Cool vid.
I am curious, why would they would staple the bottom of the shingle when that would just be an entry point for water (making the shingles less useful)?
Let me begin with, I have no experience in Japanese roofing. I do have many decades in residential and commercial construction. Much of this time in building envelope design and application (roofing & waterproofing one subcategory of building envelope). Little experience with hand split wood shingles.
I would assume those staples are stainless.
The EXTREEME thinness of those wood shingles would make them very susceptible to lifting in wind at the exploded edge (if the edge is not secured).
The shingles appear to be installed in a triple coverage method (three layers of shingle minimum coverage), with no asphaltic felt or other underpayment being used (somewhat typical to increase breathability of the wood (reduced rot potential).
I do agree, the use of thru-fasteners appears questionable, and would think some method of adhesive application would be superior ...
The sheer thinness coupled with the exposed fasteners had me wondering if this application is possibly for a facade ... (appearance vs. weather exposure protection), sometimes known as "doll house shingles".
Then again, like I say my Japanese architectural experience is limited to what I have done/learned here in the U.S. Could be the superior quality of the wood, and related performance is just off the chart for me.
As a reference point; wood shakes around me are split (much thicker than shingles). Wood shingles are typically sawn (to get them thin and even).
Hand split shingles I think are 1/4" - 5/8" thick. In the video it seemed they were consistently producing =<1/4" nominal (finished thickness 1/4" or less).
I was actually more impressed with the quality of those wood bolts than anything else. Craftsmen pretty good too. The knives/froes ... meh
I would love to learn the true scoop on the actual application.
Regards,