agree on the tension in a qp truss, in most uses. wasn't thinking about those interior rafters. was thinking about wind loading.

this building, which was done by new energy works (before my time there) uses a horizontal truss to take the load on all that glass. you can barely see it in there.





link to larger photo.
http://lh6.googleusercontent.com/-_YCOYQ...ide244+copy.jpg

look at second truss in, bottom chord area, you'll see steel tension rod coming back away from the window, acting as a horizontal truss.

its pretty crazy, what history does to buildings. would be interesting to uncover some story about this.