Articles - Technical Design

Three ways to increase planting depth at roof level


How to increase planting depth at the roof level? The obvious answer would be to increase planter height but are there any other ways?

Roof gardens on new developments are becoming a must-have.  Now, these amenity spaces are becoming more sophisticated, with places to socialise, extensive planting and even outdoor cooking.  Mainly, planting at the roof level is achieved with a raised edge.  This forms a perimeter that retains soil.  Where greenery is appropriate, designers occasionally look to specify larger plants, mostly this is small trees which can add an interesting dimension to a space, invite wildlife and reduce pollutants in the air.  The main challenge here is the requirement for increased soil depth to accommodate large root formations.

The obvious solution is to increase the height of the Planter Edge.  This achieves a greater soil depth but can visually ‘take over’ a space as height increases.  The two other challenges with this are the added weight of the material required and the cost implications.

This article will discuss the 3 ways to accommodate deep planting without increasing planter height.

Soil Gradients – Increasing Planting Depth

The first approach to accommodate larger root formations without increasing planter height is to implement soil gradients. In this method, the soil within the planter is intentionally sloped upwards towards the base of the tree while keeping the planter’s height at a lower level. This sloping technique allows for greater soil depth where it’s needed most—near the tree’s roots.

By strategically adjusting the soil profile within the planter, you can create a natural transition that increases planting depth whilst blending in with the overall design of the rooftop garden.

Image showing how gradients can be used to increase planting depth.


Varying Planter Height – Increasing Planting Depth

Another way to achieve deep planting whilst minimizing the visual impact of taller planters is to vary planter heights strategically.  Using this method, most of the planting is designed at a low to medium height.  This keeps the space open and allows for low shrubs and vegetation.  However, where deep planting is required for trees or larger foliage taller planters are introduced to increase planting depth.

As shown below at 54 Wilson Street, this allows for larger plants without dramatically increasing the height of the whole edge.

How planter heights can increase depth

Build up, Going Down – Increasing Planting Depth

The final option that increases soil depth relates to the planter edge system.  Where a roof tray system is being used, vital depth is lost as soil is placed upon the raised floor.  By having the planter edge sit directly upon the insulation layer, waterproof layer or drainage crate, extra depth is gained.  Pedestal-mounted paving can then be butted up to the front of the edge.  This achieves greater depth below the surface without the use of excessively high planters.

By using a self-weighted system such as the Velox Rapid Edge, ( you can ensure that all possible depth is utilized as the soil is not unnecessarily raised onto a roof tray.

Hopefully, by now you have a comprehensive insight into the 3 main ways of increasing soil and planting depth at roof level without increasing planter height.


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VELOX Rapid Edge™ UK00003507705 - Registered Design Europe: 008214910 & UK: 90082149100001 - Patent no: GB2600394