Two Things I Can Think Of……

[Dodgeman]

That could possibly be the cause.

1) Is the fiberglass insulation the kraft faced type? If so, two vapor barriers have been installed. One is the foil faced Thermax, and the other is the kraft paper. This would trap moisture between them and possibly cause a moisture problem.

2) the syrofoam channels from the soffit to the ridge have to be perforated to allow the air space between the rafters to breathe and allow the moisture to vent to the ridge. If they are solid styrofoam, there is no way for the dead air space to breathe from the insulation side to the vent side.

I am assuming you have continuous soffit venting and ridge venting.

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Dodgeman