shading study notes - cheltenham · shading study background this shading study has been prepared...
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FLAC Instruction ref. CC38‐1036
OAKHURST RISE
SHADING STUDY
Background
This shading study has been prepared in response to clarifications requested by the Cheltenham
Borough Council Tree Officer in his consultation response on the Scheme 2 planning application, CBC
ref. 18/02171/OUT.
Plots not considered likely to be subject to material tree shading effects
As part of our role as project arboriculturists for the revised scheme, we reviewed the emerging
design to ensure that proposed tree/ design relationships were acceptable, including with regard to
shading by trees of private amenity space.
Arising from this, we are able immediately to scope out the following plots:
10‐28 Located centrally within the eastern parcel & remote from trees
29‐30 Remote from trees, or few smaller trees only
34‐35 Remote from trees
44‐69 Trees generally to the north, hence no plausible shading effect
Plots potentially subject to material shading effects
We consider that the following plots are potentially subject to shading effects:
1‐5 Individual gardens
6‐9 Notional area of exterior amenity space
31‐33 Individual gardens
36‐43 Individual gardens (sampled)
We have assessed tree shading effects in relation to these plots using the proprietary software
application ArborShadow, reporting our findings below.
Notes on ArborShadow
This software takes inputs from a tree survey (in this case, that found within our planning submission
material) and uses these to model the crowns of whichever trees are considered to be of interest (in
this case, those along the southern site boundary).
Trees of interest are tested against user‐defined Points and Areas. The former can be attributed with
an elevated height, to replicate, for example, a window. Areas are used to model shading effects
within gardens (being the focus here). Tools within ArborShadow produce detailed analyses of
shading effects, in percentage terms, over the foliated months of the year.
The analyser toolkit within ArborShadow includes graphical outputs showing, for Points, binary
percentage interference graphs and, for Areas (modelled here), colour‐graded percentage
interference graphs. These latter show four levels of shading:
Green <25% Minor shading
Yellow 25‐50% Moderate shading
Blue 50‐75% Significant shading
Red >75% Severe shading
Notes on acceptability of shading
In its publication Site Layout Planning for Daylight and Sunlight – A guide to good practice (Littlefair,
BRE, 2nd edition, 2011), the Buildings Research Establishment provides the following advice:
If the whole of the garden is shaded by trees for a lengthy period of time in summer, the
garden is probably too shady (Paragraph H4.2)
BS5837:2012 states at 5.3.4(a)(2), Shading of open spaces:
Open spaces such as gardens and sitting areas should be designed to meet the normal
requirement for direct sunlight for at least a part of the day
These two authoritative sources of guidance are in agreement that unacceptable shading occurs
where there is very limited solar access within the whole of the garden and where this occurs for
most or all of the day.
Findings
Following this section we present a series of extracts from the scheme layout plan, overlaid with tree
survey data (from FLAC planning submission material), and uploaded for analysis into ArborShadow.
The plans show the Areas (gardens) which have been analysed.
Following the plan extracts are graphical outputs from the analysis tool (each labelled with
applicable plot number) within the software application, in the format already described above.
Our assessment of the ArborShadow results is set out in Table 1, below. Abbreviations used in the
Table are:
“SZA” stands for Solar Zenith Angle
“GSA” stands for Good Solar Access
It is apparent from the Table that none of the garden areas studied would receive shading beyond
the acceptability thresholds set out in BRE’s Site Layout Planning… or in BS5837:2012.
It follows that the concern over this issue expressed by the Tree Officer is shown to be misplaced.
Table 1 – Summary of ArborShadow results
Garden ref
ArborShadow shading result FLAC Assessment
1 Significant to severe shading late morning until 1700, solar access adequate either side of this subject to modest to minor interruption
Barely acceptable
2 Fair to GSA until late morning, deteriorating thereafter especially at low SZA Just acceptable
3 Fair to GSA until early afternoon, deteriorating thereafter especially at low SZA
Just acceptable
4 Minor shading until mid‐afternoon, deteriorates thereafter Acceptable
5 Good solar access for most of the day except at low SZA, and from late afternoon/ early evening
Acceptable
6‐9 Severe shading throughout the morning; GSA across the middle of the day; deteriorates thereafter. Availability of adjacent POS assists in mitigating
Just acceptable
31 Severe shading early morning; moderate to minor shading thereafter though relevant trees comprise light‐porous species so adequate solar access pm
Just acceptable
32 Minor shading across middle of the day only, though more intense at low SZA Acceptable
33 Moderate shading at high SZA until late morning; fair to GSA thereafter Acceptable
36 Minimal shading only Acceptable
37 Minimal shading, and then only at low SZA and late in the day Acceptable
38 Minimal shading only Acceptable
41 GSA throughout the day until 1800 Acceptable
43 GSA throughout the day until 1700 Acceptable
Figure 1 ‐ Site extract for plots 1‐5
ArborShadow analysis of tree shading effects, plots 1‐5
Figure 2 ‐ Site extract for plots 6‐9
ArborShadow analysis of tree shading effects, plots 6‐9 (combined)
Figure 3 ‐ Site extract for plots 31‐33
ArborShadow analysis of tree shading effects, plots 31‐33
Figure 4 ‐ Site extract for plots 36‐43 (sampled)
ArborShadow analysis of tree shading effects, plots 36‐43 (sampled)