Upstairs, downstairs

In March this year, we took part in a challenge for Comic Relief attempting to climb the equivalent of Mount Everest at the historic Park steps in the centre of Nottingham. This was a huge undertaking as the steps are incredibly steep and uneven; they are hard to walk up and down let alone run. This got me thinking about the design of stairs and steps in the UK.

Staircases are a practical, maybe even mundane aspect of a property, but they can be dangerous places. Rather unusually, most countries don’t keep records of causes of falls. The last UK figures were recorded in 2002 and they showed that 306,166 people required medical attention for injuries sustained during a fall on stairs. They are the second most common cause of accidental death, less than car accidents, but more than those for drownings, burns or other hideous misfortunes.

We’ve all tripped or missed our footing on stairs from time to time. In fact, there are calculations for the likelihood of missing a step. When a trip does happen, we usually blame ourselves for our lack of attention, but design has a substantial effect on the likelihood of whether you will fall. You expect factors leading to a fall to include poor lighting, lack of a handrail or confusing patterns on the tread. Other factors which can interrupt the natural rhythm of ascent or descent are unusually high or low risers or treads that are wider or narrower than usual.

Taking particular care on staircases at the beginning and end of use is advised, as this is when we seem to be the most distracted. Going downstairs is understandably much more dangerous than going up, with over 90% of injuries occurring during descent. The steepness of the stair (pitch) is a crucial consideration to safety as we find different pitches difficult to navigate. Anything over 45 degrees is taxing to walk up and less than 27 degrees is very slow.

Surprisingly, architects had little to say about stair design until the late 17^th century, when Francois Blondel devised a formula to fix the relationship between riser and tread. He suggested that for every unit of increased height, the depth of tread should be decreased by 2 units. As far as stair geometry in the UK is concerned, the allowable step dimensions are controlled by the Building Regulations, specifically ‘Approved Document K: Protection From Falling, Collision and Impact’. These regulations control the height of the step (the rise) and the depth of the tread (the going) and the overall steepness of the stair (the pitch angle). They also state further criteria which constrains the relationship between the going and riser, namely:

• g+2r = 550mm to 700mm

This is the equation attributed to Francois Blondel, and is therefore still taken into consideration when designing stairs in the UK today.