Rear yard: 45 feet; provided, however, that a covered patio, deck or porch which, when attached to the rear line of the existing dwelling, would encroach into the rear yard area, and if the patio, deck or porch has a width of not more than 16 feet, then such encroachment shall be permitted, provided that there remains an open rear yard of at least 35 feet. The covered patio which encroaches into the rear yard area may not be enclosed in any manner, with the exception of screening, and may at no time be used for or become a habitable room. It is further provided that an uncovered patio, deck or porch which, when attached to the rear line of the existing dwelling, would encroach into the rear yard area, such patio, deck or porch having a width no greater than the width of the existing dwelling, shall be permitted, provided that there remains an open rear yard of at least 35 feet and the width of the patio, deck or porch does not exceed the width of the residence.