I contacted a roofing supply company and have found some great 4 inch R 30 insulation for the outside of the roof. It has a thin layer of "fibre board" on either side. They recommend that the vapour barrier should go next to the roof. I was hoping to glue the insulation to the roof to maximize the effect. Do you know how to create a vapour barrier so that it can be glued to? The process is be: sheeting, vapour barrier, 4 inch insulation, 2X2 for ventilation, new sheeting, shingles. Or is there another way of going about it?
Answer:
You've got it right but the only way you'll be sure to have a continuous vapour barrier is to use ice and water shield with at least a six-inch overlap and glue your insulation's fibre board to it. Ice and water shield closes around nail shafts to retain its impermeability.
