I am building an addition in Nebraska and need some advice on insulation and ventilation in the attic. I have closed cell foam in the walls (5 inches) and am scheduled for R38 batt (11.5 inches) with R19 batt (5.5 inches) on top of the R38, both over a 6 mil plastic vapor barrier. This is above a bathroom and closet on the hot (south) side of the house.

I have stapled styrofoam baffles 8 ft long in every rafter opening (14) to the underside of the roof that should help air flow from the eave vents to the ridge vent. The top of the openings on the baffles are more than 36 inches above the attic joists (attic floor). Roof slope is 5/12 and the distance from attic floor to ridge is 5 feet at the peak.

My concerns are:

1) Is a certain "volume" of air required in the attic to prevent condensation?

2) Is there something I am missing?

3) Can too much insulation cause havoc and how?

Thanks in advance for any advice.