From: Grant Leggett [grantleggett@boyerplanning.co.uk]
Sent: 11 October 2011 14:33
To: Sexton, Gavin
Subject: RE: Rear 15 Elsworthy Road
Dear Gavin,
I have provided below (and attached) our
responses on the matters you raised in your email of 15 September (your text in
red). Please let
me know that the information provided satisfies your concerns.
We would also be grateful for an update on
what Committee date we are likely aiming for.
There are a number
of points which need to be addressed with further information as follows:
1. Section through
all planters to demonstrate that roots may propagate beyond immediate confines.
It would be very helpful (possibly essential) to have a brief illustrative
demonstration of the ability of the front planters to support small specimen
trees (as indicated in DAS - such as Hazel, Holly, Fig etc - showing
specification of tree, root ball size etc.
I attach drawings 10014-223 and 205.
These drawings show the soil depth across the site and shows that trees behind
the front boundary would have unlimited root depth. Our arboricultural
consultant is satisfied that the types of trees we are considering will have
ample space to grow in the space provided. We are not proposing large
trees, but trees that would be a few metres tall that would just peek over the
wall (as indicated), although we anticipate a condition requiring details
later.
2. Detailed
section through basement roof demonstrating at least 500mm of soil cover as per
CPG.
Drawing 10014-P260 shows a detailed section
of the green roof above the basement. The drawing comes from a design by
ANS. ANS are satisfied that he green roof would be suitable for amenity
use.
The drawing does now show 500mm of soil cover,
but as previously discussed, the amount of soil cover is secondary to the
proposed green roof carrying out its intended function, which it would. Paragraph 2.64 of the
CPG is mostly about rainwater absorption and biodiversity. Even though we
will not have 500mm of soil depth the rainwater attenuation will be dealt with
in other ways (addressed below), and the biodiversity will also be a
significant improvement on existing.
3. Further
information about the mechanical plant (ie air source heat pumps referred to in
Appendix 5 of the Planning Statement, also items such as water pumps to drain
lightwells, whole house ventilcation unit etc). location
of noise/acoustic breakouts and intakes, acoustic implications for neighbours.
See in particular the issues raised in the attached letters of objection. This
point about plant noise nuisance has been raised by a number of objectors in
recent days. It is my viwe that this needs to be dealt with robustly.
The main concern regarding plant was to do
with noise nuisance caused by the location of a possible air source heat
pump. We have overcome this by switching to a ground-source system which
will be incorporated into the piles of the basement development. Drawing
60196251-SK-M-001 shows a schematic of the proposed GSHP system, and identifies
all mechanical plant that would be used in the building as part of the
heating/cooling and ventilation system.
All plant apart from a domestic extract fan
will be internal and can be easily designed to ensure compliance with relevant
acoustic standards. We anticipate a condition requiring details of any
plant to be submitted to ensure that any noise generated from internal plant
will not harm neighbour amenity.
4. I am not
entirely convinced by the SUDs proposals - ref objections relating to surface
water flooding from Primrose Hill etc
The sum of the
(reduced) surface water and foul water runoff would still exceed the current
contribution of the site to the sewer network. Can you advise on where the foul
water storage would be located if necessary (see second BIA para
) ? What potential is there for runoff water holding tanks on site - or
grey water recylcling?
The calculations
on surface water runoff are for 1 in 30 year events - our CPG requires 1-100
year calculations, which is suported by the Best Practice guidance which
supports PPS25 (para 5.51 - designing for exceedance) as follows: "no flooding of property should occur as a
result of a one in 100 year storm event (including an appropriate allowance for
climate change)."
The initial comparison between existing proposed development
discharges in our report was based on a 1 in 30 year event as this was
considered the most appropriate. The calculations below relate to the 1
in 100 year event; for either case we are not proposing an attenuation tank on
site. However, as the development is for a basement, in practice the foul
discharge will be pumped from a sump at the lowest level, this will inevitably
act as a holding tank, size of which can be adjusted at detail design stage to
suit Thames Water requirements.
·
The combined flow from the site for the 1 in 100 year storm
event is actually less than the existing surface water discharge alone
·
·
Runoff from the existing site = 4.475* l/s
Total combined flow for the proposed site for the 1 in 100 year
storm event = 2.2* l/s + 1.5* l/s (foul flow) = 3.7 l/
·
Consequently, it is not anticipated that any foul storage will
be required.
The potential for surface water flooding caused by water from
Primrose Hill is extremely limited. There are brick walls between each
garden separating the site from Primrose Hill, so surface water cannot flow
from garden to garden. Any ponding would be due to either the limited
permeability of the soil surface, or saturation of the topsoil, temporarily
causing ponding; either way this has been considered in our appraisal of the
groundwater flows, and will not increase the surface runoff onto our site.
Have there been
any further results from the monitoring of the piezometer (ref Appendix 2 of
original AECOM report para 2.2)?
Piezometer monitoring results were included in the submitted
report, we have not revisited site to obtain updated results.
I have heard it
reported that there was some site investigation in neighbouring rear
gardens relating to establishing the local water environment
characteristics - but I can see no mention of this in the revised BIA. Do you
have details/conclusions or can you comment?
We are not aware of any site investigations in neighbouring
properties.
Please call if any questions.
Grant Leggett
Associate Director
London
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020
7921 0027 
07791
144 750 
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