We have a flat roofed home and live in the Central Valley of Northern Cal. We recently dropped the celings in the bedrooms and insulated them. Is it necessary to cut vents into the outer walls for proper ventilation or is it ok as is? We have dead air space of about 3", insulation was R-38. One contractor said it was ok-another said to vent. Any suggestions?

The quaestion is, when moisture migrates into the insulation, reducing its insulating value to near zero,how will it escape?

The space above the insulation should be vented. If the insulation has a vapor retarder installed on the winter warm side of the ceiling, the net free area of the vents should be 1/300 of the area of the space above the insulation. If there is no vapor retarder, the net free area should be 1/150 of the area above the insulation.

The vents should be arranged so that there is cross-ventilation in every space between roof joists, and should be such that the openings are protected against the entrance of rain or snow.

If the space is not vented, the risk is that accumulated moisture will lead to the growth of mold and/or the occurrence of rotting of structural members.