The term refers to unintended moisture that enters through the “Building Envelope”.  The building envelope consists of the exterior shell of your home that’s designed to repel the elements. Examples include: the roof, basement, windows & doors, exterior walls and the drainage plane, foundation waterproofing, exterior house wrap, ice and water shield, and roofing felt, that is behind the exterior finishes. Moisture intrusion can be obvious and easily found or very subtle and require instruments and testing to locate the source.