Whenever I tell people about straw flat roofs they don’t believe me, so here is proof What you are seeing is where a curb used to be (the OSB patch), giving a nice view of the straw insulation, we used to call it Strammit, probably a trade name.
Erik, I don’t understand this photo. I have no idea what I’m looking at. What kind of curb are you talking about? Can you please explain a little more.
Inside pic of the underside of a flat BUR roof with wood joists. Where the joists are cut and you can see the straw insulation there used to be a curb, probably for roof top HVAC duct. The curb is gone which exposed the insulation, otherwise all that was visible was the plastic vapor barrier.
I have also seen strammit (straw) insulation installed on top of the roof sheathing.