PPS 7 (Addendum): Residential Extensions and Alterations
Annex A: Context and Design: Detailing
A18 Attention should be paid to design details such as the position, shape, proportion and style of windows, doors and other features to complement the existing property and respect the character and appearance of the area. To facilitate the integration of an extension or alteration with the existing property, new windows should be aligned to the existing fenestration and match the symmetry of the existing dwelling. The relationship between solids and voids is an essential component of any new proposal, but particularly when extending or altering an existing property where window size and height diminish on upper floors.
A19 Older residential properties in particular often have interesting arches, brick detailing and other special features or ornamentation which add character. Continuing or reflecting such ornamentation around doors, windows and at the eaves in the design approach followed can be an effective way of integrating any extension or alteration work with the existing property.