(a) Every permit shall remain valid for purposes of this part if the work on the site authorized by that permit is commenced within 12 months after its issuance, unless the permittee has abandoned the work authorized by the permit.
(b) A permittee may request an extension of a permit. The building official may grant, in writing, one or more extensions of time for periods of not more than 180 days per extension. The permittee shall request an extension pursuant to this subdivision in writing and demonstrate justifiable cause for the extension.