Retaining wall or not?

Hi Simon! For a 30” (about 750mm) high brick wall retaining a lawn and supporting a patio slab, here’s what to consider:

Brick walls are not typically designed as retaining walls on their own, especially if they’re only one brick thick.

At that height, the soil pressure behind the wall can cause movement or failure if it’s just bricks laid without structural support.

A 100mm concrete “skin” or backing (a reinforced concrete retaining wall or a concrete backfill) behind the brickwork is a good idea to provide the necessary strength and resist soil pressure.

Alternatively, you could build a reinforced concrete retaining wall first, then build a brick veneer or cladding in front for aesthetics.

Proper drainage behind the wall is essential to reduce hydrostatic pressure, which adds stress.
If you want the wall to support a slab on top (like seating), the structure beneath must be stable and load-bearing, so concrete backing or a concrete footing is important.

Bottom line: For a 750mm retaining wall holding soil and supporting a slab, a concrete backing or reinforced footing is highly recommended for durability and safety.

Dig a foundation for the wall to sit on. Concrete with rebar in the foundation. Then build wall, and yes use concrete blocks.

Yes, it is best to build it double-skinned to help hold back the pressure.

Hello simon. I would suggest
Putting concrete blocks down the back. Not very expensive and really hold well

hi simon, if the garden is running to the new wall then you will need to, but make sure you put weep holes, infant of the blokes you could put some rubble or even lay the blokes flat instead of the 100mm way up. hope this helps

Yes you will need to build a 9 inch wall all way round block at rear and faced up with brickwork or block laid flat and face rendered

You could do either a block with brick face or double skin wall as single skin would fail with that sort of pressure/frost/expansion behind

For a 30” (750mm) tall lawn retaining wall, adding a concrete skin is a good idea for stability, especially if the wall will support a seating slab.

Here’s what I’d recommend:

1. Concrete skin: A 100mm concrete backing will help resist the soil pressure behind the wall and improve durability, especially with the added weight of seating.
2. Drainage: Include weep holes or a drainage layer (e.g., gravel and a perforated pipe) behind the wall to prevent water buildup, which can increase pressure.
3. Foundation: Ensure the wall has a strong footing; typically a 150–200mm thick concrete base.
4. Wall thickness: If you prefer not to add a concrete skin, use double-skin (215mm thick) brickwork with ties for added strength.

This approach ensures the wall will safely handle the load and last long-term.

Yes you would need a retaining wall if there is going to be weight put behind the wall

Block and render would be best but a double skin facing brick would be fine as well

Yes if there is soil behind the wall it needs to be a retaining wall to hold back the earth behind

Dear Simon,

When building a wall to retain a lawn area, particularly one with a height of around 30 inches (750mm), the need for additional reinforcement, such as a 100mm concrete skin behind the wall, largely depends on the type of load it will need to support and the specific ground conditions.

For a wall intended to support a patio slab and hold back pressure from the lawn, it’s important to consider the following:

Retaining Pressure: A concrete skin or a reinforced foundation can help counteract the pressure from the lawn, especially if the soil is prone to shifting or if there's significant moisture fluctuation. However, for a 30-inch wall, the pressure exerted is relatively manageable, so in many cases, a standard brickwork wall with adequate footings may be sufficient without the need for additional concrete behind it.

Wall Design: If you are adding a heavy slab or seating area on top of the wall, reinforcing the base of the wall may be necessary. A concrete foundation or additional reinforcement, such as a concrete skin, would provide better support, ensuring the wall can bear the weight without risk of settlement or instability.

Drainage: It's important to ensure proper drainage behind the wall to prevent water buildup, which could add pressure and affect the stability of the wall. Installing weep holes or ensuring good drainage around the base can help mitigate this.

Ultimately, if you are adding significant weight (e.g., the slab for seating), or if the ground conditions are less stable, the additional concrete skin could be a good option for reinforcement. However, for a typical low-height retaining wall, a well-constructed brick wall with proper footings may suffice if drainage is properly managed.

If you’re unsure, it may be beneficial to consult a structural engineer to assess the specific requirements based on the site conditions and intended use.

I hope this helps, but please feel free to get in touch if you have further questions.

30 inch is a lot of soil and dirt to hold back so a support for the wall will be required.
also a french stone fill drain at the rear of wall with drain hole outlets in the wall

Building a retainer in breeze block first will always take weight and help longevity of garden

For a wall holding back a 30” tall lawn, it’s best to build a sturdy retaining wall to handle the pressure from the soil. Adding a 100 mm concrete layer behind the brickwork will strengthen it, especially if you’re adding a seating slab on top.

To prevent water buildup, include drainage behind the wall, like gravel and small drainage holes at the bottom. If you’re unsure, it might be worth asking a structural engineer for advice to make sure it’s strong and stable.