Roof Design Thoughts

I've been contemplating the roof design for my cob house. I really like the roof design of Hilde Dawe's house (pictured here). This roof has a series of roof beams visible beneath the eaves, and in the photo below, which shows the ceiling planks resting on top of these beams.

The eaves are apparently 8-10" thick. I'm assuming that there is a ventilated insulation space of 6-8" under the roof decking. What I'm wondering is just what supports the roof decking? Is there a second set of roof beams hidden inside the insulation space, upon which the roof decking rests?

I like the look of the exposed beams and planking in the loft, and you'd normally look at this design and assume that it is the roof decking you're looking at. But that's clearly not the case here. I wonder if there is some other structure in the insulation space supporting the top roof decking, or if it is in fact another set of beams. Hmm...