David Dodd looks at what you need to know for exterior steps
Step design and construction has been a central topic for nearly every garden design course I’ve ever taught on. It’s quite unusual to have a perfectly flat garden and almost every project will require some form of step construction, whether it be a single step leading into a house or several flights leading from one end of a garden to the other.
Figures & measurements
The first point to consider for designing steps is how to get from point A to point B. This involves two measurements, height (the total rise) and distance (the total going). Once you have these figures, you can start to calculate the number and size of steps required. There are maximum and minimum dimensions for steps, and although there are different opinions on what these are, it’s usually somewhere between 75mm to 200mm ‘risers’ and 280mm to 600mm ‘treads’ or ‘goings’.
In my opinion, 75mm is more of a trip hazard than a step, and I find 280mm awkward (especially with my size 13 shoes). Steps should be comfortable to walk up and down, so I aim as close as possible to 150mm risers and 450mm treads. If the design permits and you can use a little bit more distance over the total ‘going’ to achieve this, all well and good, but if not, don’t worry – it’s okay to have non-standard unit dimensions to make the flight of steps fit.
The most important factor is to ensure that all the steps are equal in size. If you have even just one step slightly higher or lower, it’s likely to make the user stumble and possibly fall. If a flight is going to be more than 14 steps, a ‘landing’ needs to be incorporated. This is essentially an extended tread (minimum 900mm deep) and should be positioned halfway in the flight.
The second point to consider is construction. Safety is of paramount importance and steps should always be built to a very high standard. Ensure proper foundations are incorporated. If this is to be a poured concrete mass, reinforcing mesh will be required for improved tensile strength. Specify high-bonding mortars with the inclusion of styrene butadiene rubber (SBR) and apply a slurry mix to the back of the treads. This can be just neat cement and water, or again, consider adding SBR.
The step treads should always have a fall on them (approx 1:80) to shed water as quickly as possible, but without them becoming too much of a slope. This is particularly important in winter to prevent any excess water freezing, making the steps icy.
If bridging the damp proof course (DPC) of a building, a vertical damp proof membrane should be sandwiched between the step and the wall. The section of wall being covered by the step can also be painted with a bitumastic paint.
For sleeper steps, I recommend fixing them with metal strapping to 16mm steel reinforcing bar, which can be set in concrete. This is much stronger than using timber pegs, which will eventually rot. I’m not a huge fan of sleeper or timber risers with gravel treads – they can be in keeping if the design is more rural, but if the gravel migrates or settles, it can leave a lip that becomes a trip hazard, especially when walking down. Consider using a stabilising system such as Nidagravel to keep the gravel in place.
Steps can, and should, be beautiful, and where steps are required there is the opportunity to create a stunning design feature. Unless you are using bog-standard unit materials, many steps will need to be a bespoke order, which is why I mentioned not worrying about standard sizes earlier. If they are to become a major feature of your garden design, consider how you would like the risers and treads to be finished.
If using blocks of stone, the front edge of the block can be chamfered or pencil-rounded to take the sharpness off. If not a solid block, the tread may overhang the riser – this is called the nosing and shouldn’t be more than 25mm or it may become a trip hazard when walking up, especially for those of us with bigger feet.
A drip channel can be cut along the length of the overhang on the underside to prevent water running down the face of the riser via capillary action. Bullnose is a popular finish, as the rounded edge will prevent more serious injury should someone fall, hence the reason it’s commonly used for swimming pool coping. It’s also worth using a thicker stone for treads (40-60mm) as these will create greater drama than a thinner, standard slab.