Hi Nick, 


I'm a little unsure of what exactly you want explained (are you wondering
why 150-170mm is recommended, or are you wondering why a particular range is
recommended in the first place), so apologies if my reply is very
simplistic. 


Firstly, it may have been a typo but the recommended rise of external and
internal steps is within the range of 150mm-170mm. Not 150mm OR 170mm, as
your query suggested. 


Many people experience difficulty walking up and down stairs. With regard to
the rise of a step, the height to which a person has to raise (or lower)
their leg when going up (or down) will make a difference to how
easy/comfortable it is to use the stairs. As the rise gets higher, the
strength required to use the stairs will also get higher. If you ever do the
Inca Trail you'll understand what I'm talking about. 

At the same time if the rise is too low, the staircase will take up too much
space within the building - and so a compromise has to be made. 

A rise range should therefore be chosen to maximise ease of use, while also
making best use of the space in a building. 

Now, how they came to the figure of 150-170mm specifically - I'm unsure. 

In a perfect world, research would have been conducted with a large sample
of people, including people with a range of ages (from children to older
people), sizes (range of heights and weights), and physical
abilities/disabilities. From this research, an optimum range would be
calculated, so that the maximum number of people is accommodated. 

Whether or not this sort of research was conducted for the 150-170mm
conclusion, I'm not sure - perhaps someone else on this mailing list can
answer that. 


Finally, BS8300: 2009 states:
"Excessively high risers can result in excessive strain being placed on the
knee and/or hip joints of ambulant disabled people, when descending flights
of stairs.
When ascending a stair, people who wear callipers or who have stiffness in
hip or knee joints are particularly at risk of trapping the toes of their
shoes beneath projecting nosings, and of tripping as a result. In addition,
some partially sighted people can feel a sense of insecurity when looking
through open treads, and assistance dogs might refuse to proceed.
The preferred dimensional ranges for steps and stairs are between 150 mm and
180 mm for the rise and between 300 mm and 450 mm for the going."


If I interpreted your query incorrectly, just let me know. 

All the best, 

Antoinette


_________________

Dr Antoinette Fennell

Research Fellow - Project Scientist - Universal Design

TrinityHaus

McNamara Centre for Construction Innovation and Sustainability

Trinity College Dublin

Dublin 2

Ireland

Tel: +353 (0)1 896 3720

Email: [log in to unmask]


-----Original Message-----
From: Accessibuilt list [mailto:[log in to unmask]] On Behalf Of
Nick Metcalfe
Sent: 26 June 2009 14:09
To: [log in to unmask]
Subject: Rise of Steps

Dear All,

sorry to bother you on a friday afternoon,
but i was wondering if anyone could tell me why according to part M and
other 
documentation the rise of a step should be 150mm or 170mm?

Many Thanks

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