2.35 In addition to the above and to avoid obstructing light to the protected garden area outlined in D18, massing of developments should not obstruct a 43 degree line, taken from a point 1.6m above the ground level at the boundary of the protected garden area - see Fig.45.

2.36 This 43 degree guideline will not apply to buildings up to 3m in height.

2.37 The 43 degree standard should not be used to generate the building form of the development. Designs with excessive stepping forms to maximise development area will likely not be supported.

2.38 If only a small portion of the building rather than a continuous elevation obstructs the 43 degree standards, then this may be accepted. This will be determined on a case-by-case basis.

2.39 All developments will still be required to follow guidance elsewhere in this document, such as D16 on separation distances and D20 on protecting light into existing windows.

2.40 Private gardens to the north of buildings should be sufficiently deep to ensure the primary usable area of the garden receives sunlight in line with BRE Guidelines. Private gardens for houses should generally be sufficiently deep to accommodate typical garden furniture - see D23.

2.41 In large developments, the massing and arrangement of buildings should allow for sufficient light and air flow to reach courtyards and other amenity spaces. This can be achieved by creating breaks in the massing or lowering the height of buildings to the south of amenity spaces.

2.42 If the light levels of amenity spaces are in doubt, developments may be required to submit a two hour sun contour test, conducted on 21 March, showing adequate levels of light are being maintained to existing rear garden spaces.

2.43 Existing and proposed gardens should meet guidance in BRE Site Layout Planning for Daylight and Sunlight, which recommends that half the area should receive a minimum two hours of sunlight on 21 March. 21 March is used by BRE as the spring equinox offers representative conditions between summer and winter as an average for the year.

2.44 Plan, section and elevation drawings should be submitted that demonstrate how the development performs relative to the guidelines outlined in this principle.

2.45 The 25 degree guideline protects the outlook and access to light of existing windows facing new development. The massing of a new development should not obstruct a line struck at 25 degree, drawn from the centre of the lowest window serving a habitable room, as set out in point a. shown in the box adjacent.

2.46 The 45 degree guidelines shown in b. and c. adjacent protect the access to light of windows in buildings adjacent to new developments. They apply to any new massing above 3m that projects beyond the prevailing building line.

2.47 The 45 degree guidelines apply both to the layout (in plan) and the height (in elevation) of new development. A line should be struck from the centre of the lowest window to a habitable room, closest to the boundary as set out in Fig.50 and Fig.51.

2.48 This guidance is based on principles set out in the BRE Guidance, and therefore if an applicant can demonstrate that their development complies with the ambitions of this guidance in another way this may be acceptable.

2.49 For all major projects, and especially the development of tall buildings, a formal daylight and sunlight assessment should be provided in accordance with the BRE Site Layout Planning for Daylight and Sunlight publication to demonstrate the proposal meets the standards.
For smaller developments, applicants will be expected to demonstrate compliance with these guidelines, however where this cannot be evidenced, applicants should provide a daylight and sunlight assessment.

2.50 A new development that does not meet the 25 degree and 45 degree guidelines may still be acceptable if it follows prevailing building lines and all other aspects of the principles D16 - D19 are met.

2.51 Some sites, particularly street-facing sites, may not be able to follow the 25 degree and 45 degree rules whilst also maintaining prevailing building lines. Where this is the case, a design that carefully follows the adjacent building lines, whilst protecting the amenity of neighbours and providing acceptable living conditions for future occupants, and which deviates from these standards, may be acceptable.

2.52 Optimisation of some specific sites may be limited by the 45 degree guideline. Exceptions where the existing urban grain suggests a rigid 45 degree may not be appropriate will be viewed on a case-by-case basis.