Insulation batt having integral baffle vent

A method of insulating and ventilating a space between rafters for supporting a roof, comprising:

• installing an insulation product with an insulation mat integral with a baffle having substantially vertical walls and a substantially horizontal bottom wall and having holes through the bottom wall of the baffle and having at least one open channel extending the length of the insulation mat, and a water vapor permeable membrane on a roof facing side or on an insulation facing side of the bottom wall and covering the holes through the bottom wall and covering at least a portion of the insulation mat that faces toward the baffle, by installing the insulation product in a space between adjacent rafters for supporting a roof of a building, with the channel facing toward an under surface of the roof for passage of ventilating air along the space between the adjacent rafters, and with the permeable membrane allowing for the transmission of water vapor emanating from the insulation mat and into the channel, wherein a vapor permeability of the vapor permeable membrane increases with increased relative humidity in the insulation;
• and
• ventilating moisture through the holes through the bottom wall of the baffle and into the ventilating air, while covering the holes through the bottom wall with the vapor permeable membrane and repelling liquid water from wetting the insulation mat, and while transmitting water vapor that emanates from the insulation mat.