4. Side Yard Exceptions. On an existing lot in a Residential District specifically
4. Side Yard Exceptions. On an existing lot in a Residential District specifically exempted from the lot width requirements hereof pursuant to G.L. c. 40A, s. 6, para. 4, the required side yard width for a dwelling or other main building may be reduced one foot for each ten (10) feet by which the width of said lot is less than the minimum specified for its district, such width being measured across the lot at the required setback line or through that part of the building where the lot Is narrowest, whichever distance is the greater; provided, however, that the side yard distance shall not be so reduced to less than sixty (60) per cent of the required minimum.