Clearance from underside

[Mmtc79]

Is the 12 inches or more clearance from underside of deck boards or 12 below the bottom of deck joist ?

[Admin]

Clause 8.14.8 - A vent shall not terminate;
(h) underneath a veranda, porch, or deck unless
(i) the veranda, porch, or deck is fully open on a minimum of two sides beneath the floor; and
(ii) the distance between the top of the vent termination and the underside of the veranda, porch, or deck is greater than 1 ft (300 mm).

I would say if your vent termination is directly beneath the deck boards you need more than 12".  If you terminate directly beneath a joist then you measure more than 12" from it to the top of the vent.  It says greater than 12", so keep at least 12.1" of clearance.

[Mmtc79]

Yes I'm going to be below the deck boards and below the joist from top of vent to deck boards is about 14 inches I was just wondering if it had to be 12 inches from bottom of joist code is not very clear is just says underneath so if I went 12 below bottom of joist I'd be like 24 plus inches down lol

[Admin]

It's where the vent actually terminates.  Just keep it past any joist then you can measure from the bottom of the deck boards.