Great question — answering as the UphillTech team:
The style of finish with several narrow vertical boards placed on broader surfaces is called board and batten . The battens are used to hides seams of the broader sections, and in more primitive construction, to fill cracks, block air, and improve insulation. The battens are not meant to be structural, but when nailed, screwed, or glued into place, add some minor additional rigidity to the structure. The horizontal and angled strips are also primarily decorative, but fill roles similar to the battens.
Full answer by bib: https://diy.stackexchange.com/a/86668 (CC BY-SA 3.0).
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