approvals are required, we take care of this. We keep you informed throughout the process

Step 6 - We attend site to build the wall and clean up after it's completed. We keep you informed throughout the process to ensure you're aware of our movements and timeframes.

 

Do you offer a warranty?

Yes, as licenced contractors we are obliged to offer a warranty against defects. These will depend on the wall choice and we can discuss this with you during the design consultation.