One problem or question that I run into on a weekly basis is regarding the question of creating a double vapour barrier on the exterior wall of a new home. Many building codes require a vapour barrier on the warm side of the wall(inside), usually behind your drywall.
However, many builders are now installing rigid foam on the exterior of the walls beneath the siding as extra insulation to boost the R-Value and energy efficiency of the house. The problem is that all rigid foam products are relatively impermeable to moisture and can cause a sandwiching effect, or double-vapour barrier effect on your walls. Moisture in the walls cannot properly escape, and will run down to your bottom plates, causing rot, mildew, and related problems.
The option that I offer to customers and builders who insist on using rigid foam on the outside of the building is to use a "Smart Vapour Barrier" instead of the usual polyethylene vapour barrier sheets. This will allow moisture to gradually escape the walls instead of being trapped and causing problems. This is especially helpful in climates with extreme weather fluctuations(hot summer to snowy winters.) See the MemBrain site here for more info.
However, many builders are now installing rigid foam on the exterior of the walls beneath the siding as extra insulation to boost the R-Value and energy efficiency of the house. The problem is that all rigid foam products are relatively impermeable to moisture and can cause a sandwiching effect, or double-vapour barrier effect on your walls. Moisture in the walls cannot properly escape, and will run down to your bottom plates, causing rot, mildew, and related problems.
The option that I offer to customers and builders who insist on using rigid foam on the outside of the building is to use a "Smart Vapour Barrier" instead of the usual polyethylene vapour barrier sheets. This will allow moisture to gradually escape the walls instead of being trapped and causing problems. This is especially helpful in climates with extreme weather fluctuations(hot summer to snowy winters.) See the MemBrain site here for more info.
