Now that the house is complete, how can we check whether there is a lack of ventilation in the soffits and/or whether insulation has slid down and covered the soffits thereby causing a lack of ventilation there? You also indicated that there may be other causes for ice damming other than lack of ventilation in the soffits or lack of vapour barrier under the insulation in the roof cavity. What may these be and what could we possibly do about them?
Answer:
Stick your head up into the attic and if you see daylight along the lower edge, you know you have ventilation there; if you do not, you have a problem. There isn't a whole lot you can do about them in the winter but an inordinate amount of heat loss to the attic would do it as quickly as a lack of vapour barrier continuity from wall to ceiling - the two have to overlap. There are other reasons too numerous to deal with unless one is on site, but these are the main ones.
