The second floor flat ceiling will tie into the tji at 12 feet hence the need for a vented assembly.
Tji roof rafters.
The applicability of this detail is based on the joist reaction at the support.
In a typical roof framed with dimension lumber the rafters rest on the exterior wall top plate at the lower end and bear against a ridge board at the top.
Conventional framing the first thing to understand is how a roof framed with wood i joists differs structurally from a traditional stick framed roof.
One more important detail.
The tji rafter run is 18 feet.
This detail is intended to reinforce the tji j oist end and not to transfer thrust loads at the rafter heel.
Tji joists are lightweight and come in long lengths which makes them faster and easier to install than traditional framing and saves you both time and money.
Technical bulletin tb 805 shows a detail for reinforcement of tji joists slope cut to match a rafter pitch.