It looks like "3 Ply Built up roof " but the rest makes no sense. Any seasoned structural engineers can tell me what this says?
I am a practicing structural engineer with plenty of wood experience. That said, this is a bit of a tricky note because I believe it was probably written by an architect on a set of architectural drawings (as opposed to by a structural engineer on a set of structural drawings). Therefore, I think the note includes information about both the structural makeup of the roof diaphragm as well as the architectural components of the roofing system. That said, I can at least get you started. I am assuming that you are in the US, but if you're in another country, the abbreviations may be a bit different. I am less sure about the second line, but am confident about the meaning of the other 4 lines.
The first line reads,
3 PLY BU ROOF
I agree that it is communicating something related to the (mostly) architectural composition of a built up roof. It likely means that the roof is a 3 ply built up roof. Depending on your intent here, if it's structural for example, this doesn't have too much importance to you.
The second line,
o/ 3/4" O.F. PLYWOOD INO.
This line is a description, of some sort, of the plywood.
o/is, I think, an abbreviation for the word "over." So the objects on this line are under the 3 ply built up roof.
3/4"is describing the plywood thickness,
OFis an old way to describe "oriented fiber" material, this is similar to oriented strand board (OSB) that you see at the hardware store today. This is a little confusing, since plywood is not oriented fiber board. It could have another meaning.
OFcould also mean "outside face" and this may be an instruction about how to apply a coating related to the built up roof to the outside face of the plywood. Also, since the plywood is given a span rating (see next point), no plywood thickness note is required so the
3/4"may not be referring to the plywood at all.
The third and fourth line,
32/16 (UNBLKD) W/ 8d @ 6" EN & RO
These lines are decribing the strucutral requirements of the plywood and associated fasteners.
32/16is a "span rating" for the plywood. From the APA,
Two numbers separated by a slash. The left-hand number is the maximum recommended center-to-center spacing for supports in inches when the panel is used for roof sheathing with long dimensions across supports. The right-hand number is the maximum center-to-center spacing of supports in inches when the panel is used for subflooring with the long dimension across supports.
(UNBLKD)is instructing that the edges of the plywood do not need to be blocked.
W/is an abbreviation for the word "with"
8d @ 6"is instructing the use of 8d nail at a spacing of 6" on center.
EN & ROis instructing that the previously mentioned nailing is applied as Edge Nailing and at Rough Openings. This means that the 6" oc nailing is applicable at the endges of the roof and around any openings.
The fifth line,
12" FNis instructing a 12" on center "field nailing." This means that the plywood should be nailed to all the rafters/joists in areas that are not diaphragm edges at a 12 oc spacing.
Good luck and please comment when you figure it out. I've passed your image around the office and it's generated quite the lively discussion!