My roofer put up VentSure Heat & Moisture at the ridges and so I went around looking at the existing soffits for intake balance. Unfortunately, I don't think they did an honest NFA calculation; we have existing bird block hole soffits which if generous, are about 3" of NFA each. They installed 18" per foot NFA VentSure.
For example, in one section, about a 26 foot run, that would be around 450" NFA of VentSure and there are 37 holes (111" NFA). That's a big discrepancy. I'm sure they looked up, saw existing holes and called it done.
So two questions. First. The existing holes need to be expanded into 16x6" or 16x8" rectangle soffits to get closer to a balanced NFA. How hard is that to do when in places it can't be accessed from the inside? Cutting through the bird block and getting out the existing screening looks like a tough job (especially on tall ladders). I'm actually wondering if installing something roof-side like SmartVent might be easier.
And two. Insulation clearance. When I talked to the roofer about it the other day, when I was alarmed that a lot of the existing insulation seems to be butted up against the soffits. He said that 3/4" of clearance is all that is needed for the airflow. If there are no soffit baffles in place (which there aren't) is that reasonable?
3/4" is okay, 1" is better. Baffles should be installed to maintain that airspace.
Its not too hard to cut plywood/wood soffits from underneath, even easier if your just expanding the hole. Just use a jigsaw or sawzall and take your time, if ladder stability is a worry for you use a set of standoffs, they make a huge difference.