When building or work may be proceeded with.

(1) Where within a period of sixty days, or in cases falling under clause (b) of section 331 within a period of thirty days, after the receipts of any notice under section 333 or section 334 or of the further information, if any, required under section 335 the Commissioner does not refuse to sanction the building or work or upon refusal, does not communicate the refusal to the person who has given the notice, the Commissioner shall be deemed to have accorded sanction to the building or work and the person by whom the notice has been given shall be free to commence and proceed with the building or work in accordance with his intention as expressed in the notice and the documents and plans accompanying the same: