I am building an addition to a home in northern Idaho.  The existing home has fiberglass batt insulation and I would like to use blown-in dense pack cellulose in the addition.  There will be cathedral ceilings and I’ve heard dense packing with no venting is an option.  The addition and the existing house sit corner to corner with a slight overlap.  Both have gable roofs with perpendicular ridges thus a short valley in between.   My main question is whether I will create a strange situation for snow in the valley where one semi-warm roof and one semi-cold roof meet?  Will this adversely affect the snow sliding off the metal roof?  Any other comments on blown- in cellulose would be appreciated too.