(a) Streets shall be generally considered eligible for paving when fifty (50) per cent of the lots facing thereon are occupied by buildings and when ample time has been allowed for settlement of subgrade, fills and trenches.
(b) Alleys shall generally be considered eligible for paving when one-third of the lots abutting such alleys have garages, necessary rear entrances or establishments requiring access, unless paving is required to correct a drainage condition. (Code 1953, § 18.38)