(1) Lot Width and Area.

(a) "R-18" Districts.

(.1) Single-family dwellings: The minimum lot width shall be 18 feet, and the minimum lot area shall be 1,620 square feet;

(.2) Duplex dwellings: The minimum lot width shall be 24 feet, and the minimum lot area shall be 2,160 square feet;

(.3) Multiple dwellings: The minimum lot width shall be 35 feet, and the minimum lot area shall be 1,050 square feet for each family contained therein;

(.4) Buildings other than dwellings: The minimum lot width shall be 42 feet, and the minimum lot area shall be 3,780 square feet;

(b) "R-19" Districts.

(.1) Single-family and duplex dwellings: The minimum lot width shall be 18 feet, and the minimum lot area shall be 1,620 square feet;

(.2) Buildings other than dwellings: The minimum lot width shall be 35 feet, and the minimum lot area shall be 3,150 square feet;

(.3) Multiple dwellings: The minimum lot width shall be 18 feet for a one, two or three story dwelling, 24 feet for a four-story dwelling and 30 feet for a dwelling of 5 stories, and the minimum lot area shall be 540 square feet for every family contained therein;

(2) Courts.

(a) Open courts not between the wings of the same building, when used, shall have a minimum width not less than the required minimum width of a side yard;

(b) The minimum width of an open court between wings of a building shall be 12 feet. The least dimension of an inner court shall be 8 feet. Minimum area for such court shall be 100 square feet. Such courts of less area than 300 square feet shall not be permitted for any building used for dwelling purposes, except when used as vent shafts;

(3) Application to Existing Dwellings. Any dwelling in these districts may be converted to contain a greater number of families under the following provisions:

(a) If said dwelling, as converted, will meet the Use, Area and Height Regulations as set forth above; or

(b) If, in lieu of meeting the Use, Area and Height Regulations as set forth above, the following provisions are complied with:

(.1) For the number of families to be increased, the majority of the floors of the dwelling must have an area of at least 700 square feet per floor and the total floor area must be a minimum of 1,600 square feet. In such a case, additional families may be added as follows:

Total Number of Families Permitted:

0.0 times the number of floors having 0-600 square feet

1.0 times the number of floors having 601-800 square feet

1.5 times the number of floors having 801-1200 square feet

2.0 times the number of floors having 1201-1500 square feet

2.5 times the number of floors having 1501-1800 square feet

3.0 times the number of floors having 1801 or more square feet

All figures to be rounded to lower whole number.

(.2) In addition, families shall not be added unless there is provided at least 800 square feet (300 square feet in "R-19") of yard space (including any area used for parking), for each family contained in the building;

(.3) In "R-19", in order to convert from a single-family dwelling to a duplex dwelling, a dwelling shall either have a rear yard with a minimum depth of 20 feet or comply with the requirements of sub-paragraph (.1) and (.2) above.

(c) Any construction or alteration made in connection with any conversion permitted in these paragraphs shall conform to the area and height regulations of these districts; provided, that when necessary, legally required fire escapes may exceed such regulations.