Buying a new bungalow in New Brunswick, Canada, and this is a second problem that the inspector I hired found that the inside attic roof was all frosted over, and he said that it's not normal. He checked the insulation and venting, and it looked fine. He concluded that since attic hatch had no insulation, the heat and humidity coming up the attick trap door were caking the roof with frost, and would make the wood rot. The contractor, on the other hand, says that frost on the inside attic roof is normal, and won't have any adverse effects. A friend at work suggested that since it's a new house, and the summer was especially damp and humid, that the whole house is sweating the excess humidity, and it is all collecting on the roof.
He said that it should eventually fade away.
Since it can get really cold up here, I wasn't too concerned about the frost, but if it can rot my roof...

Should I insulate the attic hatch? The inspector wants at least 6" of hard insulation.

Note: I have an air exchanger to circulate the air in the house.

Any help would be appreciated.