Sloping Gardens: Terraces, Levels and Retaining Walls

A sloping garden has potential that a flat one does not: views, shape, places to sit at different heights. It also has problems that appear only when you start to use it, such as furniture that will not stay level, lawns you cannot mow safely and rain that heads straight for the house.

The answer is almost never to fight the whole slope. It is to decide which parts you need to be level, which you can leave as they are, and how the water and the people will move through the space. This guide takes that in order.

Assessing the slope before you design

Start by understanding what the ground is doing. Walk the garden after heavy rain and note where water runs, collects or seeps out. Check which way the slope faces, where the house sits relative to it and whether neighbours' land is higher or lower. Plots in hilly areas such as those near the Malvern Hills can slope in more than one direction, which complicates things.

Then decide what you want to do on the garden. A seating area and a flat lawn want level ground. A path, planting and play area can often cope with a gentle fall. The more levels you ask for, the more earthworks and retaining you will need.

A simple way to measure a slope is to use two stakes, a string line and a spirit level, and to measure the drop over a known distance. A sketch with a few spot heights across the plot is often more useful than any single figure, and it is the first thing we would ask you for.

• Where does water go in heavy rain?
• Which areas must be level, and which can stay sloped?
• How steep is the fall, and is it uniform?
• What is above and below you: house, boundary, neighbours?

Cut and fill

The simplest way to create a level area is to cut into the slope at the top and use the soil to fill at the bottom. In theory this balances. In practice, soil expands when it is dug, topsoil should be saved, and filled ground settles unless it is compacted in layers. Building a patio or a heavy structure on loose fill is asking for trouble.

Cut and fill also creates banks. A bank that is too steep will slump, wash out and be hard to plant or mow. Either keep banks gentle, or hold them back with a wall.

Saving the topsoil matters. Strip it first, store it separately, and spread it back on top once the levels are built. Burying good topsoil under subsoil makes planting and lawns far harder later.

Terraces and retaining walls

Terracing breaks a slope into a series of flat steps, each held by a retaining wall. Low walls, built from block, brick, stone or sleepers, can often be done as part of normal landscaping. They need solid foundations, a free-draining backfill and a way for water to escape, because retained soil that fills with water pushes much harder on the wall.

Taller walls, walls that support a driveway, a building or a neighbour's land, and anything built close to a boundary should have an engineer's input. This is not a place to guess. We will tell you plainly when a wall goes beyond ordinary garden work and needs proper design.

Sleeper walls and timber crib walls suit lower, informal terraces and planted slopes. Block and brick walls give a more formal finish and can be faced to match the house. Stone walls bring the most character but need skilled construction. Pick the material to suit the height, the load and how long you expect it to last.

Drainage uphill and downhill

Water is the main risk on a slope. Whatever falls on higher ground, and whatever comes off the house, roof and any hard surfaces, has to be carried away without eroding soil or flooding the lowest point. Uphill, a land drain or a gravel-filled trench (a French drain) can intercept water before it reaches a terrace or wall.

Behind each retaining wall, use clean free-draining stone and a drain pipe leading to a safe outlet. Do not point drainage at a neighbour or the house. Where the ground does not take water well, a soakaway may not work, and you may need a different outlet.

Surface water from the house roof is easy to overlook. Check where downpipes discharge and make sure they do not run onto a slope that is already carrying water. Ask your local council or water company if you are unsure where a drain can be connected.

Steps, paths and lawns on slopes

Steps and paths join the levels together. Make routes that suit how you actually move: bins, mowers and shopping all need to get from one level to another. A gently angled path can be easier than a straight flight of steps, and landings give you somewhere to pause.

Lawns on slopes are tricky. Steep grass is hard to mow safely, dries out quickly and can wash away in storms. Keep lawn to the flatter areas, and plant the steeper banks with ground cover, shrubs or grasses that hold the soil. Where a bank must be grassed, keep it gentle enough to mow without slipping.

Planting on slopes helps in a quiet way. Roots hold the soil, leaves slow the rain, and mulch stops the surface being washed away. Low evergreen cover is more reliable on a bank than a lawn that must be mown.

Safety and phasing the work

Safety is not only about steps. Open drops need a barrier or planting, retaining walls need to be stable, and surfaces on slopes need grip. If children or older relatives use the garden, say so early so that the design suits them.

Slope projects are well suited to phases. Start with groundwork and drainage, which are hard to change later, then retaining walls, then steps and paths, then hard surfaces, and finally planting and lawns. Doing this in order avoids digging up finished work. A free site visit is a sensible way to see the whole plot and plan a sequence.

Be wary of work near boundaries. If a wall or a regrade changes how much soil presses on a neighbour's fence or garden, talk to them first and make sure the structure will not move. Ownership of boundaries depends on title deeds.

• Phase 1: drainage, levels and any required engineering.
• Phase 2: retaining walls and steps.
• Phase 3: paving, paths and structures.
• Phase 4: planting, soil and lawn.