
Set by the local planning authority by a legal agreement, a line beyond which the front of any new building may not forecast. In an established road or street the building line is usually that of existing buildings, but can be varied by the local authority
Found on
http://www.encyclo.co.uk/visitor-contributions.php

(on a building lot) a line within, or coinciding with, the property line, beyond which it is illegal to build.
Found on
https://www.infoplease.com/dictionary/building-line
No exact match found.