It depends what you are trying to demonstrate. The Yorkshire TO Group
produced a table some while ago of species-specific shade intensities,
but I find it unusable in practice. Paul Littlefair won't touch tree
shade with a bargepole, and Richard Nicholson assured me that 5.3.1
would go when the BS was reviewed.
I can see the theoretical rationale behind the artificial shape when
offered as an "average" shade pattern. The problem is that there are so
many variables that I have not been able to relate it to design
discussion with architects.
Shade does need the understanding of the trees and the site-specific
manner in which they grow and/or have been maintained, and their
consequent growth form.
Probably the best example of how the 5.3.1 pattern can be so difficult
to apply is when a TCP is produced by a non-arb.
I use a shade pattern derived from the sun trace on the 21st June, which
is the least amount of shade. (I don't advocate this as the construction
limit!!). I consider all the other aspects and then discuss with
(confront!) the architect about how the presence of trees affects the
proposal. The outcome can be re-positioning, re-orientation, re-design,
or nothing.
BS5837 is guidance - the end product is all about justification.
The 5.3.1 pattern is not "accurate", but in all fairness it was never
intended to be. I certainly would not condemn its use if logically
justified, but it's not for me.
Jim
-----Original Message-----
From: Dom Scanlon [mailto:dom@xxxxxxxxxxxxx.com]
Sent: 04 August 2009 16:57
To: UK Tree Care
Subject: BS5837 - shading
Hello All,
BS5837 suggests that "the current ... height of Cat A, B & C trees
should be
annotated on the TCP where this would cause unreasonable obstruction to
sun
or day light. In practise this could be represented by a segment with a
radius from the centre of the stem equal to the height from due NW to
due E
indicating shadow pattern for the main part of each day" (Section
5.3.1).
I am well aware of the limitations, pro's and cons of this but find it
to be
a useful indicator of the area most likely to be densely shaded.
I am currently involved in a site where someone has stated: "it is
generally
accepted by professional Arbs that this guidance is not entirely
accurate
and falls somewhat short of truly representing the potentially shaded
area".
So I accept that the advice in 5837 does not show every shaded area or
the
whole of the influence of a trees shade, but when assessing shade on a
more
detailed level (primarily using ArborShadow) I have found that the area
is
the most shaded (or the area most likely to be shaded - see below). It
doesn't take into account crown clearance or the varying density of each
species etc etc, but it does provide a useful indication to layout
designers
of the problematic places. I was sceptical originally but have found it
a
more than reasonable tool, after numerous detailed appraisals and
comparing
them to the 5.3.1 segment.
So here's the question: what do other think about this? Do professional
Arbs accept that this falls somewhat short? Is the shortfall with the
simplistic 5837 shade area that significant? I haven't seen much on the
forum discussing this - I'd like to hear other opinions on this.
Cheers
Dom
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