PUBLICATIONS

Issue 32 - Winter 2004

On The Technical Side: Garden Steps

When on site for the first time, one of the initial aspects you notice is the relief of the site. Even the slightest slope can incorporate a step, or a false change of level like a sunken garden can be introduced if the water table allows. I always enjoy the challenge of level changes; these can be explored by using retaining walls, banks, ramps and steps.

Outdoor steps should be comfortable to use with consistent treads and risers.

The comfort and safety of a flight of steps depends on the passage width, the total run and the relationship between the risers and the treads.

The riser should not exceed 150mm or be shallower than 75mm with 110 mm being the ultimate leisurely riser. Treads should not be less than 300mm or more than 500mm. If wider they should accommodate a stride.

The following is a formula for calculating a step to riser ratio:

2R + T = 685mm (R=Riser and T=Tread)

For example:

2 x 150mm + 385mm = 685mm
The riser = 150mm and the tread = 385mm

When designing a set of steps (this depends on the function and the context) assess each situation separately. Measure the level difference between the top and bottom of the proposed steps. This is known as the total rise. Divide this by the suggested riser. For example, 150mm divided into 450mm will give 3 steps. Then apply the formula as above to give the tread. Multiply the number of treads by the depth of the tread and this will give the total run.

385mm(tread) x 3(number of steps) = 1.155 m - this is known as the total run.

The choice of the size of the passage width depends on the amount of traffic. For one person allow 1.2m. For two people abreast allow 1.5m and for each extra person add on an extra 600mm. Due to the increased sense of scale outdoors, widths and runs need to be wider due to encroaching planting .
The minimum number of steps is 3, though steps of 2 and 1 are not uncommon provided that they are obvious, like at a change of material. If not, one step can become a trip. Work with materials when calculating a step; this saves cutting materials .

To make a step more obvious and to produce a shadow line, an overhang of 25mm is recommended.

Figure1: Working wiht materials
Cross section showing brick riser and concrete slab tread

On long flights there should be no more than 14 steps between landings, though aesthetically in a garden situation 4 or 5 steps is preferable between landings.

In some situations, handrails may be required. They should be positioned not less than 840mm or more than 1m measured vertically above the nosing.

Good lighting is necessary in well-used areas. The lights can be recessed on the flanks of walls or in the risers.

Good surface drainage is essential. A forward slope of the tread at a gradient of 1 in 80 will stop the lodging of water and therefore ice.

A slip-resistant surface is desirable and solid steps of a hard stone such as granite is sound and also frost proof, giving high quality and performance. For steps of stone or brick a sound concrete foundation with an adequate toe is essential to stop slippage.

A slightly rounded nosing reduces chipping and retains a crisp appearance.

Riser	the height from one step to the next
Tread	the depth of a single step
Nosing	the shape of the front edge of the step
Total Run	the depth from the first step to the last
Passage Width	width of the step
Total Rise	height of all the steps

Figure 2: Step terminology

Diagrams: Aaron Rogers

References:

* Landscape Design Guide Vol 2 - Hard Landscape
* Complete Deck Book
* Landscape Techniques

Lisa Murphy, MGLDA

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