(9)Joint open air space. - (a) Every such interior or exterior open air space, unless the latter is a street, shall be maintained for the benefit of such building exclusively and shall be entirely within the owner's own premises.(b)If such interior or exterior open air space is intended to be used for the benefit of more than one building belonging to the same owner, then the width of such open air space shall be the one specified for the tallest building as specified in sub-rules (5) and (6) of Rule 56 abutting on such open air space.(c)If such interior or exterior open air space is jointly owned by more than one person, then its width shall also be as specified in Rules 59 provided that every such person agrees in writing to allow his portion of such joint open air space to be used for the benefit of every building abutting on such joint open air space and provided he sends such written consent to the Authority for record. Such common open air space shall thenceforth be treated as a permanently open air space required for the purposes of these rules. No boundary wall between such joint open air space shall be erected or raised to a height of more than 2.0 metres.
