Expert Retaining Wall Contractor Northern Beaches

The golden rule I follow for every Northern Beaches retaining wall is this: the base width should be at least one-third the height of the wall, but honestly, with our coastal soil conditions, I usually go wider. So if you’re building a 1.5-meter wall in Collaroy’s sandy soil, you’re looking at a minimum 500mm base, but I’d probably recommend 600-700mm for long-term stability.

But here’s the thing – that’s just the starting point. You also need to factor in our dramatic seasonal weather changes, the salt air that degrades materials faster, and those king tide events that can saturate soil unexpectedly. The real rule is: design for the worst conditions your site will face over 30 years, not just average conditions.

Staggering retaining walls – what we call terracing – is probably the most common solution for steep Northern Beaches properties. Instead of one massive wall that council won’t approve and would cost a fortune, we create multiple smaller walls that step down the slope.

The key is planning the terraces to create usable space at each level. Maybe the top terrace becomes a kids’ play area, middle level for entertaining, and bottom level for garden beds. Each wall needs its own drainage system, and they all need to work together hydraulically.

Spacing between walls depends on slope angle and intended use. For areas where people will be walking, I maintain at least 2 meters between wall faces. For garden areas, you can get away with less, but you need to consider access for maintenance.

Backfilling in Northern Beaches requires special attention because our soil conditions and weather patterns create unique challenges. Never use the excavated soil as backfill – it usually contains too much clay or organic matter that retains water and creates pressure.

I specify clean, free-draining aggregate for the first 300mm behind the wall, then transition to engineered fill material that provides good compaction but still drains well. In areas with high water tables or near the ocean, we sometimes use all aggregate backfill to prevent hydrostatic pressure buildup.

Compaction happens in layers – never dump and compact the whole backfill at once. Each layer gets compacted to 95% standard density, and we test random locations to verify. Poor compaction means settlement and potential wall failure later.

Height determination starts with understanding what you’re trying to achieve and what council will allow without major approvals. In Northern Beaches, you can usually build up to 600mm without development approval, though you still need engineering for anything substantial.

For practical purposes, I look at the natural slope, the desired final grade, and how much usable space you want to create. That steep Collaroy block might technically need a 4-meter retaining wall, but that’s expensive and requires complex approvals. Better to design 2-3 terraced walls that create more usable space anyway.

Consider maintenance access too – walls over 2 meters become harder to maintain, and in Northern Beaches where salt air accelerates weathering, maintenance access matters for long-term performance.

Regular stability checks are smart preventive maintenance, especially in our coastal environment where salt air and weather extremes accelerate wear. I recommend annual inspections looking for specific warning signs.

Check for any movement – use a level against the wall face to detect leaning, look for cracks in mortar joints or concrete, and watch for separation between the wall and adjacent structures. Even small movements can indicate foundation problems.

Drainage function is critical – after heavy rain, water should drain away quickly. If you see standing water or wet spots persisting days after storms, your drainage system might be failing. That leads to pressure buildup and eventual wall failure.