In the event that any act required by this chapter or by a resolution adopted pursuant to § 13.20.040 cannot be performed within the time provided on account of shortage of materials, wear, restraint by public authorities, strikes, labor disturbances, civil disobedience or any other circumstances beyond the control of the actor, then the time within which such act will be accomplished shall be extended for a period equivalent to the time of such limitation.
(`78 Code, § 13.20.180.)