Retaining wall basics

Retaining walls can be tricky to build as they need to be strong enough to resist horizontal soil pressure where there are differing ground levels.

One of the things you must get right is the thickness of the wall. It should be at least 215mm thick and bonded or made of two separate brick skins tied together.

This should be enough in most cases with minimal water pressure or where the ground level difference is less than a metre.

You also need to consider the effect of ground water, which can create huge pressure on the wall and soak the brickwork if allowed to accumulate behind. Create a way out for the water by adding a gravel trench and pipes through the wall.

If not properly constructed, water can also penetrate the brickwork structure from above through the mortar joints, affecting the long-term durability of the retaining wall. So add brick copings, which must always be F2, S2 (frost-resistant low soluble salts), with an overhang and drip groove to minimise water damage.

Important points about retaining walls

• Don't forget to include movement joints in the wall and use piers on either side to increase strength at the movement joint position.
• If you're using two separate brick skins in stretcher bond, you have to provide reinforcement by tying them together. Use stainless steel bed-joint reinforcement every third course to boost the strength.
• Use a high-bond damp proof course below the capping/coping and sandwich the DPC in mortar.
• Waterproof the retaining side of the wall and allow water to drain away from this side through weep holes/pipes.
• Slope paving away from the wall and provide gravel drainage strips where possible.
• Don't forget to protect waterproofing from damage while you’re building.
• Don't build higher than one metre without involving a structural engineer.

Want to find out more about this type of work? Visit these links:

• Brick Development Association
• The do's and don'ts of freestanding brick walls
• The danger of free-standing walls
• Wall repair basics
• How to get it right: Supporting joists on external walls

Please Note: Every care was taken to ensure the information was correct at the time of publication. Any written guidance provided does not replace the user’s professional judgement. It is the responsibility of the dutyholder or person carrying out the work to ensure compliance with relevant building regulations or applicable technical standards.