Made of concrete, natural stone, or gabions. Retaining walls perfectly compensate for differences in garden height and protect slopes. Find out more about the best solution, what to look out for, and the expected costs.
Retaining walls are installed when, due to space or preference, you cannot or do not want to compensate for height differences in your garden with a planting slope.
One tall wall can be used to support a slope, or many smaller walls can be stacked to form a terrace, with many small flower beds, or a plot of flower beds planted in a row. Depending on their height, retaining walls in a sloping backyard are very demanding work and require certain requirements in terms of materials and construction.
Retaining Walls. A Brief Overview Of The Most Important Ones
Retaining walls are used to even out differences in garden height and to support slopes. A stable foundation, such as crushed stone or concrete, is essential. They also require gravel or crushed stone for backfill and, in the case of clay soil, drainage. Planting rings, natural stones, gabions, concrete stones, and L-shaped stones are suitable for retaining walls.
How Are Retaining Walls Constructed?
High retaining walls cannot be built as they are: from 120 cm, professional help is required, and from 2 m high, a structural engineer is needed. This also determines the dimensions of the foundation required. This is because the soil pressure on the wall should not be underestimated, as poorly planned retaining walls can buckle or break. It is a good idea to check with the building authority before building whether a building permit is required.
The actual construction of a retaining wall can be done by a skilled person – but it is a feat of strength, a job that breaks the backbone, and only makes sense up to a wall height of 120 cm. Otherwise, it’s better to have a gardener or landscaper do it for you.
The Key Is A Stable Foundation.
Depending on the soil, construction method, and wall material, the foundation should be either a gravel foundation or a concrete strip, which should always be somewhat wider than the lowest wall stone. The width of the retaining wall should be equal to one-third of its height.
The foundation always rests on a layer of compacted gravel for drainage and is often made of medium-strength Class C12/15 concrete. For small retaining walls, a 40 cm deep trench of compacted gravel and a 10-20 cm thick layer of concrete are usually sufficient to maintain the height of the wall.
Solid or mortar retaining walls over 120 cm high require strip foundations at least 80 cm deep to provide freeze protection. Gravity walls should be stabilized with footings about one-third the width of the wall. The space between the foundation and the slope should be left at 40 cm and backfilled there. The foundation should be made of wooden planks to prevent the soil from slipping.
Heavy Loads Are Required.
To withstand the soil pressure, the retaining wall must be heavy and sloped in such a way that the center of gravity is also sloped to the slope. The steeper the slope, the heavier the retaining wall has to be.
However, retaining walls not only have to cope with soil pressure but also rainwater and seepage water, which can easily wash away soil and damage the wall. For this reason, gravel or crushed stone is used for backfilling, and in the case of clay soil, drainage is also required to remove sediment water from the wall surface in the first place.
The drainage pipe required for drainage enters the gravel layer behind the foundation and ends at the edge of the wall or in the drainage channel.
What Type Of Backfill Material Is Required?
One side of the retaining wall will inevitably come into contact with the ground, so it must also face water seepage that threatens frost resistance. To prevent that water, drainage pipes are built at the base of the wall, depending on the soil conditions and the type of wall, which is especially necessary for structures that allow little or no water to pass through.
Backfill all types of retaining walls with a mixture of sand and gravel or chips. If possible, cover this layer with garden fleece towards the top, as this layer should still be covered with topsoil and the soil should not seep into the gravel. If there are voids in retaining walls, such as gabions or dry stone walls, the back side should also be protected with fleece to prevent soil seepage.
Planting Rings To Create Retaining Walls
Planting rings, planting stones, or embankment stones are concrete stones with an open top and bottom, available in round and square shapes. Round stones with grooves are particularly preferred for slope stabilization.
They offer a high degree of design flexibility and can be curved. However, the main feature of these stones is that they can be filled with gravel or soil and planted. This means they can be planted.
The filling can create a planting ring that is heavy enough to serve as a retaining wall and resists soil pressure from the slope. The individual elements are stacked compositely and can be slid back gradually from row to row so that the slope to the slope becomes visible. Only in this way, part of the stone is always exposed to allow planting from the start. A retaining wall made of planting rings requires 30 cm of compacted gravel and 10 cm of concrete as a foundation, 60 cm, and 20 cm respectively, from a height of 1m.
Place the first row of stones in the wet soil and concrete, so that the stones are halfway into the soil afterward. Important: Since the stones are exposed at the top, rainwater will enter them. Therefore, make drainage trenches under each stone with damp concrete to prevent water from accumulating on the bottom stone.
For water to drain well, the first row of stones should be filled with one-third gravel. If planting rings, fill them with soil. Planting rings are a fairly inexpensive retaining wall variant, but visually not to everyone’s taste: a single ring costs between EUR 2 and 3, while a larger one, 40 cm long, costs around EUR 8.