Jim writes from northern New Zealand: "I am building in a warm humid climate. I have a sarked roof with coated aluminum tile roof, 50mm air gap, building paper, 50 mm air gap 150mm thick pink bats, 50mm air gap then gyp board(drywall). Should I put a vapor barrier on before the gyp board and what product should I use if needed."

Answer: Owens Corning recommends the use of a vapor retarder any time you are separating heated or conditioned space from non-heated or non-conditioned space. The vapor retarder is generally installed so it is directly behind the finishing material (facing the warm-in-winter side).

I should also mention that some areas with high humidity do not use a vapor retarder or turn it to the outside. Always check with your local building department for the local code in reference to vapor retarder placement.