Raising the ridge height on a loft extension

[James Fyre]

If I were to put a planning application in for a loft extension to raise the ridge height of my roof by 150mm on a detached property as part of a loft extension, which is higher than other houses in the street (a row of detached and semi-detached houses that are all 8m tall) is this likely to succeed? On one hand it is against the local policy of keeping a consistent row of house heights, but on the other 150mm is not likely to be noticable on an 8m tall building.

The recent nppf changes suggest approval of all types of all upward extensions, including Mansard roofs, but the reference to a compatible height has been removed.

Here is the new text

Quote

11. Making effective use of land. §125 (e) Supporting Upward Extensions: “where the development would be consistent with the prevailing height and form of neighbouring properties and the overall street scene”.

Q1. Would local policies override the nppf?

Q2. Is the whole thing a mute point as the planning officer could argue that the "the form" of the house is too big?