Principal elevation
The principal elevation is normally the main architectural front of the house. The government's guidance says there can be only one principal elevation, although it can comprise more than one wall. The arrangement of the house and its architectural features matter; this is not simply whichever wall the owner chooses to call the front. [1]
A house on a corner or an unusually shaped plot may need a more careful assessment than a house in a uniform terrace. Mark the relevant elevations and nearby highways on a site plan so that the classification can be explained in context. [1]
Under the normal house-extension right, an enlargement cannot project beyond a wall forming the principal elevation. There is also a restriction on projecting beyond a side elevation which fronts a highway. These are separate tests, so identifying the principal front does not necessarily free the road-facing side from restrictions. [2][1]
Side elevation and rear elevation
A side wall is not automatically a rear wall merely because the proposed room will be used as part of a rear extension. A proposal wrapping around the house may engage both side- and rear-extension limitations. The technical guide assesses the combined enlargement rather than accepting a convenient label for each component. [1]
Similarly, a stepped original rear elevation can contain several relevant rear walls. Show the original arrangement clearly before measuring projection: an existing later extension is not necessarily part of that baseline. [1]
Highway
For this guidance, highway is not limited to a busy, adopted road. The definition can include public paths and other ways, and the Order's interpretation includes unadopted streets and private ways. A pedestrian route beside the plot should therefore not be ignored solely because cars do not normally use it. [1]
The question of whether an elevation fronts a highway is a site-specific assessment, not a fixed rule that every wall visible from a road is automatically a front elevation. Use the actual relationship shown on the plans. [1]
Eaves, roof height and principal part
Eaves height and the highest part of a roof are different measurements. The technical guidance explains how to identify the eaves using the external wall and roof surface; a parapet is not automatically the eaves line. Both measurements may need to appear on an extension drawing. [1]
“Principal part” has a separate role in the upward-extension right, Class AA. It excludes lower front, side or rear extensions, whether those extensions are original or later additions. Do not assume that every existing roof can support a permitted additional storey merely because it belongs to the same house. [3][4]
Original house, existing house and curtilage
The original house means the house as it stood on 1 July 1948, or as first built if later. Existing means immediately before the proposed work. Curtilage describes the land forming part and parcel of the house and can be smaller than the overall grounds. [1]
Put these distinctions on the survey and proposal drawings. A clear key showing original walls, later additions, elevations and boundaries makes the assessment easier to follow and exposes uncertainties before a certificate or prior-approval application is submitted.