Retaining Walls

Building retaining walls properly

A retaining wall holds back ground, and ground pushes hard, especially when it's wet. A wall that looks fine on the day it's finished can bulge, crack or lean years later if it wasn't designed and built for the load behind it. That's why we treat retaining walls differently from other walls.

Where a wall has been designed by a structural or civil engineer, we build it to the engineer's drawings and specification. That covers the wall thickness, block or brick type, mortar, reinforcement and ties, foundations, drainage behind the wall and weep holes, and the coping and damp-proofing details. If something on the drawings doesn't match what we find on site, we stop and ask the engineer. We don't substitute our own judgement.

When a wall needs an engineer

We are bricklayers, not engineers, and we don't give structural advice or size retaining walls ourselves. As a guide to when you'll need a designer involved:

• The NHBC Standards expect retaining structures more than 600mm high to be designed by an engineer on new homes they cover.
• Under section 167 of the Highways Act 1980, which applies in England and Wales, a retaining wall within 3.66 metres (4 yards) of a street that is at any point more than 1.37 metres (4 feet 6 inches) above the ground level at the street boundary can only be built to plans, sections and specifications approved by the local authority.
• Walls that support a building, a drive, a slope or another structure, or that sit near a boundary, will often need design input and may involve Building Regulations, planning or party wall matters.

If you're not sure whether your wall needs an engineer, ask your designer, building control body or local authority before you commission the work. Our blog post on retaining walls and engineer's designs explains this in more detail.

What we build

We build masonry retaining walls in brick, block or both: reinforced hollow blockwork faced with brick, solid brick walls, and brick-faced walls on engineered foundations. On housing developments that often means walls between plots on sloping sites, walls alongside drives and roads, and walls around car parks and landscaping. On private projects it can mean garden terraces, walls to level a driveway, or replacing a failed wall.

Whatever the wall, we pay attention to the details that keep it working: weep holes and drainage left open and clear, damp-proof courses where they're specified, movement joints at the spacings shown, and a coping that throws water clear of the face. The facing brick is built to the same standard as the houses around it.

Groundworks and drainage

Excavation, concrete foundations, and the drainage and backfill behind a wall are often carried out by groundworkers. We coordinate with them so the wall is built in the right sequence, for example not backfilling before the wall and its mortar are ready for it, as the engineer's method requires.

Materials for retaining walls

Retaining walls stay wet on the retained side for much of their life, so the brick, block and mortar need to suit that exposure. We use the materials the engineer or specification calls for, which is often frost-resistant bricks, suitable blocks and a stronger mortar designation, and we don't swap them for cheaper alternatives. Waterproofing or tanking to the back of the wall, where specified, is built into the sequence so it isn't damaged during backfilling.