The trusses were set on top of the poles on 8' centers. When we added 8 additional trusses they had to go in between and sit on the 2 x 12's that were doubled up. If you look at my new pictures the SkyView still lets in more light than I imagined. The builders said that if they were spanning the 24" as originally planned, that they would have been pretty flimsy. With the additional board behind them, it really firmed them up with out a lot of bracing. He said it was a cleaner install in the end this way. (Not by anyone's planning.)