Still on the suject of venting ny hot water heater straight up thru' the roof : The code says there must be a 1" spacing between the vent pipe and "combustibles". As dumb as this question may sound, does that imply the wood flooring and roof that I must pass through? i.e. If I have a 3" diameter vent pipe, do I need 5" diameter holes through my ceiling and roof to attain that 1" clearance? Thanks.