Section 2(103) in Assam Notified Urban Areas (Other than Guwahati) Building Rules, 2014
(103)"rear air plane" means the plane contained between the ground behind the building and the straight line drawn downwards and outwards from the line of intersection of the outer surface of any rear wall of the building with the roof perpendicular to that line and at an angle 63 1/2 degree to the horizontal;
