Learn to install soffit with your vinyl siding installation. This video includes information on preparation, installation over open eaves, enclosed eaves and porch ceilings. Updated in 2018 to include the latest best practices.
Very good video from manufacture. Will be changing mine to a full face front panel less chance of water intrusion and easier maintenance (if needs removed).
"if the span is more than 16 inches" I never understood why they don't make 16" wide soffit panels. It is very annoying for contractors to only have a 12" option. 16" is the standard spacing, so why don't they make 16" panels?
Ok, so if you install using vinyl fascia over the fascia board you must use F-Channel attached to the facia board, but NOT if you use aluminum facia? so then you wouldnt nail your soffit to the eve, just slide it in both channel and let hang? Is that a good idea with 16" soffit width?
I did it this way with 16" vinyl soffit a year ago and it is still perfectly flat. I'm sure as you go wider you will probably need intermediate support.