Sven, move to the head of thre class! The wall was an outside wall; last summer this space was covered (but not truly "enclosed"), and the new roof blocked view of the strobe.
The "precision notched purlin" is, in fact, a modified I-beam.
As for 'critters.' well, I arrived on day #2 of the job to find a squirrell eating the heart of my print! Don't you hate it when that happens?