Condensation can be described as the change in moisture from a vapor to a liquid. water vapor within the house can migrate through the wall or ceiling during the heating season to some cold surface where it condenses, collecting in the form of ice or frost. During warm or sunny periods, the frost melts. When conditions are severe, this meltdown in non-vented spaces may drip to the ceiling below and damage the interior finish. Wood sheathing may swell up. Insulation becomes wet and looses it’s resistance to heat loss. These problems can be reduced or eliminated when proper construction details are used.
The control of condensation through the use of vapor barriers and ventilation should be practiced regardless of the amount of insulation used.
The use of both inlet and outlet vents in attic and roof spaces aids in keeping the air moving and preventing the accumulation of frost or condensation roof sheathing in cold areas. “Dead” air pockets in the roof can normally be prevented by good distribution of inlet vents in the soffit areas. However, there is still a need for vapor barriers; ventilation alone, when insulation is used, does not prevent condensation problems.