Estimate blocks or sleepers, backfill gravel, drainage pipe and concrete footing for a retaining wall.
You get the wall face area, the number of blocks or sleepers, the concrete for a strip footing, the free-draining gravel backfill behind the wall, and the length of perforated drainage pipe. Proper drainage behind a retaining wall is essential to relieve water pressure.
Note: walls retaining more than about 1–1.2 m of soil, or near structures, may need engineering design and building approval. Always check local requirements.
Yes. A layer of free-draining gravel and a perforated land drain at the base relieves water pressure, which is one of the main causes of retaining wall failure.
As a guide, a strip footing roughly twice the wall thickness and 150 mm deep suits low garden walls. Taller walls need a wider, deeper engineered footing.
Rules vary by area, but walls retaining more than about 1–1.2 m, or near boundaries and buildings, often need design checks and approval. Check with your local authority.
Yes. A gravel drainage layer and a perforated pipe behind the wall relieve water pressure that could otherwise push it over. The estimator includes these.
As a guide the footing should sit below the frost line and be roughly as deep as the wall is wide; taller walls should be designed by an engineer.
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