at the end of the winter season to prevent water vapor migration into the insulation layers during the high humidity summer season the significance of enclosing the insulation layer 13 and 15 15a in a vapor tight envelope to prevent water vapor migration into the insulation layers 13 and 15 5a during the high humidity summer season needs further explanation as explained infra water vapor will move from an area of high vapor pressure to an area of low vapor pressure therefore in the high humidity summer season the high water vapor concentrated in the ambient atmosphere will move into the insulation layers 13 and 15 15a if the vapor tight envelope is not provided because when the conditions for dewpoint are reached the water vapor in the insulation layers 13 and 15 15a condenses to form water once condensed the water will not migrate back into the ambient atmosphere at the same rate at which it entered because the weather remains preponderantly humid during summer of course the heat from the sun during the day will heat the water resulting in a portion of the water being converted to water vapor but a residual amount of water will remain unvaporized after each dewpoint condition thus during the high humidity summer season each time dewpoint conditions are reached a residual amount of water that migrated into insulation layers 13 and 15 15a as water vapor remains there in the liquid state this state this phenomena results in a build up of water in the liquid state within insulation layer 13 and 15 15a thereby reducing the thermal insulation efficiency thus during the summer months it.