Your contractor would know more about local conditions and successful work practices for your area, than I possibly can. That doesn't guarantee his competence, of course. But he's in a far better position to know the 'right answer'. Assuming you did due diligence on checking him out, the prudent thing would be to (1) trust him, but (2) carefully read the terms of his guarantee, to make sure he's got skin in the game if things go wrong . . . which them sometimes do even with honest competent contractors.

Good luck!