Taped Zip System sheathing — applied continuously on the walls, over the plumb-cut rafter ends, and up the slope of the roof — provides the primary air barrier.
Note the layer of housewrap under the eaves, installed in advance as the rafter tails were being added. Later, the entire shell was covered with housewrap.
To avoid the gaps in the air barrier that typically occur where the rafters cross the top plates, the author decided to apply false rafter tails to the outside of the airtight shell, first installing a course of a self-adhering flashing membrane to seal fastener penetrations.
Unused attic spaces are part of the home's conditioned space, so the rafters are insulated up to the ridge. Note that plywood is used in the attic to hold the insulation in place where there is no drywall.