Hi Bill
I don't mean to be picky but...
<Remember that to reduce(1) a square(2) RPA by say 30%(3) you wouldn't
reduce the sides
<of the square by 30% so the tree to building distance(4) would only go down
<slightly. Think 100m sq RPA thats 10 x 10 =100 but reduce the 10 by 30%
gives 7 x
<7 = 49, that's halved. It would be 8.5 or so. if the tree is in the middle
of
<the square it's only gone down from 5m away to 4.25 metres away.(5)
(1) I accept that Edmund talked about 'reducing' but the 2005 BS does not
mention 'reduce' in relation to RPA except following the word 'not' in
5.2.4. It deliberately uses the term 'offset' in 5.2.4 (a)
(2) If your calculated RPA is n square metres you would, unless there are
any factors to alter the rooting conditions (5.2.4 again) asume a radial
root spread. If you decide that your RPA is square, because of site factors,
then the tree is not open grown, because its root system has been influenced
by site factors, and therefore 5.2.5 (a) specifically recommends against an
offset.
(3) 30% figure is not mentioned in the BS in relation to the RPA.
(4) I would suggest that you don't describe the figure that results from an
incomplete calculation using the equation in Table 2 as a 'tree to building
distance'.
(5) The maximum offset recommended (see above about individual open grown
trees)is 20% of the radial distance because its for an open grown tree. In
your 100 metre2 example, and assuming a single stem tree, the circle would
have a radius of about 4.8m ish and 20% of that is about 1m so the offset
would be 1m, the tree centre being offset, by 1m on one compass point within
a circle with radius 4.8m and with an area of 100 metres2.
Richard 'picky' Nicholson
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