I just realized that my initial post is present in two different forum categories. I apologize for the duplicate post. I'm sure it's my fault. Since this version has the most activity, it seems to make the most sense for me to reply here. Thanks again for all that responded. Again, your comments were super helpful. A few additional thoughts...
I am having a little problem picturing just what you are doing.
Ha. That makes two of us. As I said, I've never done this before, nor am I following any plans. I'm just kind of doing what seems to make sense at each step. The only advice I was given (by a contractor) was to build the units separately, and then combine them. That proved to be pretty helpful... except for the fact that my floor is not level. So, some of the shelves were level when I build them on the other side of the room, but then I had to disassemble and reassemble when I slid them in place and they were sloped. Oh what fun. Luckily I figured that out early on. Anyhow...
Maybe a quick sketch would help
I can't provide a sketch... but I've attached some updated photos. I've made a bit of progress since the last photos. FYI... I hung the tv before I started on the shelves. It was a gamble (I came close to dropping wood or tools on it about a dozen times), but it was the only way I knew to guarantee perfect centering. It also provided me with something the do while I built :o)
Whether or not I used support strips across the back depended upon the length of the shelves
The middle section has ridiculous span, so I did use support strips for that. I also have inserts to break up the span. For aesthetic reasons, I also decided to put the support spans on the top side
of the shelf, and screw them in (deck screws) from the bottom. I don't know how useful this will prove to be (working against gravity... I know)... but hopefully it'll prolong the sagging process by some years.
Unless you are doing something that I cannot picture, you have no need of glue.
Hopefully that's still the case after the pictures. With that said, there is one area that I think I'm going to use glue for after all. As I inch towards this part of the project, I realize that I'm a little nervous about hanging a 1x10x8 across the top to cover the void on the top and bottom. The bottom one (part of it is leaning in place in the picture) will obviously be supported by the floor. But the weight of the top one worries me. At this point I'm thinking screws and glue
will help me sleep better at night. The vertical edges (where the side boards come together for each unit) will be trimmed also, so the top horizontal plank will also be sitting on that (I hope I'm describing this in a way that makes sense) so that should help also. When it's all said and done (caulked, painted, etc.) the top and bottom will also have crown molding and base boards across it to match the rest of the room. Oh... and the space between the last unit on the right and the wall is intentional. This is on an external wall, so it has horizontal studs. I'm hoping to use the channel on the right (which will be covered) to run wires to the attic space as needed. So, finally... a question: Is hanging 1x10 (pine) planks across the top a bad idea? If so, any other suggestions?
Phew... that was a lot (sorry).
Thanks again for your expertise and insight.