Planters on sloping or uneven ground

Background

As with so much in design, there are no ‘perfect’ solutions to this challenge – merely more, or less, optimal solutions, to a given brief.

The background context is key. For example:

• Adjusting a standard, geometric planter design to cope with a slope or uneven ground will always come with a cost. Whether that additional cost is justified will be judged against a basket of considerations – such as the severity of site conditions, client expectations, the budget available, the desired design life of the planting installation etc.
   
• The impact of falls will depend on the scale of the planters. A fall over the length of a planter of [say] L 2000mm may be aesthetically acceptable; whereas a fall over the length of a planter of L 10000mm may not be acceptable.
   
• What is deemed to be ‘acceptable’ will itself depend on the brief. For example, the cheapest solution to these challenges is to simply incorporate adjustable feet into the base of the planters – but that will often leave varying gaps under different faces of planters, and the feet may even be visible at ground level. In busy public realm spaces, who is really going to notice these imperfections…? But, in a high-end residential development, these imperfections may not be acceptable.
   
• Even in public realm, what is aesthetically acceptable may not be acceptable on other grounds. For example, there may be the requirement to close up any large gaps for Environmental Health reasons.
   
• As would be expected, the more extreme the site conditions, the more expensive will typically be the solutions to address them. Therefore, in some sites, falls may not be an issue to ‘mitigate’, but these falls themselves may drive the design. Worst case: if the falls are not adequately considered in design, then tidying it all up after the event can prove extremely expensive.

Given all of these, and other, considerations, the following is by no means a definitive list – but it does include some of the most commonly specified design options, which we hope will provide a useful guide.

Options are ordered according to site conditions – from the least severe, to the most severe. We have also ordered the Image Gallery to follow the same sequence.

B. Significant falls

There are situations where adjustable feet, with or without a skirt, are really not going to meet the requirements of the brief. These situations include:

• Very large planters spanning large falls – where it is not acceptable for the weight to be point-loaded onto adjustable feet [either because the weights are simply too great for adjustable feet, or because there is a structural requirement to spread the weight more widely].
   
• Very long planters spanning large falls – where the end-to-end fall is simply too large to be compensated for by adjustable feet [typically anything over 150mm cannot be safely mitigated with feet alone].
   
• Where the planters need to look ‘perfect’ in relation to significant falls, and a skirt is not acceptable – such as in high-end residential developments.  

In such situations, there is the option to shape the bottom of the planter to the falls. This can be both extremely attractive and reasonably cost-effective, so long as falls can be surveyed and specified with a high degree of accuracy [for example, because falls relate to newly laid groundworks, with a near-perfect surface; or because the existing groundworks are fair, absent perhaps some minor shimming on site].

There are a couple of variants on this design option.

B.1. Planter Base Shaped to Falls

The simplest / cheapest option to mitigate significant, yet consistent, falls is to shape the base of the planters to the falls; so that the planter rims read as being horizontal, and the base is shaped to the ground.

Falls can be in multiple directions; and that need not have a material additional cost impact, so long as all details are clearly specified, and incorporated within the planter design model.

Projects where this option was specified include:
Berkeley Group - Royal Arsenal Riverside, London SE18
Lancer Square, Kensington, London W8
Torphichen Street, Edinburgh, EH3

B.2. Planter Plinths Shaped to Falls

In this more complicated / more expensive option, instead of the planter base being shaped to falls, a plinth is shaped to falls, onto which plinth the planter is bolted.

There are a number of reasons why this additional complexity / cost might be considered justified:

• In certain situations, it may be argued that a shaped plinth, combined with a symmetrical planter above, is simply more attractive aesthetically.
   
• Where underlighting is built into the planters, this is typically built into a plinth. And, where there are falls, it is also visually more pleasing to have the line of light reading as being horizontal, with the shaped plinth creating a shadow gap of varying height.
   
• In public realm, having a robust plinth can also be of benefit, where, for example, street cleaning machines are used.

In each of the above examples, the plinths are often painted out a darker colour, such as black – which works, in each case, for different aesthetic and practical reasons.  

Projects where this option was specified include:
Garryard House, Dublin 2, Ireland
Notting Dale Village Campus, London W11
Shepherds Bush Road, London W6

Finally, there will be other situations with significant falls where the ground is simply too complex for the planter bases to be shaped; or where the planters need to look ‘perfect’ in relation to significant falls – such as in high-end residential developments.  

There is a final option.

B.3. Planter ‘Buried’ Beneath the FFL

In this option, instead of the planter base being shaped to falls, the planter is of simple, rectilinear form, and is laid on a flat foundation under the FFL; and the FFL material, including its falls, are laid up to the planter. In effect, the planter is ‘buried’.

Obviously this option is not universally applicable, as it only works for schemes where the groundworks are being freshly laid, such as a new development.

Also the option might initially seem extremely attractive, but it is not without complexity and/or cost. Specifically, with any powder coated or painted metal, there needs to be a [say] 10mm minimum air gap all the way around the planter, to enable the planter wall to ‘breathe’ and not set up corrosion; and this is recommended even with Corten steel, to avoid there being an uneven line of patination at ground level. With most FFL materials [such as concrete, tarmac, resin bound gravel, paving], what this means in practice is that a protective barrier [such as a stainless steel edging] needs to fastened to a concrete foundation; completely encircling the planter [and itself laid to the correct falls], up to which the FFL material will be laid.

So this option is definitely in the design armoury. However it needs to be specified with caution and due consideration; and it is often not as simple – nor as inexpensive – as one might at first imagine.

Projects where this option was specified include:
Berkeley Group - Royal Arsenal Riverside, London SE18