Do retaining walls need Building Regulations approval?

Retaining walls over 1.2m high or those supporting a surcharge (like a driveway or building) require Building Regulations approval. Walls under 1.2m in gardens generally don't need approval, but must still be structurally sound. Always check with your local Building Control.

What type of bricks should I use for a retaining wall?

Use engineering bricks (Class A or B) for all below-ground courses and the first 150mm above ground. Engineering bricks are frost-resistant and have low water absorption. Facing bricks can be used above this level for appearance.

How thick should a brick retaining wall be?

For walls up to 600mm retaining height, a single brick (215mm) may suffice. Walls 600mm-1m typically need 1.5 brick thickness (327mm). Over 1m, consider double brick (440mm) or reinforced concrete block construction with professional design.

Do retaining walls need drainage?

Yes, drainage is critical. Install weep holes (50mm pipes) every 900mm-1200mm along the base. Add a gravel backfill layer (150-300mm) behind the wall with landscape fabric to prevent soil clogging. Poor drainage causes hydrostatic pressure that can collapse walls.

How deep should retaining wall foundations be?

Foundations should be at least 450mm deep and extend 150mm beyond the wall on each side. Width should be 2-3x the wall thickness. For walls over 1m or in clay soil, foundations may need to be 600mm+ deep. Always below frost line.

Can I build a retaining wall myself?

DIY is suitable for small retaining walls under 600mm holding back garden soil. Walls 600mm-1.2m require good construction knowledge. Over 1.2m or supporting structures should be designed by a structural engineer and built by professionals.

What is the maximum height for a DIY retaining wall?

Most building experts recommend a maximum of 1.2m for DIY brick retaining walls. Beyond this height, the engineering becomes complex and failure risks increase significantly. Professional design is strongly advised for taller walls.

How much sand and cement do I need for a retaining wall?

For retaining walls, use a stronger 3:1 mortar mix. Allow 50kg of building sand and 17kg of cement per square metre of wall. A 6m x 1m retaining wall needs approximately 0.3 tonnes of sand and 4 bags (25kg each) of cement.

Do I need steel reinforcement in a retaining wall?

Brick retaining walls under 1m typically don't need reinforcement if properly designed. Taller walls or those with surcharge loads often require steel reinforcement or should be built with reinforced concrete blocks with filled cores.

How much does a retaining wall cost per metre?

Budget 200-400 pounds per linear metre for a 1m high brick retaining wall including materials, drainage, and labour. Costs increase significantly with height - a 1.5m wall may cost 400-700 pounds per metre. Engineering design adds 500-1500 pounds for the project.

Back to Brick Calculator

Brick Calculator for Retaining Walls

Building a retaining wall to hold back soil or create level changes? Calculate exactly how many bricks you need including engineering brick requirements. Our calculator accounts for wastage, drainage considerations, and UK Building Regulations guidance.

Bricklaying Materials Calculator

Calculate cement, sand and mortar using standard 4:1 ratio

1. Material Type

2. Wall Length (metres)

3. Wall Height (metres)

4. Waste Factor: 10%

Typical: 10% standard, 5% simple work, 15-20% complex patterns

Tips for Retaining Walls

Retaining walls over 1.2m typically require Building Regulations approval
Always use engineering bricks (Class A or B) for below-ground courses
Include weep holes every 1m for drainage - critical to prevent hydrostatic pressure
Consider concrete block construction for walls over 1m - stronger and more economical

Understanding Retaining Wall Construction

Retaining walls hold back soil to create level changes in a garden or prevent erosion. Unlike freestanding walls, they must resist constant lateral pressure from the soil behind them, making proper construction and drainage critical for long-term stability.

How Many Bricks Per Square Metre?

Standard UK bricks measure 215mm x 102.5mm x 65mm. When laid with 10mm mortar joints, this equates to 60 bricks per square metre for a single-skin wall. Retaining walls often require thicker construction.

Mortar Requirements

Retaining walls need a stronger 3:1 mortar ratio (3 parts building sand to 1 part cement) due to ground contact and moisture exposure:

50kg of building sand per square metre
17kg of cement per square metre
Add waterproofer to the mortar mix

Example Calculation

For a 6m long x 1m high retaining wall (6m2):
- Bricks: 6 x 60 = 360 bricks (+ 10% waste = 396 bricks)
- Engineering bricks for base: approx 108 bricks
- Sand: 6 x 50kg = 300kg (0.3 tonnes)
- Cement: 6 x 17kg = 102kg (5 x 25kg bags)

Common Retaining Wall Projects

Low Garden Terrace (0.6m)

Raised beds, small level changes

- 36 bricks per linear metre
- Single brick thickness OK
- Basic drainage required

Standard Retaining (1.0m)

Garden terracing, driveway edges

- 60 bricks per linear metre
- 1.5 brick thickness recommended
- Full drainage system needed

Tall Retaining (1.2m)

Maximum DIY height

- 72 bricks per linear metre
- Double brick or block required
- Building Regs may apply

Structural (Over 1.2m)

Professional design required

- Engineer calculation needed
- Reinforced construction
- Building Regs mandatory

Frequently Asked Questions

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