The proposed two storey side extension will not be set back from the front elevation of the host dwelling, nor will it be set down from the principle roof ridge. Paragraph 3.38 of the Design SPD states: "Extensions should be designed so that the main property is still the dominant building. The roof and eave lines should be lower than the existing house. Setting back the extension behind the front wall of the existing house can often help to achieve a satisfactory design." The proposed extension would lead to the main building losing its dominance and would therefore unacceptably alter the built form of the dwelling. The proposed extension, by virtue of its height and mass would not be a subservient addition to the dwelling, to the detriment of its character and appearance. Policy CS2 of the Core Strategy and the supporting Design SPD places particular emphasis on side extensions such as this being subservient additions which retain their host dwelling's original form and appearance from the street scene. The proposed development would instead enlarge the bulk and scale of the building which would unbalance the visual relationship with the adjoining semi-detached property to the detriment of the street scene. It is therefore considered that the proposed two storey extension, by virtue of its form, mass and overall appearance would fail to respect the character of the existing dwelling and would result in an obtrusive feature within the street scene to the detriment of the character and appearance of the area. The proposal is therefore contrary to policies CS2 of the Core Strategy, EV1 and H/17 of the Local Plan, the Design SPD and the National Planning Policy Framework.