Retaining Walls and Garden Steps: Drainage, Loading, and Design
A retaining wall is a structural element, not a decorative one. Underestimate the lateral earth pressure and it will lean, crack, or collapse.
Sloped gardens are common across Kent, particularly on the North Downs escarpment around Boxley and Detling, and in the Weald south of Maidstone. A well-designed series of retaining walls and steps can transform an unusable slope into a terraced garden with distinct planting zones, seating areas, and level surfaces for dining or play.
Lateral Earth Pressure
A retaining wall is not just holding back soil. It is resisting a force that increases with depth. A 1-metre high wall retaining saturated clay is dealing with roughly 15 kN per linear metre of lateral force. That is about the weight of a small car pushing sideways against every metre of wall. This is why retaining walls need engineering; a standard half-brick garden wall built on a shallow footing will not survive.
Drainage Behind the Wall
Water is the enemy. Without drainage, hydrostatic pressure builds behind the wall and can double the lateral force. We install a filter drain (100mm perforated pipe wrapped in geotextile, surrounded by clean 20mm gravel) along the base of the wall, with weep holes at 1.5-metre centres through the wall face to allow water to escape.
Step Design
Comfortable garden steps have a riser height of 150mm and a tread depth (going) of 350mm to 400mm. We build the risers from Class B engineering bricks (they handle constant moisture without deteriorating) and top them with natural sandstone or limestone slabs, bedded on a full mortar bed. Each tread should overhang the riser by 25mm to cast a shadow line that makes the steps easier to see.
See our article on combining brick and stone for more material ideas, or view our garden wall services.