11N.I.For the purposes of paragraph 3—
(a)the erection, on land within the curtilage of any such building as is mentioned in that paragraph, of an additional building to be used in connection with the original building shall be treated as the enlargement of the original building; and
(b)where any two or more buildings comprised in the same curtilage are used as one unit for the purposes of any institution or undertaking, the reference in that paragraph to the cubic content of the original building shall be construed as a reference to the aggregate cubic content of those buildings.