Does a building permit expire?

Any building permit issued shall be deemed abandoned and invalid unless the work authorized by it shall be commenced within six (6) months of the date of issuance.  The building official, upon written request, may issue extensions.  Work under such a permit, in the opinion of the building official,  must proceed in good faith continuously to completion so far as reasonably practicable under the circumstances.  For more information see 780 CMR Section 111.8 Expiration of Permit.