Holding back the ground
On sloping plots, a retaining wall creates level areas for gardens, parking and building. Newcastle and the coastal strip have many sites with steep gardens, terraced lanes and level changes between properties. Soil behind a wall is heavy, and when wet it pushes harder, so these walls fail if they are underbuilt or undrained.
Why retaining walls fail
- No drainage, so water builds up behind the wall
- Foundations too shallow or too narrow
- Walls too thin for the height of soil retained
- Weak mortar or unsuitable materials
- Tree roots or vehicle loads behind the wall
- Age, frost and weathering of masonry
Leaning, bulging, cracking or stepped sections are all warning signs. A failing retaining wall can be dangerous and may affect neighbouring land, so it should not be ignored.
Building a new wall
Good retaining walls begin with proper foundations, suitable reinforcement and wall thickness for the height. Behind the wall, a layer of free-draining stone and a perforated drain carry water away, with weep holes through the wall to relieve pressure. Waterproofing the back face and an appropriate coping protect the structure. Materials vary, including reinforced blockwork with a brick or stone facing, concrete, or natural stone, depending on appearance and loading. Higher or heavily loaded walls should be designed by an engineer.
Repairing existing walls
Repair depends on the fault. Small defects can be repaired by repointing, replacing masonry and adding drainage. Walls that have rotated or deformed may need partial or full rebuilding, with the soil temporarily supported. For repointing ideas, see lime mortar repointing. For boundary walls that do not retain soil, see boundary wall rebuilding.
Permissions and neighbours
Walls over a certain height, or close to boundaries, can need planning permission and Building Regulations approval. If the wall is on or near a boundary, the Party Wall etc. Act 1996 may apply. Guidance is at the Planning Portal and GOV.UK.
Frequently asked questions
Why do retaining walls need drainage?
Water trapped behind a wall adds large pressure and is a leading cause of failure. Drainage stone, perforated pipes and weep holes let it escape safely.
Do I need an engineer for a retaining wall?
For taller walls, walls supporting buildings, roads or heavy loads, an engineer is advised. For low garden walls, we can often build to standard good practice, and we will tell you if an engineer is needed.
